RU2393628C1 - Differential amplifier with increased input resistance - Google Patents

Abstract

FIELD: radio engineering.

SUBSTANCE: invention may be used as device for amplification of analog sensor signals with high internal resistance, in structure of analog microchips of various functional purpose (for instance, operational amplifiers (OA), broadband and selective amplifiers, filters, etc.). Differential amplifier (DA) comprises input parallel balance cascade (PBC) (1) on bipolar transistors (T), having the first (2) and second (3) inputs, the first (4) and second (5) main current outputs, connected to load circuit (6), the first (7) and second auxiliary (8) T, bases of which are connected to the first (2) and second (3) inputs of PBC (1), and emitters are connected to each other and connected to output (9) of auxiliary current mirror (T3) (10). PBC (1) comprises the first (11) additional current output, cophased with the first (4) main current output, the second (12) additional current output, cophased with the second (5) main current output, besides the first (11) and second (12) additional current outputs are connected to emitter of additional T (13), base of which is connected to input (14) of CM (10), collector of the first T (7) is connected to the second (3) input of PBC (1), and collector of the second T (8) is connected to the first (2) input of PBC (1).

EFFECT: increased input resistance.

5 cl, 8 dwg

Description

The invention relates to the field of radio engineering and communication and can be used as a device for amplifying analog signals of sensors with high internal resistance, in the structure of analog microcircuits for various functional purposes (for example, operational amplifiers (op amps), broadband and selective amplifiers, filters, etc. )

Known schemes of differential amplifiers (DE) with the parallel inclusion of two parallel-balanced cascades on heterogeneous transistors [1-19]. Over 20 patents have been issued for their modification for leading microelectronic companies in the world. Differential amplifiers of this class, along with single parallel-balanced stages, have become the main amplifying element of many analog interface circuits. The present invention relates to this subclass of devices.

The closest prototype (figure 1) of the claimed device is a differential amplifier, presented in the device according to US patent No. 5.153.529, containing an input parallel-balanced stage 1 on bipolar transistors, having first 2 and second 3 inputs, the first 4 and second 5 main current the outputs associated with the load circuit 6, the first 7 and second 8 auxiliary transistors, the bases of which are connected to the first 2 and second 3 inputs of the input parallel-balanced stage 1, and the emitters are connected to each other and connected to the output 9 of the auxiliary Mirror 10.

This structure of DE is also present in US patents No. 4,555.673, 5.610.557, 4.797.631, 6.963.244, 4.358.739, 5.153.529.

в известных ДУ применяется местная отрицательная обратная связь (вводятся эмиттерные резисторы). Однако при этом ухудшаются многие параметры ДУ - коэффициент усиления по напряжению, напряжение смещения нуля, коэффициент подавления помехи по питанию, крутизна усиления ДУ и др.A significant drawback of the known remote control is that it has a small input differential resistance (R _I ), depending on the absolute values of the current gain of the base (β) of the transistors used and their static mode. For increase

known remote controls use local negative feedback (emitter resistors are introduced). However, at the same time, many parameters of the remote control deteriorate - the voltage gain, the bias voltage, the suppression coefficient of the power supply noise, the gain of the remote control, etc.

The main objective of the invention is to increase by one or two orders of magnitude the input resistance of the remote control without impairing its steepness and a number of other parameters.

This goal is achieved by the fact that in the differential amplifier (figure 1), containing the input parallel-balanced stage 1 on bipolar transistors, having the first 2 and second 3 inputs, the first 4 and second 5 main current outputs associated with the load circuit 6, the first 7 and second 8 auxiliary transistors, the bases of which are connected to the first 2 and second 3 inputs of the input parallel-balanced stage 1, and the emitters are connected to each other and connected to the output 9 of the auxiliary current mirror 10, new elements and communications are provided - the input the parallel-balanced stage 1 contains the first 11 additional current output in phase with the first 4 main current output, the second 12 additional current output in common with the second 5 main current output, the first 11 and second 12 additional current outputs connected to the emitter of the additional transistor 13, the base of which is connected to the input 14 of the auxiliary current mirror 10, the collector of the first 7 auxiliary transistor is connected to the second 3 input of the input parallel-balanced stage 1, and the collector of the second 8 auxiliary nogo transistor 2 is connected to a first input of parallel-to-balanced input stage 1.

