RU2292632C1 - Differential amplifier - Google Patents

Abstract

FIELD: radio engineering; various microelectronic analog-signal amplifiers and converters using low supply voltage.

SUBSTANCE: proposed differential amplifier has differential stages built around transistors 1, 4 and 2, 5, their inputs 3, 6 being connected in parallel, and reference-current supplies 7, 8; collectors of transistors 4, 5 are connected to first common-mode signal inputs 11, 12 of current adder 13 whose output functions as output of differential amplifier 14. Newly introduced in differential amplifier are additional transistors 15, 16 whose bases are connected to integrated emitters of transistors 1, 4 and 2, 5, respectively, emitters are connected to outputs of respective reference-current supplies 7, 8 matched with buses of positive and negative power supplies 9 and 10, respectively. Collector of transistor 15 is connected to input 17 of first current mirror 18 whose output 19 is coupled with emitters of transistors 1, 4, and collector of transistor 16 is connected to input 20 of second current mirror 21 whose output 22 is coupled with emitters of transistors 2, 5.

EFFECT: enhanced attenuation constant of input common-mode signal.

2 cl 10 dwg

Description

The invention relates to the field of radio engineering and communications 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)).

There are known schemes of differential amplifiers (DE), implemented on the basis of two parallel-connected differential stages (DC) with reference current sources in the emitter circuits of input transistors (the so-called "dual input stage") [1-20]. According to this architecture, the modification of which issued about 100 patents of various countries, the operational amplifiers of leading microelectronic companies (AD8631, AD8632, HA2539, etc.) were made. However, in practical circuits of the known DEs, the attenuation coefficient of the input common-mode signal (K _os.sf ) is small (50-60 dB). This is due to the fact that the output resistance of the simplest sources of the reference current based on current mirrors, which provide the widest range of variation of the input common-mode voltage of the DC, is small (30-100 kOhm).

The closest prototype (figure 1) of the claimed device is a differential amplifier described in US patent No. 5.153.529 H 03 f 3/45, containing the first 1 npn and second 2 pnp input transistors, the bases of which are connected to the first 3 input of the differential amplifier, the third 4 npn and fourth 5 pnp input transistors, the bases of which are connected to the second input 6 of the differential amplifier, the first 7 and second 8 reference current sources, coordinated respectively with the bus positive 9 and negative 10 power sources, and the emitters of the first 1 and three its 4 npn input transistors are combined, the second 2 and fourth 5 pnp input transistors are connected to each other, and the collectors of the third 4 pnp and fourth 5 npn input transistors are connected to the first in-phase inputs 11 and 12 of the current adder 13, the output of which 14 is the differential output amplifier. In addition, the collectors of transistors 1 and 2 are connected to the second common-mode inputs of the current adder 13, which provide a phase shift of the signal relative to the first common-mode inputs 11 and 12 by 180 °.

A significant drawback of the known remote control is that it has a low attenuation of the input common-mode signals.

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

This goal is achieved in that in the differential amplifier of figure 1, containing the first 1 npn and second 2 pnp input transistors, the bases of which are connected to the first 3 input of the differential amplifier, the third 4 npn and fourth 5 pnp input transistors, the bases of which are connected to the second input 6 differential amplifiers, the first 7 and second 8 reference current sources, matched respectively with a bus of positive 9 and negative 10 power supplies, the emitters of the first 1 and third 4 npn input transistors combined, the second 2 and the fourth 5 pnp input transistors are connected to each other, and the collectors of the third 4 pnp and fourth 5 npn input transistors are connected to the inputs 11 and 12 of the current adder 13, the output of which 14 is the output of the differential amplifier, new elements and connections between them are introduced (Fig.2 ) - the first pnp 15 and second npn 16 additional transistors are introduced into the circuit, the bases of which are connected respectively to the combined emitters of the first 1 and third 4 input npn transistors and the combined emitters of the second 2 and fourth 5 pnp input transistors, em the terriers are connected to the outputs of the corresponding first 7 and second 8 sources of the reference current, coordinated with the bus of positive 9 and negative 10 power sources, and the collector of the first additional pnp transistor 15 is connected to the input 17 of the first auxiliary current mirror 18, the output 19 of which is connected to the emitters of the first and the third 4 input npn transistors, and the collector of the second additional npn transistor 16 is connected to the input 20 of the second auxiliary current mirror 21, the output of which 22 is connected to the emitters of the second 2 and fourth 5 input pnp transistors.

