WO2006119786A1

WO2006119786A1 - Method for stabilization of dc-potential at the output of a preamplifier and amplifier circuit

Info

Publication number: WO2006119786A1
Application number: PCT/EP2005/004986
Authority: WO
Inventors: Jan Kaplon
Original assignee: European Organisation For Nuclear Research - Cern
Priority date: 2005-05-09
Filing date: 2005-05-09
Publication date: 2006-11-16

Abstract

The invention relates to a method for stabilization of a direct current potential at at least one output of a first preamplifier circuit, wherein the first preamplifier circuit comprises at least one amplification element (13) and at least one active feedback circuit (23, 29) with at least one active feedback resistor element comprising at least one first electrode connected at least indirectly to an input (17) of the amplification element (13) and at least one second electrode connected at least indirectly to an output (19) of the amplification element (23) wherein the conductance of the active feedback resistor element (23) between the first and the second electrode is adjustable, and wherein an operating and/or a bias point of the active feedback resistor element (23) is set so that the active feedback resistor element (23) is operated in a saturation region.

Description

EUROPEAN ORGANISATION FOR NUCLEAR RESEARCH

CERN

1211 Geneva 23 Switzerland

Method for stabilization of DC-potential at the output of a preamplifier and amplifier circuit

Description

The present invention refers to a method for stabilization of a direct current potential at at least one output of a first preamplifier circuit, wherein the first preamplifier circuit comprises at least one amplification element and at least one active feedback circuit with at least one active feedback resistor element comprising at least one first electrode connected at least indirectly to an input of the amplification element and at least one second electrode connected at least indirectly to an output of the amplification element wherein the conductance of the active feedback resistor element between the first and the second electrode is adjustable, an amplifier circuit, comprising at least one first preamplifier circuit especially usable in the method according to the invention, and an evaluation circuit.

hi different commercial, industrial, medical and scientific instrumentation applications it is necessary that signals from a sensor have to be amplified before a further processing of the signals is possible. For example detectors used for particle position sensing comprise a plurality of sensors producing signals in form of small current charge signals that has to be converted in voltage pulses that are then shaped, amplified and analysed. The pulse height of this voltage pulses is mainly proportional to the energy deposited in the detector by each photon or particle striking the detector. For the conversion of such small current charge signals charge sensitive amplifiers comprising at least one preamplifier followed by at least one main amplifier or gain stage circuit are used. Usually the different channels of the detector signals are amplified and analysed in respective amplifier circuits.

As can be understood from the description above, an amplification with high gain is necessary to achieve the wanted conversion of the small current charge signals into the voltage pulses for the further analysis. To achieve such a high gain it is important that the direct current (DC) potential at the input of a main amplifier circuit following a preamplifier circuit is within a pre-described range, hi the state of the art it is common to use so-called active feedback preamplifiers (AFP) for each signal channel of the detector that are connected in series to at least one main amplifier or gain stage circuit, respectively.

For example the US 6,587,003 B2 discloses a charge sensitive preamplifier with a pulsed source reset. This charge sensitive preamplifier for a radiation detector includes an amplifier having a JFET input (stage) and a capacitive feedback element, wherein the amplifier produces an output voltage proportional to a charge pulse deposited at the JFET input by the radiation detector, hi the US 6,587,003 B2 it is proposed to use a circuitry connected to the amplifier output and to a source node of a JFET to provide to the source node a pulsed reset signal to achieve a reset of the capacitive feedback element. The disadvantage of this system is that by each reset signal an unwanted pulse is produced at the output of the preamplifier.

Furthermore in the article "GaAs-Based High-Gain Direct-Coupled Distributed Preamplifier Using Active Feedback Topology", IEEE Microwave and Wireless components letters, Vol. 14, January 2004, it is proposed to reach an amplification by a cascade of at least two distributed amplifiers with a DC-blocking capacitor. Connected to the input of the second distributed amplifier is a DC-Level-Shift Circuit that allows a bias tuning for the second amplifier to set a predefined bias and/or operating point of the following amplification stage.

Finally the US 5,793,254 discloses a generic amplifier circuit comprising an active feedback preamplifier wherein a feedback circuit is connected in parallel to an amplification element. The feedback circuit comprises a feedback capacitor to which an active feedback transistor is connected in parallel. The active feedback transistor is operated in the linear region and the gate of the transistor is connected to a bias circuit to produce a constant voltage. To achieve a stable resistance of the feedback transistor and to reduce the influence of production spreads of the feedback transistor it is proposed that in the bias circuit a replica of the feedback transistor is used. To allow the coupling of the preamplifier stage to a following amplification stage it is proposed that at the output of the preamplifier stage a pole-zero-circuit comprising an AC-coupling element in form a capacitor is used. By such an AC-coupling element the propagation of DC-variations from the active feedback preamplifier output to the next amplifier stage is avoided but this leads to the disadvantage that an undershoot on the signal response is present which is caused by the differentiation of the signal by the coupling capacitor and the input impedance of the following amplification stage.

It is therefore the object of the present invention to provide a method for the stabilization of a direct current potential of a preamplifier circuit overcoming the drawbacks of the prior art.

Furthermore it is an object of the present invention to provide an amplifier circuit and an evaluation circuit also overcoming the drawbacks of the prior art.

The object concerning the method is achieved in that an operating and/or a bias point of the active feedback resistor element is set so that the active feedback resistor element is operated in a saturation region, whereby a potential difference between at least one third electrode of the active feedback resistor element and the second electrode is adjusted mainly irrespective of the potential difference between the first and the second electrode via a current flowing through the active feedback resistor element, and that the direct current potential at the output of the first preamplifier circuit is adjusted by applying a control voltage to the third electrode.

With the invention it is especially proposed that at least one parameter of the active feedback resistor element, especially the operating and/or the bias point, is controlled by adjusting the current flowing through the active feedback resistor element, especially through the first electrode.

In the two above described embodiments it is furthermore preferred that at least one parameter of the active feedback circuit, especially further comprising at least one capacitor, being preferably connected in parallel to the amplification element and/or the active feedback resistor element, as at least one noise parameter and/or at least one time constant, is or are controlled by adjusting the current flowing through the active feedback resistor element, especially flowing through the first electrode.

The inventive method can also be characterized in that the control voltage is generated based on a comparison of a predefined set voltage value, preferably generated in at least one set voltage generator, and at least one actual potential value.

For this embodiment it is proposed with the invention that the predefined set voltage value mainly corresponds to a set value of a bias voltage of at least one main amplifier circuit connected to the output of the first preamplifier circuit.