Figure 2 presents a diagram of the inventive device in accordance with claim 1 of the claims.

Figure 3 presents a diagram of the inventive device in accordance with claim 2 of the claims.

Figure 4 presents a diagram of the current mirror 10 of the inventive device in accordance with paragraph 4 of the claims.

Figure 5 presents a diagram of the current mirror 10 of the inventive device in accordance with paragraph 5 of the claims.

Figure 6 shows the diagram corresponding to figure 3, in a computer simulation environment PSpice on models of integrated transistors FSUE NLP "Pulsar".

Figure 7 shows graphs of the temperature dependence of the input current of the remote control prototype at R ₃ = 1.1 kOhm and the remote control corresponding to figure 1, which show that at room temperature the proposed device has more than 40 times lower input current.

On Fig shows the frequency dependence of the input resistances of the claimed (Fig.6 with R ₃ = 1.1 kOhm) and known differential amplifiers, from which it follows that the input impedance of the proposed circuit of Fig.6 is 150-200 times greater than in the remote control prototype.

The differential amplifier (figure 2) contains an input parallel-balanced cascade 1 on bipolar transistors, having the first 2 and second 3 inputs, the first 4 and second 5 main current outputs associated with the load circuit 6, the first 7 and second 8 auxiliary transistors, base which are connected to the first 2 and second 3 inputs of the input parallel-balanced stage 1, and the emitters are connected to each other and connected to the output 9 of the auxiliary current mirror 10. The input parallel-balanced stage 1 contains the first AND additional current output, syn common with the first 4 main current output, the second 12 additional current output, in phase with the second 5 main current output, the first 11 and second 12 additional current outputs connected to the emitter of the additional transistor 13, the base of which is connected to the input 14 of the auxiliary current mirror 10, the collector the first 7 auxiliary transistor is connected to the second 3 input of the parallel-balanced input stage 1, and the collector of the second 8 auxiliary transistor is connected to the first 2 input of the parallel-balanced input helmet and 1.

In Fig. 3, in accordance with claim 2, the first 11 and second 12 additional current outputs of the input parallel-balanced stage are connected to the emitter of the additional transistor 13 through an auxiliary two-terminal device 20.

In addition, in accordance with paragraph 3 of the claims, the current transfer coefficient of the auxiliary current mirror 10 of the circuits of FIG. 2 and FIG. 3 is close to two units.

In Fig. 4, in accordance with claim 4, the additional current mirror 10 comprises a first transistor 20, the base of which is connected to the input of the current mirror 14, and the collector with its output 9, an additional pn junction 21, the first 22 and the second 23 auxiliary resistors, the first potential bias circuit based on pn junctions 24, the first auxiliary resistor 22, the first potential bias circuit based on pn junctions 24 and the second auxiliary resistor 23 connected in series, a common node of the first potential bias circuit more pn junctions 24 and the first auxiliary resistor 22 are connected to the emitter of the first transistor 20 and the first output of the additional pn junction 21, the second output of which is connected to the input 14 of the current mirror, and the pn junction area of the transistor 20 is approximately two times the area of the emitter region additional pn junction 21.

In Fig. 5, in accordance with claim 5, the additional current mirror 10 contains second 25 and third 26 transistors, the base of the second transistor 25 is connected to the emitter of the third transistor 26 and the first output of the additional two-terminal 27, the collector of the second transistor 25 is connected to the input the current mirror 14 and the base of the third transistor 26, and the collector of the third transistor 26 is connected to the output of the current mirror 9, the third 28 and fourth 29 additional resistors, and a second potential bias circuit based on pn junctions 30, and the third additional resistor 28, the second potential bias circuit based on pn junctions 30 and the fourth additional resistor 29 are connected in series, and the common node of the second potential bias circuit based on pn junctions 30 and the third additional resistor 28 is connected to the emitter of the second transistor 25 and the second output of the additional bipolar 27.

Consider the operation of the remote control (figure 2).

In the static mode, the static input currents of the remote control I _{input 1} and I _{input 2 are} determined by the difference between the base currents of the input transistors of the differential stage 1 and the collector currents of the transistors 7 and 8:

where I _k7 , I _k8 - collector currents of transistors 7 and 8;

I _l - input static current of cascade 1 at the left input;

I _p - input static current of cascade 1 at its right input.

