CN1021496C

CN1021496C - Automatic control circuit for frequency-variable receiver

Info

Publication number: CN1021496C
Application number: CN 90106195
Authority: CN
Inventors: 侯绍义
Original assignee: Individual
Current assignee: Individual
Priority date: 1990-12-14
Filing date: 1990-12-14
Publication date: 1993-06-30
Anticipated expiration: 2005-12-14
Also published as: CN1062310A

Abstract

An AGC circuit is arranged in non-linear circuits of a frequency mixer, a rectifier, etc. of a frequency-changing receiver; the automatic gain control of a complete machine is realized through the gain of the non-linear circuits is controlled; thereby, the harmful effect on a high-level linear circuit, an intermediate-level linear circuit, etc. from the AGC control process is reduced; thereby, the performance and the production of the reliever are good.

Description

Automatic control circuit for frequency-variable receiver

The present invention relates to be used for a kind of AGC system on the Conversion Receiver.

In the receiver of existing frequency conversion receiving unit and automatic gain control thereof, the AGC controlled circuit all be arranged in the linear circuit (height put level and in put a grade circuit), this bring influence can for the work of circuit itself.

Above-mentioned this mode has the circuit of AGC owing to be subjected to the influence of AGC control signal, can not remain on the optimum Working separately; High Amplifier Circuit can bring noise when gain controlled variation, thereby influences the variation of machine-noise ratio.The AGC control that centering is put can increase the nonlinear distortion of this grade, when the one pass gain excursion is big, even makes channel plot that strange the change be taken place, and reduces the performance of receiver.Therefore the AGC dynamic range of single-level circuit can only design in a small range, will realize that for the requirement of complete machine AGC dynamic range this makes troubles for design and production by multistage controlled circuit is set.

The objective of the invention is to adopt the AGC controlled circuit is set in the nonlinear circuit of receiver, reduce the influence of AGC, provide performance and productivity better receiver linear circuit.

The present invention realizes by in the transistor mixer (frequency transformation stage) of receiver and wave detector AGC being set:

Control mixing gain makes the intermediate-freuqncy signal size of frequency mixer output change with the AGC control signal, and the AGC frequency mixer is finished the frequency translation and the gain controlling of passage as the mixing system that is subjected to AGC control.In the frequency mixer, transistor is operated in the inelastic region, adds the negative feedback network that is subjected to the AGC signal controlling in circuit, makes the nonlinear state of service area, changes with the negative feedback size; Dark non-linear the reducing of negative feedback, the mixing gain descends, and negative feedback weakens non-linear recovery, the roller rising that gains frequently.Because mixting circuit itself is to be operated in nonlinear state to finish frequency translation, be subjected to can not produce the nonlinear distortion of signal again and channel is very become after the AGC signal controlling.Receiver of the present invention is the received signal detection with intermediate frequency output, part rectified signal produces the AGC control signal by the AGC voltage forming circuit, the AGC control signal is fed back in the frequency mixer, by the negative feedback network in the frequency mixer, mixer gain is controlled, it is increased with received signal reduce, received signal weakens and increases.Thereby make the output of complete machine constant.The AGC dynamic range 40-80db of AGC frequency mixer.

The same with the AGC frequency mixer, in triode detector, be provided with and be subjected to the negative feedback of AGC signal controlling to change the non-linear working state of detection triode, thereby the detection gain is changed, finish to received signal separate the mediation gain controlling, become the AGC wave detector.The present invention is in the Conversion Receiver of the bigger AGC dynamic range of needs, AGC wave detector and AGC frequency mixer is provided with simultaneously, to enlarge the AGC dynamic range.

Fig. 1 is first embodiment of the present invention, the AGC control signal that produces the detection of intermediate frequency output signal, through the AGC voltage forming circuit also feeds back in the AGC frequency mixer, gain to it is controlled, thereby makes the constant AGC mixing receiver circuit block diagram of detection output.

Fig. 2 is second embodiment of the present invention, and the AGC signal is controlled the receiver circuit block diagram of frequency mixer and wave detector simultaneously.

Fig. 3 is the AGC mixer schematic diagram based on first embodiment of the invention.

Fig. 4 is made of the AGC mixer schematic diagram of high-gain, wide AGC dynamic range two field effect transistor.

Fig. 5 is for being subjected to the AGC detector circuit schematic diagram of AGC signal controlling based on the detection gain of second embodiment of the invention.