One special embodiment of the invention is characterized in that as the actual potential value at least one actual potential value at the output of the first preamplifier circuit is used, whereby preferably the direct current potential at the output of the first preamplifier circuit is regulated in a closed loop.

In an alternative embodiment of the invention it is preferred that as the actual potential value at least one actual potential value at at least one output of at least one second preamplifier circuit, being preferably mainly a replica of the first preamplifier circuit is used.

Furthermore it is proposed that the control voltage is filtered before being applied to the third electrode.

Finally the inventive method can be characterized in that a signal of at least one signal source, preferably a small current charge signal generated by at least one sensor, especially comprised in at least one detector used for particle position sensing, is applied to the input of the first preamplifier circuit.

The object concerning the amplifier circuit is achieved by an amplifier circuit comprising at least one first preamplifier circuit, especially usable in the method according to the invention, wherein the first preamplifier circuit comprises at least one amplification element, at least one active feedback circuit with at least one active feedback resistor element comprising at least one first electrode connected at least indirectly to an input of the amplification element and at least one second electrode connected at least indirectly to an output of the amplification element, wherein the conductance of the active feedback resistor element between the first and the second electrode is adjustable, and wherein an operating and/or a bias point of the active feedback resistor element is adjustable so that the active feedback resistor element is operated in a saturation region, whereby a potential difference between at least one third electrode of the active feedback resistor element and the second electrode is adjustable mainly irrespective of the potential difference between the first and the second electrode via a current flowing through the active feedback resistor element, and that the direct current potential at an output of the first preamplifier circuit is adjustable by applying a control voltage to the third electrode.

For the amplifier circuit it is proposed that the active feedback circuit further comprises at least one capacitor, preferably being connected in parallel to the amplification element and/or the active feedback resistor element.

Further with the invention it is proposed that the first preamplifier circuit comprises at least one first current source, preferably connected to the input of the amplification element, for generating at least one, preferably adjustable, first current flowing through at least the active feedback resistor element, especially through the first electrode.

According to the invention the amplifier circuit can be characterized in that by means of the first current at least one parameter of the active feedback circuit, preferably of the active feedback resistor element, especially the operating and/or the bias point of the active feedback resistor element, and/or at least one noise parameter and/or at least one time constant of the active feedback circuit is or are controllable.

Also it is proposed that the amplification element comprises at least one amplifier, preferably at least one operational amplifier.

A preferred embodiment of the invention can be characterized in that the amplifier comprises at least two amplification transistors connected in cascode configuration, wherein preferably at least one buffer transistor is connected to one of the amplification transistors in source follower configuration.

Furthermore with the invention it is proposed that the active feedback resistor element comprises at least one single-element device, preferably at least one transistor, and/or at least one multi-element device, preferably at least one amplifier, especially one operational amplifier.

This embodiment can be further characterized in that the at least one transistor is a bipolar transistor, wherein preferably the collector electrode of the bipolar transistor works as the first electrode of the active feedback resistor element, the emitter electrode of the bipolar transistor works as the second electrode of the active feedback resistor element and/or the base electrode of the bipolar transistor works as the third electrode of the active feedback resistor element.

In an alternative embodiment of the invention it is proposed that the at least one transistor is a field-effect transistor, preferably a junction field-effect transistor (JFET) or a metal- oxide-semiconductor field-effect transistor (MOSFET), particularly a depletion MOSFET or Enhancement MOSFET, wherein especially the drain electrode of the field-effect transistor works as the first electrode of the active feedback resistor element, the source electrode of the field-effect transistor works as the second electrode of the active feedback resistor element and/or the gate electrode and/or the bulk electrode of the field-effect transistor works as the third electrode of the active feedback resistor element. With the invention it is also proposed that at least one control circuit at least indirectly connected to the third electrode.

With the invention it is suggested in this embodiment that the control circuit comprises at least one comparator circuit, preferably in form of an error amplifier and/or a differential amplifier, with at least one output connected at least indirectly to the third electrode of the active feedback resistor element, at least one first input connected at least indirectly to at least one set voltage generator, and at least one second input, wherein to the second input preferably an actual potential can be applied.

Said amplifier circuit can also be characterized in that the second input of the comparator circuit, preferably the error amplifier, is at least indirectly connected to the output of the first preamplifier circuit.

hi an alternative embodiment it is proposed that the second input of the comparator circuit, preferably the differential amplifier, is at least indirectly connected to the output of at least one second preamplifier circuit.

For this alternative embodiment it is preferred that the second preamplifier circuit is mainly a replica of the first preamplifier circuit.

A further embodiment of the invention can be characterized in that the first preamplifier circuit is connected to at least one signal source, preferably generating small current charge signals, like at least one sensor especially comprised by at least one detector used for particle position sensing.

The two embodiments mentioned above can be characterized in that to the input of the second preamplifier circuit no signal is applied, preferably that the input of the second preamplifier circuit is not connected to the signal source.

It is also proposed with the invention that the third electrode of the active feedback resistor element of the second preamplifier circuit is tied to a fixed reference potential. In this embodiment it is preferred that the circuit amplifier according to claim 26, characterized in that the fixed reference potential is ground.

In an alternative embodiment it is suggested that the amplifier circuit according to claim 26, characterized in that the active feedback resistor element is a n-channel metal-oxide semiconductor (NMOS) transistor and/or the fixed reference potential is a positive supply voltage.

One special embodiment of the invention can be characterized in that the output of the first preamplifier circuit is connected at least indirectly to at least one main amplifier circuit.

For this embodiment it is proposed with the invention that the main amplifier circuit comprises at least two amplification transistors connected in cascade configuration, wherein the amplification transistors are preferably connected via a closed feedback loop circuit.

Finally the amplifier circuit according to the invention can be characterized in that the set voltage generator comprises at least one replica of a single element of the main amplifier circuit, preferably at least of one of the amplification transistors of the main amplifier circuit, preferably to regenerate the current flowing in the closed feedback loop circuit of the of the main amplifier circuit.

The object concerning the evaluation circuit is achieved by an evaluation circuit wherein the evaluation circuit comprises a plurality of amplifier circuits according to the invention.

With the invention it is proposed that the evaluation circuit is connected to at least one detector, preferably used for particle position sensing and/or comprising a plurality of sensors, especially for sensing different signal channels of the detector, connected to the amplifier circuits respectively.