If we take into account that the current transfer coefficient of the subcircuit 10 is close to two units (K _i12 = 2), and I _l ≈I _к8 = I _p = I ₇ = 2I _b , then it follows from (1) and (2) that the input currents The control of FIG. 2 is close to zero: I _input 1 ≈0, I _input 2 ≈0. This is the first advantage of the proposed scheme.

The second advantage of the proposed device is that in the circuit of figure 2, compensation is provided not only for the static input currents I input ₁ and I _{input 2} , but also their increments i _{input 1} and i _{input 2} . As a result, the input resistance of the remote control of FIG. 2 for alternating current is significantly increased. Indeed, with increasing voltage u _I at input 2 relative to input 3, the base current of each of the two input transistors of cascade 1 connected in parallel increases:

;Where

;

β _1-2 = β ₁ = β ₂ - current gain of the base of the input transistors of the remote control stage 1;

r _e1 , r _e2 - resistance of the emitter transitions in the current base of the input transistors of cascade 1;

φ _t = 25 mV - temperature potential;

I _Σ = 4I ₀ is the total current of the total emitter circuit of the transistors of cascade 1.

Therefore, the variable component of the total base current of the parallel connected input transistors of cascade 1:

On the other hand, the collector current increments of transistors 7 and 8

where r _e8 = r _e7 are the resistance of the emitter junctions of transistors 8 and 7.

Moreover

where I ₉ is the output total current of the current mirror 10.

If we consider that due to the current mirror 10 (K _i12.8 = 2), equality

then equation (6) can be represented as follows

where β ₁₃ is the current gain of the base of the transistor 13.

Therefore, the collector currents of transistors 7 and 8, as well as the total input currents of the remote control i _{input 1} and _input 2 relative to nodes 2 and 3:

where i _l , i _p - variable input currents of the remote control without compensation circuits. After transformations (10) and (11) we find that the input current of node 2

Therefore, the input conductivity of the proposed AC remote control

Since β _1-2 ≈ β ₁₃ , it follows from (13) that in the proposed circuit, _yx significantly decreases (input resistance increases).

In the remote control prototype of FIG. 1, the input conductivity is not better than

Therefore, in the claimed remote control input impedance increases in N _y times, where

The effectiveness of the proposed technical solution substantially depends on the accuracy of the separation of the static current of the common emitter circuit of cascade 1 (I _Σ = 4I ₀ ) between outputs 4 and 11, 5 and 12. If the emitter current of transistor 13 is less than the total current in nodes 4 and 5 of the remote control figure 2, even with β ₁₃ = β _1-2 in the circuit of figure 2 will be observed "undercompensation" of the static input current of cascade 1, since I _k8 <I _l . It should be noted that a strictly specified current division coefficient K _d = I _e13 / I _Σ = 0.5 will be realized only if the static potentials of outputs 4, 11 (12), 5 are the same. If this requirement is not fulfilled, then due to the Earley effect, Kd ≠ 0.5, which somewhat worsens the gain in input resistance and input current. To eliminate this effect, a resistor 20 is introduced in the circuit of FIG. 3, which is selected in such a way as to ensure equality

where U ₄ , U ₅ - voltage at nodes 4, 5;

- напряжение питания;

- supply voltage;

U ₁₄ - static voltage at the input of the current mirror 10;

U _eb.13 - voltage emitter-base of the transistor 13;

R ₂₀ is the resistance of the resistor 20.

The extreme temperature stability of the input static current in the circuit of Fig. 3 is realized in the case when the condition U ₁₁ = U ₄ = U ₅ is satisfied in the entire range of operating temperatures. However, in practical schemes of current mirrors 10, their input static voltage U ₁₃ , as well as voltage U _{eb. 13} , decreases under the influence of temperature, which leads to an imbalance U ₁₁ ≠ U ₄ = U ₅ and, therefore, to the appearance of an additional component drift of the input current of the remote control and the deterioration of the compensation effect R _I. In this regard, in some cases, the authors recommend the use of special current mirrors of Fig. 4 and Fig. 5, in which the voltage at the input U ₁₄ (Fig. 3) is changed due to the diode circuit 24 so that the voltage at the emitter of the transistor 13 and, therefore , the voltage at the outputs 11 and 12 of the remote control of figure 2 (figure 3) was temperature stable. This allows us to obtain the limiting values of the coefficient N _y (15).

