CN1411140A

CN1411140A - Computing amplifier capable of operating under low voltage

Info

Publication number: CN1411140A
Application number: CN 01140868
Authority: CN
Inventors: 吴高彬
Original assignee: Elan Microelectronics Corp
Current assignee: Elan Microelectronics Corp
Priority date: 2001-09-25
Filing date: 2001-09-25
Publication date: 2003-04-16
Anticipated expiration: 2021-09-25
Also published as: CN1173464C

Abstract

An operational amplifier with low voltage is to use a common-mode feedback circuit to control voltage level at both ends of its internal differential pair forming a loop with an output level circuit to provide signal output. A current mirror group receives biased current and the branches of which couple to the differential pair and the common mode feedback circuit separately for providing current input. This invention uses a branch of the current mirror group flowing through common feedback circuit and a loop made up differential pair and output level circuit to control its working current and low working voltage is needed.

Description

Computing amplifier capable of operating under low voltage

Technical field

The present invention relates to a kind of operational amplifier, particularly the operation amplifier circuit that can under the low-voltage environment, work.

Background technology

Fig. 1 shows general simulated cushioned level (Buffer), in when work owing to must drive bigger load (big capacitive load or low ohmic load), therefore having very big transient current when transient state flows, based on the consideration of power consumption (efficient), the operational amplifier of the general normal use AB class buffer stage (unity gain buffer) that gains as a whole.

Traditional category-A operational amplifier as shown in Figure 2, transistor Q1～Q5 forms an input stage, transistor Q6 and Q7 are output stage, the operating current Io of output stage is by the decision of the current source of transistor Q7.Because the ability of (sink) of infiltrating is relevant with operating current Io, and transistor Q7 only can provide fixing electric current output, therefore the ability of infiltrating is limited in below the electric current I o.When running into the bigger situation of load, the operating current Io that just must heighten output stage to be obtaining good transient state reaction, but also causes bigger stable state direct current power consumption relatively.

Another kind of operational amplifier can improve above-mentioned shortcoming, AB class operational amplifier as shown in Figure 3, wherein transistor M1～M5 forms input stage, transistor M6 and transistor M7 are output stages, transistor M8 serial connection transistor M9 forms a level shift circuit, and transistor M10～M12 is a bias circuit.Under the situation of stable state, the operating current Io of output stage is determined by aforesaid bias circuit.When transient state, the grid voltage of transistor M6 and M7 all can move simultaneously, makes that transient current can be much larger than operating current Io originally.

Yet the operational amplifier of general A category-B all can face the difficult problem of operating on low voltage, with Fig. 3 is example, its minimum operating voltage will be VTP+2VTN at least, greatly about 2.7～3 volts, such operating voltage is not suitable for two batteries (2.2～3.0V) application scenario, for example LCD panel of mobile phone in the consumer products.

Therefore, be necessary to propose preferable evolutionary approach, in the hope of perfect for operational amplifier.

Summary of the invention

Main purpose of the present invention is to propose a kind of AB class operational amplifier, can be applicable to low voltage operating.

According to the present invention, an operational amplifier comprises that one is differential right, and differential right two outputs and an output-stage circuit form a loop so that signal output to be provided; One common mode feedback circuit is coupled to differential right, to control differential current potential to two outputs; One current source circuit comprises a current source, and it couples a current mirror group, the input of this current mirror group of received electric current, and its branch road be coupled to respectively differential to common mode feedback circuit.The operational amplifier that operating voltage required for the present invention is more traditional is low, and it utilizes the variation of the monitoring of a subcircuits in current mirror group operating voltage, by differential loop to forming with output-stage circuit, makes that operating current can Be Controlled.

Below explain detailedly with the specific embodiment conjunction with figs. so that be easier to understand this present invention's purpose, technology contents, characteristics and effect thereof.

Description of drawings

Fig. 1 represents an analogue buffer;

The category-A operational amplifier that Fig. 2 one is traditional;

The AB class operational amplifier that Fig. 3 one is traditional;

Fig. 4 provides one embodiment of the invention;

Fig. 5 provides an embodiment, cooperates circuit shown in Figure 4 can obtain better effect.

Describe in detail

Fig. 4 provides one embodiment of the invention.Operational amplifier as is well known, transistor O1～O4 forms input stage circuit, wherein transistor O1 with the drain electrode of O2 be coupled in constitute one differential right.The common mode feedback circuit that transistor C1～C4 is formed couples aforementioned differential two right outputs, makes differential two right output end voltage V1 and V2 identical with the input voltage VB of common mode feedback circuit.

The current mirror group that transistor B1～B4 forms couples a current source IR, and wherein transistor B2 is coupled to differential rightly, and transistor B3 is coupled to common mode feedback circuit, and transistor B4 is coupled to the grid of transistor C3, and the electric current I B of the transistor B4 that flows through is relevant with voltage VB.