A special embodiment of the invention can be characterized in that at least two first preamplifier circuits, preferably the active feedback resistor elements of at least two preamplifier circuits, are connected to one common control circuit. Finally it is proposed with the invention that the common control circuit comprises at least one second preamplifier circuit, especially being a replica of at least one of the first preamplifier circuits.

It is, therefore, the astonishing perception of the present invention that by a suitable adjustment of the operation and/or bias point of an active feedback resistor element within an active feedback circuit of an active feedback preamplifier circuit beside the advantages that a high value feedback resistance for a low noise performance of the preamplifier can be achieved as well as that it is possible to adapt the time constant of the active feedback circuit to achieve a high quality preamplification, the quality of the whole amplifier circuit comprising the active feedback preamplifier connected in series with at least one main amplifier circuit can be significantly highered in this way that the DC-potential at the output of the preamplifier can be stabilized by an appropriate control of the active feedback resistor element within the active feedback circuit.

To reach this aim the operating point of the active feedback resistor element, especially in form of a transistor, is chosen in this way that the active feedback element is working in a saturation region. This means that in case that for example a field-effect-transistor (FET) is used as an active feedback resistor element and that the source electrode of the FET is connected to the output of the preamplifier circuit, that the gate to source voltage of the FET is in the first order defined by the current flowing through the transistor. This effect can be used to stabilize the direct current potential at the output of the preamplifier in the following way.

The active feedback resistor element is connected to the amplification element of a preamplifier in this way that the first electrode of the element (drain electrode of the FET) is connected to the input of the amplification element whereas a second electrode of the element (source electrode of the FET) is connected to the output of the amplification element. Furthermore the active feedback circuit comprises preferably a capacitor connected in parallel to the first electrode and the second electrode of the active feedback resistor element. The preamplifier circuit does furthermore comprise a first current source by means of which the current flowing through the active feedback resistor element can be adjusted. The current flowing in the active feedback resistor element defines its transconductance between the first and second electrode and the parameters of the active feedback circuit. Furthermore by the current of the first current source the noise performance and the timing performance, this means at least the time constant of the filter configuration comprising the capacitor and the active feedback resistor element in the active feedback circuit, is set.

As mentioned above when the active feedback resistor element is operated in its saturation region by changing the current flowing through the active feedback resistor element the potential difference between a third electrode (gate electrode of the FET) and the second electrode is changed. As the third electrode of the active feedback resistor element is connected to the output of the amplification element, representing the output of the preamplifier circuit, when the current flowing in the active feedback resistor element is in the range of hundreds of nA to few μA, the variation of the DC-potential at the output of the active feedback preamplifier might be up to few hundreds of mV.

This can create the problem for the following main amplifier stage circuit applied to the output of the active feedback preamplifier when it is working in transimpedance configuration that the operation point of this amplifier stage circuit has to be readjusted to obtain the required signal amplification level of the whole amplifier circuit.

The method and the amplifier circuit according to the invention is based on the surprising finding that when the active feedback resistor element is run in the saturation region the DC-potential at the output of the preamplifier circuit can be directly adjusted by applying a control voltage to the third electrode of the active feedback resistor element (gate electrode of the FET). This will change the potential at the third electrode and as the voltage between the third and second electrode (gain and source electrode of the FET) is defined in the first order by the current flowing through the active feedback resistor element as this is in the saturation region, the potential at the second or source electrode will follow these changes leading to the result that the DC-potential at the output of the preamplifier circuit is also changed. In this way it is not necessary to take further actions to avoid the propagation of a DC variation at the output of the active feedback preamplifier circuit to the next amplifier circuit like introducing an AC-coupling between the active feedback preamplifier circuit and the main amplifier circuit, for example in form of a capacitor. Especially the disadvantage of this AC-coupling, that the signal that has to be amplified is distorted for example by an undershoot of the signal, caused by the differentiation of the signal by the coupling capacitor and the input impedance of the following amplifier circuit, is avoided.

To achieve the wanted stabilization of the DC-potential at the output of the active feedback preamplifier circuit with the invention different ways how an adequate control voltage can be applied to the active feedback resistor element, especially the gate electrode of an FET, are provided. The control voltage can be generated for example in the following ways:

The DC-potential at the output of the preamplifier circuit can be regulated, especially by a closed loop, in this way that the active feedback resistor element, especially the gate electrode of an FET, is connected to the output of an error amplifier. By means of the error amplifier the control voltage is obtained as a difference of the actual DC-potential at the output of the preamplifier circuit and a reference voltage obtained from a set voltage generator also called bias voltage generator. In case a change of the DC-potential at the output of the preamplifier circuit occurs in this way that this DC-potential differs from the set value predefined by the set voltage generator, a change of the control voltage applied to the active feedback resistor element will occur. As the active feedback resistor element is run in a saturation region the DC-potential at the output of the preamplifier circuit follows directly the change of the control voltage.

Furthermore with the invention the following way of generating a control voltage applied to the active feedback resistor element is provided. By using the following control method instead of a (closed-loop) regulation as described before, where each active feedback preamplifier circuit has to be provided with the above described regulation circuit, the power consumption and the occupied silicon area for the whole evaluation circuit comprising a plurality of active feedback preamplifier circuits for the plurality of signal channels that has to be amplified separately, can be reduced. As mentioned above an evaluation circuit of a small current charge detector usually comprises a plurality of preamplifier circuits wherein for each channel of the signal one preamplifier circuit is used. In the following these active feedback preamplifier circuits are also called first preamplifier circuits or regulated active feedback preamplifier circuits. All these regulated active feedback preamplifier circuits are connected to respective sensors of a detector the signal of which has to be analysed. The whole evaluation circuit furthermore comprises a second active feedback preamplifier circuit also called reference preamplifier circuit, being mainly a replica of a regulated active feedback preamplifier circuit with the difference that the input of the reference preamplifier circuit is not connected to the sensors and that to the active feedback resistor element of this reference or second preamplifier circuit a fixed reference voltage is applied, whereas to the active feedback resistor element of the regulated preamplifier circuits the variable control voltage is applied.

Replica in the sense of this application means that at least the overall configuration and connections of the first and second preamplifier circuit are the same. It is preferred that mainly identical single devices are used in the first preamplifier circuit and in the replica as this leads to an easier implementation of the whole evaluation circuit during a CMOS fabrication process. By using mainly identical single elements especially the sensitivity of the circuit to significant tolerance variations between manufacturing runs can be minimized.