With reference to accompanying drawing, first embodiment of the present invention is described: among Fig. 1, the input signal that is received by antenna is put 1 voltage that amplifies back and local oscillator 2 through height and is added to together that mixing produces intermediate-freuqncy signal in the AGC frequency mixer 3, exports late-class circuit to after intermediate frequency amplification 4 and detection 5.Wherein, a part of inspection skin output signal feeds back to AGC mixing system 6, the gain of AGC frequency mixer is controlled.Above-mentioned AGC mixing system 6 is made up of AGC frequency mixer, AGC voltage forming circuit 7; Output signal after a part of detection obtains the AGC control signal behind the AGC voltage forming circuit, the size of AGC mixer gain changes with the power of this control signal, thereby makes detection output constant.

Fig. 3 is the AGC mixer of Fig. 1, and the impedance magnitude of the emitter degeneration network 9 of mixing triode 8 has determined the gain of frequency mixer.Above-mentioned negative feedback network 9 is made up of resistance 10, diode 11, shunt capacitance 12.Resistance 13 is biasing resistors of network, and triode 14 is control valves of network.AGC control signal voltage is added in the base stage of control valve 14.During in control signal voltage＜0.4 volt, control valve 14 is cut and is ended, and power supply produces 4-6mA bias current electric currents by resistance 13, diode 11, resistance 10, this moment diode positively biased, dynamic electric resistor is very little, the interchange negative feedback minimum of network 9, the mixing gain is maximum.When received signal strengthens detection output is increased, thereby when AGC control signal voltage is increased; Behind AGC control voltage＞0.4 volt, control valve 14 begins conducting gradually, its collector current is ascending to be increased with AGC control voltage increases, and the generation shunting reduces the electric current on the diode 11 gradually in circuit, the dynamic electric resistor that diode presents increases thereupon gradually, the interchange negative feedback of network is increased gradually, and mixer tube 8 nonlinear states reduce gradually, and the mixing gain descends gradually.Instead cut partially when ending when the electric current on the diode 11 is decreased to, the interchange negative feedback of network reaches the darkest, and the non-linear of mixer tube 8 reduces to minimum, and this moment, the mixing gain dropped to minimum.AGC dynamic range＞the 50db of this circuit.

The AGC mixer of Fig. 4 for constituting by two field effect transistor, AGC dynamic range＞80db.Resistance 15, variable capacitance diode 16, shunt capacitance 17 and resistance 18, variable capacitance diode 19, constitute the voltage-controlled negative feedback network 22 of source electrode of dual gate FET 20 and field effect transistor 21 respectively, resistance 23 is the biasing resistor of network, and triode 24 is the control valve of network.Change the magnitude of voltage of the bleeder circuit that control valve 24 and biasing resistor 23 form by AGC control signal voltage, make to be added in variable capacitance diode 16,19 both end voltage and to change, the variable capacitance diode capacity changes, thereby changes negative feedback depth.Reach the purpose that changes the mixing gain.Intermediate-freuqncy signal after the mixing after frequency-selecting transformer 25 is selected intermediate frequency, deliver to intermediate frequency amplifier.

Fig. 5 is the AGC detector circuit based on second embodiment of the invention.Triode 26 is operated in the detection operating state, it is respectively the biasing resistor and the oxide-semiconductor control transistors of network that resistance 27, diode 28, electric capacity 29 are formed emitter-base bandgap grading negative feedback network 30, resistance 31 and triode 32, the emitter degeneration size that changes triode 26 as mentioned above can change the non-linear working state of this pipe, thereby reaches the purpose that changes the detection gain.The low frequency signal of triode 26 collector electrodes output is delivered to late-class circuit and is amplified after the further filtering CF signal of filter of 35 groups of

electric capacity

33,34 and inductance.

Claims

1, the present invention relates to the automatic gain control circuit of Conversion Receiver, putting level, frequency transformation stage, intermediate frequency amplifier, demodulator, AGC control system by height forms, it is characterized in that: the AGC control system is to be based upon in the frequency transformation stage and demodulator of above-mentioned composition: to the nonlinear elements mixer tube in the frequency transformation stage 8,20, the nonlinearity of the non-linear element detection tube 26 in the demodulator is controlled, thereby makes its circuit gain relevant with nonlinearity that corresponding change take place.

2, receiving system according to claim 1, the nonlinearity of non-linear element is to it is characterized in that by what the amount of negative feedback size of the negative feedback network 9,22,30 that links to each other with element was controlled the dynamic element in the negative feedback network is to be made of diode, the size that changes electric current on the diode 11,28 of flowing through changes the size of diode dynamic electric resistor, or changing the size that is applied to diode 16,19 both end voltage changes the size of diode capacitance, thereby the negative feedback network parameter is changed.

3, receiving system according to claim 1, it is characterized in that the AGC control signal only controls (figure one) to the single nonlinear circuit in the receiving system, also can control (figure two) to a plurality of nonlinear circuits in the device simultaneously, to enlarge the AGC dynamic range.