RU2332782C1 - Differential amplifier with increased attenuation of common-mode signal - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: invention can be used as analogue signal amplifying device within various analogue microcircuits (e.g. operational amplifiers (OA), comparators). Differential amplifier (DA) contains the first (1) and the second (2) input transistors (T) with reference power source (3) connected to common emitting circuit, the first (4), the second (5) and the third (6) current mirrors (CM), input of the first CM (4) being connected to collector of the second input of T (2), input of the third CM (6) is connected to collector of the first input of T (1), output of the third CM (6) connected to input of second CM (5), with outputs of the first (4) and the second (5) CM connected to output (7) of DA. Circuit contains the first (8) and the second (9) additional T with their emitting reference transitions parallel to emitting reference transitions of the first (1) and the second (2) inputs of T, the collector of the second additional T (9) being connected to input of additional CM (10), the collector of the first additional T (8) connected to input of the third CM (6) and to output of additional CM (10).

EFFECT: increased attenuation factor of input synphase signals.

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Description

The invention relates to the field of radio engineering and communication and can be used as a device for amplifying analog signals in the structure of analog microcircuits for various functional purposes (for example, operational amplifiers (op amps), comparators).

There are known schemes of push-pull differential amplifiers (DU) based on three current mirrors [1-18], which became the basis of many serial operational amplifiers manufactured both by foreign (CA3080, NA2700 and others), and Russian (K154UD1, etc.) microelectronic companies . Due to the high popularity of such a remote control architecture, more than 50 patents in various countries have been issued for their modification. The alleged invention relates to this subclass of devices.

The closest prototype (figure 1) of the claimed device is a differential amplifier described in US patent No. 5.371.476, containing the first 1 and second 2 input transistors, the common emitter circuit of which includes a reference current source 3, first 4, second 5 and third 6 current mirrors, wherein the input of the first current mirror 4 is connected to the collector of the second input transistor 2, the input of the third 6 current mirror is connected to the collector of the first input transistor 1, the output of the third 6 current mirror is connected to the input of the second current mirror 5, The outputs of the first 4 and second 5 current mirrors are connected to the output 7 of the differential amplifier.

A significant drawback of the known DE is that it does not have a sufficiently high attenuation of common-mode signals (coefficient K _os.sf ), which is associated with an increased influence on the _{K.s. sf of the} output conductivity of the reference current source and the parameters of the current mirrors used.

The main objective of the invention is to increase the attenuation coefficient of the input common-mode signals.

This goal is achieved in that in the differential amplifier of figure 1, containing the first 1 and second 2 input transistors, the common emitter circuit of which includes a reference current source 3, first 4, second 5 and third 6 current mirrors, and the input of the first current mirror 4 connected to the collector of the second input transistor 2, the input of the third 6 current mirror is connected to the collector of the first input transistor 1, the output of the third 6 current mirror is connected to the input of the second current mirror 5, and the outputs of the first 4 and second 5 current mirrors with connected with the output 7 of the differential amplifier, new elements and connections are provided - the first 8 and second 9 additional transistors are introduced into the circuit, the emitter-base junctions of which are connected in parallel with the emitter-base junctions of the first 1 and second 2 input transistors, the collector of the second additional transistor 9 is connected to the input of the additional current mirror 10, and the collector of the first 8 additional transistor is connected to the input of the third current mirror 6 and the output of the additional current mirror 10.

A diagram of the inventive device is shown in figure 2.

Figure 3 and figure 4 presents the scheme of the known (figure 3) and the claimed (figure 4) devices in the environment of computer simulation PSpice on models of integrated transistors of FSUE NPP "Pulsar", and in figures 5-7 - the results of frequency calculations Dependences K _OSF for these circuits for various values of current transfer coefficients (Gain = Ki12 = 0.9-0.99) of current mirrors used.