For the stabilization of the DC-potential at the output of the regulated preamplifier circuits a control voltage which is equal to the difference between the DC output of the reference preamplifier circuit and the set DC-potential generated by a set voltage generator is applied to the active feedback resistor element of each regulated preamplifier circuit, preferably after a filtering.

To reach this aim it is for example proposed with the invention that the set voltage generator is connected to one input of an operational amplifier working in a differential configuration whereas the second input of the operational amplifier is connected to the output of the reference preamplifier circuit. The output of this operational amplifier is connected to the active feedback resistor elements of the regulated preamplifier circuits of the different channels to reach a stabilization of the DC-potential at the output of these regulated preamplifier circuits. By using a replica of a regulated preamplifier circuit that is not connected to a sensor of the detector the plurality of preamplifier circuits for each channel, which are mainly identical to each other, can be controlled in this way that the control voltage is not affected by the detector signals. Thus by the evaluation circuit provided by the invention and using the claimed method a full control and stabilization of the output DC voltage of preamplifier circuits is enabled which allows the simple DC connection between preamplifier circuits and following main amplifier circuits, as high gain shaper stages, especially avoiding the necessity of an AC-coupling between the preamplifier and the shaper stage. Furthermore as the control voltage is generated in a separate control circuit, when a replica of the regulated preamplifier circuit is used to generate an actual value of the DC-potential at the output of the preamplifier circuit, which has no connection to the detector and is thus not affected by detector signals, the regulated preamplifier circuits can copy with high rates of the detector signals in comparison to a separate regulation for each preamplifier circuit for each channel as high and variable signal rates could cause low frequency oscillations at the preamplifier circuit output when this output is used to regulate the control voltage applied to the active feedback resistor element. Especially no further steps have to be taken to achieve a high quality filtering of the control voltage in high counting applications as the control voltage is not influenced by the sensor signal. Furthermore by the use of one reference preamplifier circuit only one circuit for generating the control voltage per evaluation circuit can be used that can serve several channels of the evaluation circuit leading to a minimization of power consumption and occupied silicon area.

Thus an application specific integrated circuit (ASIC) is provided that comprises charge sensitive preamplifiers with active feedback circuits. This front end ASIC can especially be used for semiconductor trackers (SCT), solid-state detectors, counting and similar applications.

The invention, together with further objects and advantages, may best be understood with reference to the following description taken in conjunction with the accompanying drawings, in which Fig. 1 is a simplified schematic representation of an amplifier circuit according to a first embodiment of the invention;

Fig. 2 is a schematic representation of an amplifier circuit according to a second embodiment of the invention;

Fig. 3 is a schematic representation of a part of a chip implementing the amplifier circuit according to Fig. 2;

Fig. 4a is a diagram showing the DC potential at the output of a reference preamplifier circuit for different currents flowing in the active feedback circuit;

Fig. 4b is a diagram showing different control voltages applied to the active feedback resistor element of a regulated preamplifier circuit; and

Fig. 4c is a diagram showing the DC-potential at the output of a regulated preamplifier circuit according to the invention.

In Fig. 1 an amplifier circuit 1 is shown. The amplifier circuit 1 comprises a preamplifier circuit 3 and a main amplifier circuit 5. An input 7 of the preamplifier circuit 3 is connected to a sensor 9. This sensor 9 is especially comprised by a detector used for particle position sensing and produces signals in form of small current charge signals. By means of a preamplifier circuit 3 these small current signals are converted into voltage pulses that are then shaped and can be then further amplified and analyzed. It has to be understood that a detector for particle position sensing comprises a plurality of sensors 9. Each sensor 9 senses a separate channel of the detector and is connected to its own amplifier circuit. Thus, the amplifier circuit 1 of Fig. 1 is used to amplify the signals of one channel of the detector comprising the sensor 9. Thus, as it becomes apparent from Fig. 1, in the amplifier circuit 1 the main amplifier stage 5 is directly connected to an output node 11 of the preamplifier circuit 3. To reach a high quality amplification it is necessary that the DC-potential at the node 11 is mainly constant as it defines the operation point of the main amplifier circuit 5. In case the operation point of the main amplifier circuit 5 is not within a predefined range, it might be saturated.

In the first embodiment of the invention in form of the amplifier circuit 1 a stabilization of the DC-potential at the output node 11 is reached in the following way:

The preamplifier circuit 3 comprises an amplification element in form of an operational amplifier 13. An active feedback circuit 15 is connected in parallel to an input 17 and an output 19 of the operational amplifier 13. The active feedback circuit 15 comprises mainly a feedback capacitor 21 connected on one side to the input 17 and on the other side to the input 19 and an active feedback resistor element in form of an active feedback transistor 23. The active feedback transistor 23 is realized in form of a field effect transistor (FET) of the PMOS type. The drain electrode of the active feedback transistor 23 is connected to the input 17 whereas the source electrode of the active feedback transistor 23 is connected to the output 19 of the operational amplifier 13. The preamplifier circuit 3 further comprises a current source 25. This current source generates a current I_feedback which flows through the active feedback circuit 15, especially the active feedback transistor 23. By setting the current I_feedback flowing in the active feedback transistor 23 the transconductance of the active feedback transistor 23 is defined as well as other parameters of the active feedback circuit 15 like the time constant.

To reach the stabilization of the direct current potential at the output node 11 of the preamplifier circuit 3 the active feedback transistor 23 is operated in its saturation region. This leads to the following behavior of the active feedback transistor 23. Through the first (drain) electrode of the active feedback transistor 23 the current I_fee_dbac_k is flowing. As the active feedback transistor 23 is operated in the saturation region the potential difference between the third (gate) electrode and the second (source) electrode of the active feedback transistor 23 is in the first order defined by the current Ifeed_back flowing through the drain electrode of the active feedback transistor 23. Thus, by applying a control voltage to the gate electrode of the transistor 23, what will change the gate potential, because of the predefined potential difference between the gate and source electrode, the potential at the source electrode will follow this change. As the source electrode of the transistor 23 is directly connected to the output node 11 of the preamplifier circuit 3, by applying the control voltage at the gate of the transistor 23 the DC-potential at the output node 11 can be controlled and adjusted.