The theoretical conclusions obtained above are confirmed by the simulation results of the known and proposed circuits in the PSpice environment on the models of integrated transistors of FSUE NPP Pulsar (Fig. 8). Moreover, the claimed remote control has more than two orders of magnitude better input impedance values. This result is provided without deterioration of other parameters of the remote control slope and zero bias voltage. In addition, the static input currents of the claimed remote control are significantly less than in the scheme of the remote control prototype (Fig.7).

Literature

1. Japanese patent JP 8222972.

2. US Patent Application No. 2004/0174216.

3. US patent No. 6.963.244.

4. US patent No. 6.420.931.

5. US Patent No. 6,222,416.

6. US Patent No. 5,880.639.

7. US Patent No. 5,610.557.

8. US Patent No. 5.153.529.

9. Japanese Patent JP No. 7050528.

10. US patent No. 6.191.619.

11. US patent No. 6.163.290.

12. US Patent No. 5,814.953.

13. US patent No. 5.714.906.

14. US patent No. 5.523.718.

15. US patent No. 5.515.005.

16. US Patent No. 5.293.136.

17. US Patent No. 4,636.743.

18. US patent No. 4.783.637.

19. Matavkin V.V. High-speed operational amplifiers. - M., Radio and Communications, 1989. - S.101-103. - Fig. 6.11 (p. 103).

Claims (5)

1. A differential amplifier with increased input impedance, comprising an input parallel-balanced cascade (1) on bipolar transistors, having first (2) and second (3) inputs, first (4) and second (5) main current outputs connected to the circuit loads (6), the first (7) and second (8) auxiliary transistors, the bases of which are connected to the first (2) and second (3) inputs of the input parallel-balanced stage (1), and the emitters are connected to each other and connected to the output (9) auxiliary current mirror (10), characterized in that the input parallel -balanced stage (1) contains the first (11) additional current output, in phase with the first (4) main current output, the second (12) additional current output, in phase with the second (5) main current output, the first (11) and second (12) additional current outputs are connected to the emitter of an additional transistor (13), the base of which is connected to the input (14) of the auxiliary current mirror (10), the collector of the first (7) auxiliary transistor is connected to the second (3) input of the parallel-balanced input stage ( 1), and the collector of the second (8) auxiliary atelnogo transistor connected to the first (2) input of parallel-to-balanced input stage (1). 2. The differential amplifier according to claim 1, characterized in that the first (11) and second (12) additional current outputs of the input parallel-balanced stage are connected to the emitter of the additional transistor (13) through an auxiliary two-terminal device (20). 3. The device according to claim 1, characterized in that the current transfer coefficient of the auxiliary current mirror (10) is close to two units. 4. The differential amplifier according to claim 1, characterized in that the additional current mirror (10) contains a first transistor (20), the base of which is connected to the input of the current mirror (14), and the collector with its output (9), an additional pn junction (21), the first (22) and second (23) auxiliary resistors, the first potential bias circuit based on pn junctions (24), the first auxiliary resistor (22), the first potential bias circuit based on pn junctions (24) and the second auxiliary resistor (23) connected in series, common node of the first bias circuit potentials based on pn junctions (24) and the first auxiliary resistor (22) is connected to the emitter of the first transistor (20) and the first output of the additional pn junction (21), the second output of which is connected to the input (14) of the current mirror, and the area pn the transition of the transistor (20) is approximately two times larger than the area of the emitter region of the additional pn junction (21). 5. The differential amplifier according to claim 1, characterized in that the additional current mirror (10) contains the second (25) and third (26) transistors, the base of the second transistor (25) is connected to the emitter of the third transistor (26) and the first output of the additional two-terminal device (27), the collector of the second transistor (25) is connected to the input of the current mirror (14) and the base of the third transistor (26), and the collector of the third transistor (26) is connected to the output of the current mirror (9), the third (28) and fourth (29) ) additional resistors, and a second potential bias circuit based on pn per moves (30), with the third additional resistor (28), the second potential bias circuit based on pn junctions (30) and the fourth additional resistor (29) connected in series, and the common node of the second potential bias circuit based on pn junctions (30) and the third additional resistor (28) is connected to the emitter of the second transistor (25) and the second output of the additional two-terminal device (27).

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