The differential amplifier of figure 2 contains the first 1 and second 2 input transistors, the common emitter circuit of which includes a reference current source 3, the first 4, second 5 and third 6 current mirrors, the input of the first current mirror 4 being connected to the collector of the second input transistor 2, the input of the third 6 current mirror is connected to the collector of the first input transistor 1, the output of the third 6 current mirror is connected to the input of the second current mirror 5, and the outputs of the first 4 and second 5 current mirrors are connected to the output 7 of the differential amplifier la. The first 8 and second 9 additional transistors are introduced into the circuit, the emitter-base junctions of which are connected in parallel with the emitter-base junctions of the first 1 and second 2 input transistors, the collector of the second additional transistor 9 is connected to the input of the additional current mirror 10, and the collector of the first 8 additional transistor is connected to the input of the third current mirror 6 and the output of the additional current mirror 10.

Consider the operation of the claimed remote control of figure 2. When changing the input common mode signal of the remote control of FIG. 2, u _c = u _c1 = u _c2 changes the current i ₃ in the common emitter circuit of the remote control

where y ₃ is the output conductivity of the reference current source 3.

Current i _{3 is} redistributed between the emitters of transistors 1, 2, 8, 9, so the collector currents of these transistors

where α _i ≈1 is the current gain of the emitter of the i-th transistor.

If you consider that all the current mirrors of the remote control circuitry differ from unity (K _i12 <1), but the transmission coefficients are identical in magnitude, then for the circuit of Fig. 2, we can compose the following system of equations

Substituting formulas (7) and (9) into (10), taking into account (6) and (7), we can find the current increment in the load R _n due to the common-mode signal

where α = α ₁ = α ₂ = α ₈ = α ₉ = ⊥1;

- крутизна передачи синфазного сигнала со входа ДУ фиг.2 на его выход (S_c=0,25y₃К_i12α(1-К_i12)²).

- the steepness of the common-mode signal from the input of the remote control of FIG. 2 to its output (S _c = 0.25y ₃ K _i12 α (1-K _i12 ) ² ).

For the differential input signal u _in = u _c1 -u _c2 the current increment in the load

where S _d - the steepness of the transmission of the differential signal from the input of the remote control of figure 2 to its output.

Thus, the attenuation coefficient of the input common-mode signals of the remote control of figure 2

From the formula (13) it follows that in comparison with the prototype K _{os.sf of the} proposed scheme is significantly increased.

These findings are confirmed by the simulation results of the proposed schemes in the environment of PSpice ( _{Figs. 5-7} ) - the gain in K _{OS.sf of the} remote control of Fig. 2 is from 25 dB to 46 dB, depending on the numerical values of the current transfer coefficient of the current mirrors used.

BIBLIOGRAPHIC LIST

1. US patent No. 4.783.602.

2. US patent No. 4.176.323.

3. US patent No. 5.371.476.

4. US Patent RE 30.587.

5. US Patent No. 4,241.315.

6. US patent No. 4.267.519.

7. US patent No. 4.361.815.

8. US patent No. 3.439.542.

9. US Patent No. 5,880.639.

10. Autost. USSR No. 361605.

11. The patent of Germany No. 2551068.

12. German patent No. 2620999.

13. M. Herpy. Analog integrated circuits. / M. Herpy. - M .: Radio and communications, 1983. - S.185, Fig.5.65.

14. US patent No. 5.936.568.

15. US Patent No. 5,497,124.

16. US Patent No. 3,979.689.

17. US patent No. 5.399.991.

18. US Patent No. 4,618.832.

Claims (1)

A differential amplifier with increased common-mode attenuation, comprising the first (1) and second (2) input transistors whose common emitter circuit includes a reference current source (3), first (4), second (5) and third (6) current mirrors moreover, the input of the first current mirror (4) is connected to the collector of the second input transistor (2), the input of the third (6) current mirror is connected to the collector of the first input transistor (1), the output of the third (6) current mirror is connected to the input of the second current mirror ( 5), and the outputs of the first (4) and second (5) then mirrors are connected to the output (7) of the differential amplifier, characterized in that the first (8) and second (9) additional transistors are introduced into the circuit, the emitter-base junctions of which are connected in parallel with the emitter-base junctions of the first (1) and second (2) input transistors, the collector of the second additional transistor (9) is connected to the input of the additional current mirror (10), and the collector of the first (8) additional transistor is connected to the input of the third current mirror (6) and the output of the additional current mirror (10).

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