By an appropriate control by a control circuit connected to the gate electrode of the transistor 23 the DC-potential at the output node 11 can be stabilized. In the embodiment shown in Fig. 1 this aim is reached by a control circuit comprising a comparator circuit in form of an error amplifier 29 and a set voltage generator in form of a bias voltage generator 31. The output of the error amplifier is connected to the gate electrode of the transistor 23. One input of the error amplifier 29 is connected to the bias voltage generator 31. A second input of the error amplifier 29 is connected to the output node 11 of the preamplifier circuit 3. In this way the control voltage applied to the gate electrode of the transistor 23 is obtained as a difference of the DC-potential of the regulated channel at the output node 11 of the preamplifier circuit 3 and a set voltage obtained from the bias voltage generator 31. In case the actual potential value at the output node 11 differs from the set value generated by the bias voltage generator 31 the control voltage applied to the gate electrode of the transistor 23 is changed. As the potential difference between the gate and the source electrode of the transistor 23 is mainly defined by the current feed_back the change of the gate potential leads directly to a change of the source potential of the transistor 23 thus changing the DC-potential at the output node 11.

Although the embodiment of the invention shown in Fig. 1 leads to a very good stabilization of the DC-potential at the output node 11 of the preamplifier circuit 3 in high counting applications this regulation method might have problems related to the efficiency of filtering of the signal pulses in the control circuit comprising the error amplifier 29. Furthermore, high and variable signal rates can cause low frequency oscillations at the output node 11 of the preamplifier circuit 3.

These effects can be avoided for example by using an amplifier circuit according to the second embodiment of the invention shown in Fig. 2. According to Fig. 2 an amplifier circuit 51 according to the second embodiment of the invention comprises similar to the amplifier circuit 1 shown in Fig. 1 a first preamplifier circuit 53 and a main amplifier circuit 55. An input node 57 of the preamplifier circuit 53 is connected to a sensor 59 whereas an output node 61 of the preamplifier circuit 53 is connected to the main amplifier circuit 55. Also the preamplifier circuit 53 comprises an amplification element in form of an amplifier 63 that can be realized in form of an operational amplifier connected to an active feedback circuit 65. The active feedback circuit 65 is connected to an input 67 and to an output 69 of the amplifier 63 and comprises a feedback capacitor 71 as well as an active feedback transistor 73 in form of a PMOS transistor. Also the preamplifier circuit 53 comprises a current source 75 for providing a current I_feedback flowing through the active feedback transistor 73. The operating point of the amplifier 63 is set by a biasing circuit (not shown), hi contrast to the embodiment shown in Fig. 1 the DC-potential at the output node 61 of the preamplifier circuit 53 is not regulated in a closed loop but controlled by a control voltage which is applied in the following way to the gate electrode of the transistor 73.

As shown in Fig. 2 the gate electrode of the transistor 73 is connected to a control circuit comprising a comparator circuit in form of a differential amplifier circuit 79, a set voltage generator, in form of a bias voltage generator 85 and a second preamplifier circuit 53'. The differential amplifier circuit 79 comprises an operational amplifier 81 and respective resistor elements 83a, 83b, 83c, 83d. Although the gate electrode of the transistor 73 is directly connected to the differential amplifier circuit 79 this connection can be realized also including the integration of at least one filter element which is not shown in Fig. 2. A first input of the differential amplifier circuit 79 is connected to the bias voltage generator 85. The core idea of the amplifier circuit 51 shown in Fig. 2 is that the second input of the differential amplifier circuit 79 is connected to the second preamplifier circuit 53'. As can be seen from a comparison of the first preamplifier circuit 53 and the second preamplifier 53' the second preamplifier circuit 53' is a replica of the preamplifier circuit 53. This means that the overall configuration and the connections within the second preamplifier circuit 53' are the same as in the first preamplifier circuit 53. Furthermore, the single elements used in the second preamplifier circuit 53', namely the amplifier 63', the feedback capacitor 71' and the active feedback transistor 73' as well as the current source 75', are replicas of the corresponding single elements of the first preamplifier circuit 53. It is also possible that the feedback capacitor 71' has a capacitance being larger than the one of the feedback capacitor to provide a filtering of the regulation voltage as the feedback capacitor 71' does not influence the DC output of the second preamplifier circuit 53'. The difference between the first preamplifier circuit 53 and the second preamplifier circuit 53' is that the second preamplifier circuit 53' is not connected to a sensor of a detector and that the gate electrode of the active feedback transistor 73' is tied to a constant potential V_reference applied via node 77'. The second preamplifier circuit 53' is also called reference (active feedback) preamplifier circuit whereas the preamplifier circuit 53 is also called regulated (active feedback) preamplifier circuit.

In the following the method used to reach a stabilization of the DC-potential at the output node 61 of the regulated preamplifier circuit 53 is described. The feedback transistor 73 is operated in the saturation region and thus the potential at the source electrode of the feedback transistor 73 can be directly influenced by the control voltage applied to the gate electrode of the transistor 73, in turn directly influencing the DC-potential at the output 61. The control voltage applied to the gate electrode of the transistor 73 is equal to the difference between the DC output of the separated reference preamplifier circuit 53' and a required DC-potential defined by the output of the bias voltage generator 85. Preferably the potential at the output of the bias voltage generator 85 is equal to the required DC-potential at the output node 61. When the current I_feedba_ck generated by the current source 75 is changed to adjust the transconductance of the feedback transistor 73 and/or other parameters of the active feedback circuit 65, especially to optimize the noise and timing performance of the preamplifier circuit 53, the potential difference between the gate electrode and the source electrode of the feedback transistor 73 is changed thus leading to a change of the DC-potential at the output 61. As the second or reference preamplifier circuit 53' is a replica of the first or regulated preamplifier circuit 53 also the potential difference between the gate and source electrode of the feedback transistor 73' is changed when the current Ifeedbac_k generated by the current source 75' being equal to current Ifeedback generated by current source 75 is changed. As the feedback transistor 73' is a replica of the feedback transistor 73 also the transistor 73' is operated in the saturation region. A change of the potential difference between the gate electrode and the source electrode of the transistor 73' leads to a change of the direct current potential at the output of the reference preamplifier circuit 53' as the reference voltage applied to the node 77' is fixed. As the set voltage generated by the bias voltage generator 85 is constant this change of the direct current potential output of the second preamplifier circuit leads to the result that the control voltage applied to the gate of the feedback transistor 73 is changed. More precisely when the current I_feedbac_k is increased in both of the first and second preamplifier circuit 53, 53' the potential difference at the gate and the source electrodes of the feedback transistors 73, 73' increases which results in the DC-potential at the output node of the second preamplifier circuit 53' being increased. The usage of the differential amplifier circuit 79 leads to the result that following to this increase of the output potential of the reference preamplifier circuit 53' the control voltage applied to the gate of the transistor 73 in the regulated preamplifier circuit 53 is decreased, keeping a constant value of the potential on node 61 or in other words in this way the DC-potential at the output node 61 of the first preamplifier circuit 53 is fixed at the level of the set voltage generated by the bias voltage generator 85.