The output-stage circuit that transistor O5～O8 forms couples differential two right outputs, both and form a loop so that output signal VOUT to be provided.The output signal of the output signal of transistor O5 by transistor O8 be through current mirror O7 counter-rotating gained, operating current Io be subjected to the flowing through control of electric current I B of transistor B4.

The minimum operating voltage of circuit shown in Figure 4 be the threshold voltage VTN of drain electrode-source voltage VDS, transistor C2 of transistor B3 and transistor O6 threshold voltage VTP's and, promptly VTN+VTP+VDS is about 2.0～2.2 volts.

Cooperate circuit shown in Figure 5, the operating voltage of Fig. 4 can be even lower.Current source IR no longer directly is coupled to the current mirror group of transistor B1～B4 in the circuit of Fig. 5, but is connected to the current mirror group of transistor B1～B4 afterwards again through two current mirror groups that transistor A1～A4 forms.Wherein be connected in series a transistor C5 on the path between the current mirror of the current mirror formed of transistor A1 and A2 and transistor A3 and A4 composition, its grid is coupled to common mode feedback circuit.

When the operating voltage step-down, the drain electrode of transistor A2-source voltage VDS diminishes, the electric current of transistor A2 output also diminishes, the current mirror mirror of forming by transistor A3 and A4 subcircuits of transistor B1 in the current mirror group makes the electric current of transistor B2 also diminish, and the electric current I B on the transistor B4 branch road path also diminishes, make current potential VB descend, and then make the operation interval of transistor B3 increase (being that its drain electrode-source voltage can not be extruded).Operating voltage can descend about 0.2～0.3 volt more thus.

Because the combination of Fig. 4 and Fig. 5 circuit, when operating voltage reduced, not only the electric current of transistor B3 can diminish, and transistor B2 electric current also can diminish together.The benefit of doing like this is to keep the current balance type of the input stage circuit of transistor O1～O4, avoids its two output current potential V1 and V2 to rise, and causes the operating circuit Io of output stage to rise simultaneously and produces unusual power consumption situation.

Transistor L1～L5 is a low voltage operating circuit, the electric current of transistor L1 mirrors transistor A2 wherein, and in the present embodiment, the length-width ratio of transistor L1 passage is 1/5 of transistor A2.The electric current of transistor L2 mirrors transistor A3.Transistor L3～L5 forms a current mirror, and wherein transistor L4 and L5 are coupled to differential two right outputs, to control its output end voltage V1 and V2.Continue decline in operating voltage and make the electric current of transistor A2 become at original 1/5 o'clock, transistor L3～L5 begins that current flowing is arranged, and with differential two output end voltage V1 and V2 is pulled down to ground.This practice can prevent the unusual rising of operating current Io of output-stage circuit, and and then shutoff operating current Io.

The above, by embodiment characteristics of the present invention are described, its purpose makes these those skilled in the art can understand content of the present invention and is implementing according to this, and non-limiting claim of the present invention, so, all other do not break away from equivalence variation or the modification that disclosed design is finished, and must be included in the claim scope of the following stated.

Claims

1. computing amplifier capable of operating under low voltage comprises: an input stage circuit comprises that one is differential to receiving inputted signal and two outputs are provided; One common mode feedback circuit, it has a reference node, and described common mode feedback circuit is coupled to described differential right, and is identical with the voltage of described reference node with the voltage level of controlling described differential right two outputs; One current source circuit, comprise that a current source couples a current mirror group, described current mirror group of received reference current, and comprise the first, second, third and the 4th transistor, described transistor seconds couples described differential right, described the 3rd transistor couples described common mode feedback circuit and supplies its required electric current, and described the 4th transistor couples described reference node; And an output-stage circuit, couple described differential two right outputs and form a loop so that signal output to be provided.

2. operational amplifier as claimed in claim 1, wherein said output-stage circuit comprises a current mirror.

3. operational amplifier as claimed in claim 1, wherein said current source circuit also comprise an operating on low voltage circuit, and described operating on low voltage circuit comprises:

First group of current mirror receives described reference current; And

Second group of current mirror, with be connected in series between described first group of current mirror one the monitoring transistor, the transistorized grid voltage of described monitoring is along with the current potential of described reference node changes, and described current source is coupled to described the first transistor through described first group of current mirror and described second group of current mirror.

4. operational amplifier as claimed in claim 3, wherein said operating on low voltage circuit also comprises a low current control loop, to control the current potential of described first output and described second output, described low current control loop detects the output current of described first group of current mirror, when the output of the electric current of described first group of current mirror is reduced to a threshold value, the conducting of described low current control loop pulls down to ground with the current potential of described first output and described second output.

5. operational amplifier as claimed in claim 4, wherein said low current control loop utilizes the output current of the described first group of current mirror of a transistor mirror.