The main advantage of the embodiment of the invention shown in Fig, 2 is that a control of the DC-potential at the output of the first preamplifier circuit 53 is not influenced by any signals generated by the sensor 59. Thus, low frequency oscillations at the output of the preamplifier circuit 53 are avoided.

A further advantage of this control method using a reference preamplifier circuit being a replica of a regulated preamplifier circuit is that one common control circuit comprising a bias generator and a reference preamplifier circuit connected respectively to a differential amplifier circuit can be used for a plurality of preamplifier circuits used for different channels of a detector. Usually on one integrated circuit, which is used for the analysis of a plurality of channels of a detector, a plurality of replicas of a preamplifier circuit is existing for the plurality of channels. One of these replicas of the preamplifier circuit already existing on the integrated circuit can be used as the reference preamplifier circuit used in the control circuit shown in the Fig. 2. The only change that has to be made is that the reference preamplifier circuit is not connected to a sensor of the detector and that to the active feedback resistor element of the preamplifier circuit, especially an active feedback transistor operated in the saturation region, a constant voltage is applied.

In Fig. 3 a simplified schematic of a part of an integrated circuit, especially realized in IBM 0.25 μm CMOS technology, of the circuit shown in the Fig. 2 is pictured. For simplification reasons the same reference numbers are used in Fig. 3 as in Fig. 2.

Firstly the configuration of the first preamplifier circuit 53 and of the second preamplifier circuit 53' is described. The preamplifier circuits 53, 53' are connected via nodes 87, 87' with a non-shown power supply. In Fig. 3 the configuration of the amplifiers 63 and 63' is shown in more detail. The preamplifier circuits 53 and 53' are based on buffered cascode configuration amplifiers with respective NMOS input transistors 89, 89' respectively connected in cascode configuration to transistors 91, 91'. A respective cascode/bias voltage is applied to the nodes 93, 93' connected to the gate electrodes of the transistors 91, 91'. Furthermore, the preamplifier circuits 53, 53' comprise respective current sources 95, 95' providing an equal bias current for the input stages of the preamplifier circuits 53, 53'. The preamplifier circuits 53, 53' furthermore comprise respective transistors 97, 97' working as buffer transistors in source-follower configuration. By the buffer transistors 97, 97' a low output impedance of the amplifiers 63, 63' is reached.

Although in Fig. 3 the use of low output impedance buffer source followers as operational amplifiers is shown, the invention is not restricted to this configuration of an operational amplifier used in the respective preamplifier circuits. Other configurations of an operational amplifier known in the state of the art can be used. In the configuration of the preamplifier circuits 53, 53' shown in Fig. 3 by using PMOS transistors as respective active feedback transistors 73, 73' it is possible that the potential at the node 77' of the transistor 73' is ground. This leads beside a higher control range for the preamplifier circuit to a further simplification of the used circuit and makes the implementation of the amplifier circuit on an integrated circuit easier.

The pulse gain of the shown preamplifier circuit 53 is in the range of 3 to 4 mV/fC. The required final gain which is usually in the range of about 20 mV/fC is obtained in the main amplifier circuit 55. This main amplifier circuit 55 consists mainly of two cascaded amplifiers working in common drain configuration. These amplifiers are realized in form of a PMOS transistor 101 and a NMOS transistor 103. The main amplifier circuit 55 comprises furthermore a buffer transistor 105 which source is connected to an output 107 of the main amplification circuit 55. The DC gain of the main amplifier circuit 55 is defined by the ratio of resistors 109 and 111 building a closed feedback loop within the main amplifier circuit 55. This closed feedback loop creates a negative feedback for the cascaded transistors 101, 103. Furthermore, the drain of the transistor 101 is connected to the power supply via a resistor 113.

As described above in the bias voltage generator 85 preferably a set value for the DC- potential at the output of the regulated preamplifier circuit 53 is generated. For this purpose the bias voltage generator 85 is connected to the power supply of the amplifier circuit via a node 87". To avoid any dependency on manufacturing tolerances of the respective devices used in the main amplifier circuit 55 and the bias voltage generator 85 some devices comprised in the bias voltage generator 85 are replicas of devices used in the main amplification circuit 55. Especially the transistors 101' and 103' are respective replicas of the transistors 101 and 103 used in the main amplifier circuit 55. Furthermore, the resistors 111' and 113' are replicas of the resistors 111 and 113 used in the main amplification circuit 55.

To achieve an adequate set value at the output of the bias voltage generator 85, directly representing the wanted current potential at the input of the main amplifier circuit 55, the bias voltage generator 85 firstly further comprises a current source 115 generating a current which is equal to the current flowing through the resistor 109 of the main amplifier current 55. Secondly, the bias voltage generator 85 comprises a current source 117 generating a current that is equal to the current flowing through the resistor 109 of the main amplifier circuit 55 plus the current generated in a current source 119 of the main amplifier circuit 55. In this way the bias voltage generator 85 generates a set value for the DC- potential at the input of the main amplifier circuit 55 using the currents that are flowing also in the main amplification circuit 55, namely the current flowing through the resistor 109 and the current generated by the current source 119, to adjust the wanted bias point of the main amplifier circuit 55. Thus, the set voltage generator 85 takes advantage of the effect that on one hand the DC-potential at the input of the main amplifier circuit 55 defines all currents in the main amplifier circuit 55, and thus on the other hand by the use of replicas of single elements used in the main amplifier circuit 55 in the bias voltage generator 85, especially of the amplification transistors 101, 103, and by generating respective currents in the bias voltage generator 85 that are equal to the currents flowing in the main amplifier circuit 55 when a respective DC-potential voltage is applied to the input of the main amplifier circuit 55, the adequate set value for the DC-potential can be "regenerated".

hi the figures 4a to 4c respective potential values existing in the amplification circuit 51 are pictured. In Fig. 4a different DC-potentials U₁ at the output of the reference preamplifier circuit 53' are shown. As can be seen from the graphs 121, 123 in Fig. 4a the DC-potential U₁ at the output of the reference preamplifier circuit 53' is 800 mV in case a current fe_edback of 2μA is flowing through the feedback transistor 73' (see graph 121) whereas the DC-potential U₁ at the output of the reference preamplifier circuit 53' is 600 mV in case a current feed_back of 0.4 μA is flowing through the feedback transistor 73' (see graph 123). Thus, a variation of 1.6 μA of feedb_ack leads to a variation of 200 mV at the output of the preamplifier circuit 53' in case the potential at the gate electrode of the feedback transistor 73' is not changed.

hi Fig. 4b the control voltages U₂ applied to the gate electrode of the feedback transistor 73 of the regulated preamplifier circuit 53 for the different currents feedback of 0.4 μA and 2 μA are shown. As can be seen from Fig. 4b a change of fee_dback from 0.4 μA, leading to a DC-potential U₁ of 600 mV at the output of the second preamplifier circuit 53', to 2μA, leading to a DC potential U₁ of 800 mV at the output of the preamplifier circuit 53', leads to a change of the control voltage U₂ from 310 mV (see graph 121') to 130 mV (see graph 123'). hi this way the variation of the DC-potential at the output 69 or node 61 of the preamplifier circuit 53 which is equal to the change of direct current potential U₁ shown in Fig. 4a as the circuit 53' is a replica of the circuit 53 and the same current feedback is flowing in both circuits, is compensated by the control voltage U₂ as can be seen from Fig. 4c. In Fig. 4c the voltage U₃ at the node 61 is shown also for the two currents fe_edback of 0.4μA and 2μA. As can be derived from Fig. 4c the variation in the current fe_edback, which leads to a variation of the DC potential U₁ at the output of the second preamplifier circuit 53' of 200 mV, leads to a variation of the DC- potential U₃ at the node 61 of less than 8 mV. Thus, as the DC-potential at the output of the preamplifier circuit is stabilized so that it is mainly constant, the bias point of the following main amplifier circuits is not influenced, leading to the wanted high quality amplification with a high gain.

Although modifications and changes may be suggested by those skilled in the art, it is the intention of the applicant to embody within the patent warranted hereon all changes and modifications as reasonably and probably come within the scope of its contribution to the art. Especially the features disclosed in the foregoing description, in the claims and/or in the accompanying drawings may, both separately and in any combination thereof, be material for realizing the invention in diverse forms thereof.

Reference List

I amplifier circuit

3 preamplifier circuit

5 main amplifier circuit

7 input

9 sensor

I 1 output node

13 operational amplifier

15 active feedback circuit

17 input

19 output 1 feedback capacitor 3 active feedback transistor 5 current source 7 node 9 error amplifier 1 bias voltage generator

1 amplifier circuit 3, 53' preamplifier circuit 5 main amplifier circuit 7 input 9 sensor 1 output node 3, 63' amplifier 5 active feedback circuit 7 input 9 output 1, 71' feedback capacitor 3, 73 ' active feedback transistor 75, 75' current source

77 node

79 differential amplifier circuit

81 operational amplifier

83a, 83b, 83c, 83d resistor element

85 bias voltage generator

87, 87', 87" node

89, 89' transistor

91, 91' transistor

93, 93' node

95, 95' current source

97, 97' buffer transistor

101, 101' transistor

103, 103' transistor

105 transistor

107 output

109, 111, 111\113, 113' resistor

115, 117, 119 current source

121, 123, 121', 123' graph

Claims

1. A method for stabilization of a direct current potential at at least one output of a first preamplifier circuit, wherein the first preamplifier circuit comprises at least one amplification element and at least one active feedback circuit with at least one active feedback resistor element comprising at least one first electrode connected at least indirectly to an input of the amplification element and at least one second electrode connected at least indirectly to an output of the amplification element wherein the conductance of the active feedback resistor element between the first and the second electrode is adjustable, characterized in that an operating and/or a bias point of the active feedback resistor element is set so that the active feedback resistor element is operated in a saturation region, whereby a potential difference between at least one third electrode of the active feedback resistor element and the second electrode is adjusted mainly irrespective of the potential difference between the first and the second electrode via a current flowing through the active feedback resistor element, and that the direct current potential at the output of the first preamplifier circuit is adjusted by applying a control voltage to the third electrode.

2. The method according to claim 1, characterized in that at least one parameter of the active feedback resistor element, especially the operating and/or the bias point, is controlled by adjusting the current flowing through the active feedback resistor element, especially through the first electrode.

3. The method according to claim 1 or 2, characterized in that at least one parameter of the active feedback circuit, especially further comprising at least one capacitor, being preferably connected in parallel to the amplification element and/or the active feedback resistor element, as at least one noise parameter and/or at least one time constant, is or are controlled by adjusting the current flowing through the active feedback resistor element, especially flowing through the first electrode.

4. The method according to one of the preceding claims, characterized in that the control voltage is generated based on a comparison of a predefined set voltage value, preferably generated in at least one set voltage generator, and at least one actual potential value.

5. The method according to claim 4, characterized in that the predefined set voltage value mainly corresponds to a set value of a bias voltage of at least one main amplifier circuit connected to the output of the first preamplifier circuit.

6. The method according to claim 4 or 5, characterized in that as the actual potential value at least one actual potential value at the output of the first preamplifier circuit is used, whereby preferably the direct current potential at the output of the first preamplifier circuit is regulated in a closed loop.

7. The method according to claim 4 or 5, characterized in that as the actual potential value at least one actual potential value at at least one output of at least one second preamplifier circuit, being preferably mainly a replica of the first preamplifier circuit is used.

8. The method according to one of the preceding claims, characterized in that the control voltage is filtered before being applied to the third electrode.

9. The method according to one of the preceding claims, characterized in that a signal of at least one signal source, preferably a small current charge signal generated by at least one sensor, especially comprised in at least one detector used for particle position sensing, is applied to the input of the first preamplifier circuit.

10. An amplifier circuit (1, 51), comprising at least one first preamplifier circuit (3, 53), especially usable in the method according to one of the preceding claims, wherein the first preamplifier circuit (3, 53) comprises at least one amplification element (13, 63), at least one active feedback circuit (15, 65) with at least one active feedback resistor (23, 73) element comprising at least one first electrode connected at least indirectly to an input (17, 67) of the amplification element (13, 63) and at least one second electrode connected at least indirectly to an output (19, 69) of the amplification element (13, 63), wherein the conductance of the active feedback resistor element (23, 73) between the first and the second electrode is adjustable, characterized in that an operating and/or a bias point of the active feedback resistor element (23, 73) is adjustable so that the active feedback resistor element (23, 73) is operated in a saturation region, whereby a potential difference between at least one third electrode of the active feedback resistor element (23,73) and the second electrode is adjustable mainly irrespective of the potential difference between the first and the second electrode via a current flowing through the active feedback resistor element (23, 73), and that the direct current potential at an output (11, 61) of the first preamplifier circuit (3, 53) is adjustable by applying a control voltage to the third electrode.

11. The amplifier circuit according to claim 10, characterized in that the active feedback circuit (15, 65) further comprises at least one capacitor (21, 71), preferably being connected in parallel to the amplification element (13, 63) and/or the active feedback resistor element (23, 73).

12. The amplifier circuit according to claim 10 or 11, characterized in that the first preamplifier circuit (3, 53) comprises at least one first current source (25, 75), preferably connected to the input (17, 67) of the amplification element (13, 63), for generating at least one, preferably adjustable, first current flowing through at least the active feedback resistor element (23, 73), especially through the first electrode.

13. The amplifier circuit according to one of the claims 10 to 12, characterized in that by means of the first current at least one parameter of the active feedback circuit (15, 65), preferably of the active feedback resistor element (23, 73), especially the operating and/or the bias point of the active feedback resistor element (23, 73), and/or at least one noise parameter and/or at least one time constant of the active feedback circuit (15) is or are controllable.

14. The amplifier circuit according to one of the claims 10 to 13, characterized in that the amplification element comprises at least one amplifier, preferably at least one operational amplifier (13, 63).

15. The amplifier circuit according to claim 14, characterized in that the amplifier (63) comprises at least two amplification transistors (89, 91) connected in cascode configuration, wherein preferably at least one buffer transistor (97) is connected to one of the amplification transistors (89, 91) in source follower configuration.

16. The amplifier circuit according to one of the claims 10 to 15, characterized in that the active feedback resistor element comprises at least one single-element device, preferably at least one transistor (23, 73), and/or at least one multi-element device, preferably at least one amplifier, especially one operational amplifier.

17. The amplifier circuit according to claim 16, characterized in that the at least one transistor is a bipolar transistor, wherein preferably the collector electrode of the bipolar transistor works as the first electrode of the active feedback resistor element, the emitter electrode of the bipolar transistor works as the second electrode of the active feedback resistor element and/or the base electrode of the bipolar transistor works as the third electrode of the active feedback resistor element.

18. The amplifier circuit according to claim 16, characterized in that the at least one transistor is a field-effect transistor (23, 73), preferably a junction field-effect transistor (JFET) or a metal-oxide-semiconductor field-effect transistor (MOSFET), particularly a depletion MOSFET or Enhancement MOSFET, wherein especially the drain electrode of the field-effect transistor (23, 73) works as the first electrode of the active feedback resistor element, the source electrode of the field- effect transistor (23, 73) works as the second electrode of the active feedback resistor element and/or the gate electrode and/or the bulk electrode of the field- effect transistor (23, 73) works as the third electrode of the active feedback resistor element.

19. The amplifier circuit according to one of the claims 10 to 18, characterized by at least one control circuit (29, 31, 79, 53', 85) at least indirectly connected to the third electrode.

20. The amplifier circuit according to claim 19, characterized in that the control circuit comprises at least one comparator circuit, preferably in form of an error amplifier (29) and/or a differential amplifier (79), with at least one output connected at least indirectly to the third electrode of the active feedback resistor element (23, 73), at least one first input connected at least indirectly to at least one set voltage generator (31, 85), and at least one second input, wherein to the second input preferably an actual potential can be applied.

21. The amplifier circuit according to claim 20, characterized in that the second input of the comparator circuit, preferably the error amplifier (29), is at least indirectly connected to the output (19) of the first preamplifier circuit (3).

22. The amplifier circuit according to claim 20, characterized in that the second input of the comparator circuit, preferably the differential amplifier (79), is at least indirectly connected to the output of at least one second preamplifier circuit (53').

23. The amplifier circuit according to claim 22, characterized in that the second preamplifier circuit (53') is mainly a replica of the first preamplifier circuit (53).

24. The amplifier circuit according to one of the claims 10 to 23, characterized in that the first preamplifier circuit (3, 53) is connected to at least one signal source, preferably generating small current charge signals, like at least one sensor (9, 59) especially comprised by at least one detector used for particle position sensing.

25. The amplifier circuit according to claim 23 or 24, characterized in that to the input of the second preamplifier circuit (53') no signal is applied, preferably that the input of the second preamplifier circuit (53') is not connected to the signal source (59).

26. The amplifier circuit according to one of the claims 23 to 25, characterized in that the third electrode of the active feedback resistor element (73') of the second preamplifier circuit (53') is tied to a fixed reference potential.

27. The amplifier circuit according to claim 26, characterized in that the fixed reference potential is ground.

28. The amplifier according to claim 26, characterized in that the active feedback resistor element is a n-channel metal-oxide semiconductor (NMOS) transistor and/or the fixed reference potential is a positive supply voltage.

29. The amplifier circuit according to one of the claims 10 to 28, characterized in that the output of the first preamplifier circuit (11, 61) is connected at least indirectly to at least one main amplifier circuit (5, 55).

30. The amplifier circuit according to claim 29, characterized in that the main amplifier circuit (55) comprises at least two amplification transistors (101, 103) connected in cascade configuration, wherein the amplification transistors (101, 103) are preferably connected via a closed feedback loop circuit (109).

31. The amplifier circuit according to claim 29 or 30, characterized in that the set voltage generator (85) comprises at least one replica (101', 103') of a single element of the main amplifier circuit (55), preferably at least of one of the amplification transistors (101, 103) of the main amplifier circuit (55), preferably to regenerate the current flowing in the closed feedback loop circuit (109) of the of the main amplifier circuit (55).

32. An evaluation circuit, characterized in that the evaluation circuit comprises a plurality of amplifier circuits according to one of the claims 10 to 31.

33. The evaluation circuit according to claim 32, characterized in that the evaluation circuit is connected to at least one detector, preferably used for particle position sensing and/or comprising a plurality of sensors, especially for sensing different signal channels of the detector, connected to the amplifier circuits respectively.

34. The evaluation circuit according to claim 32 or 33, characterized in that at least two first preamplifier circuits, preferably the active feedback resistor elements of at least two preamplifier circuits, are connected to one common control circuit, preferably comprising one common second preamplifier circuit.

35. The evaluation circuit according to claim 34, characterized in that the common control circuit comprises at least one second preamplifier circuit, especially being a replica of at least one of the first preamplifier circuits.