The diagram of the inventive device in accordance with claim 1 of the claims is shown in figure 2.

Figure 3 shows the directions of currents and voltages of the circuit of figure 2 when applying to the inputs 3 and 6 of the input common-mode signal u _c = u _c1 = u _c2 . In Fig.4 shows a diagram of the remote control of Fig.2 with a specific implementation of the functional units 7, 8, 18, 21, 13.

In Fig.5, the current adder 13 is based on the so-called “bent” cascode.

The scheme of the claimed remote control in accordance with claim 2 of the claims is shown in Fig.6.

7-8 shows a diagram of the remote control prototype of figure 1 in the environment of computer simulation PSpice. Moreover, in the circuit of Fig. 7, real ones are used, and in the circuit of Fig. 8, ideal sources of the reference current 7 (I ₁ ) and 8 (I ₂ ).

Figure 9 shows a diagram of the inventive device (figure 2) in the environment of PSpice.

Figure 1-10 adopted the following notation:

To ₁ - the voltage transfer coefficient of the differential signal of the remote control of Fig.8.

To _y.2 - the transmission coefficient of the voltage of the differential signal of the remote control of Fig.9.

To _y.3 - the transmission coefficient of the voltage of the differential signal of the remote control of Fig.7.

To _sf.1 - the transmission coefficient of the voltage in-phase signal of the remote control Fig.

To _sf.2 - transmission coefficient of voltage in-phase signal of the remote control of Fig.9.

To _sf.3 - transmission coefficient of voltage in-phase signal remote control of Fig.7.

- коэффициент ослабления входного синфазного сигнала.

- attenuation coefficient of the input common mode signal.

The graphs of Fig. 10 characterize the frequency dependence of the differential voltage gains of the control unit of Fig. 7 (prototype) (K _y3 ), the control unit of Fig. 8 (K _y1 ) and the control unit of Fig. 9 of the inventive device (K _y2 ), as well as their common-mode transmission coefficients signal To _{sf. 1} (Fig. 8), To _sf . ₂ (Fig. 9), To _s . ₃ (Fig. 7).

The differential amplifier of figure 2 contains the first 1 npn and second 2 pnp input transistors, the bases of which are connected to the first 3 input of the differential amplifier, the third 4 npn and fourth 5 pnp input transistors, the bases of which are connected to the second input 6 of the differential amplifier, the first 7 and second 8 reference current sources, coordinated respectively with a bus of positive 9 and negative 10 power supplies, the emitters of the first 1 and third 4 npn input transistors are combined, the second 2 and fourth 5 pnp input transistors are connected each other, and the collectors of the third 4 p-n-p and fourth 5 n-p-n input transistors are connected to the first in-phase inputs 11 and 12 of the current adder 13, the output of which 14 is the output of the differential amplifier. The first pnp 15 and second npn 16 additional transistors are introduced into the circuit, the bases of which are connected respectively to the combined emitters of the first 1 and third 4 input npn transistors and the combined emitters of the second 2 and fourth 5 pnp input transistors, the emitters are connected to the outputs of the first 7 and second 8 reference current sources matched with a bus of positive 9 and negative 10 power sources, and the collector of the first additional pnp transistor 15 is connected to the input 17 of the first auxiliary current mirror 18, the output 19 of which is connected to the emitters of the first 1 and third 4 input n-p-n transistors, and the collector of the second additional n-p-n transistor 16 is connected to the input 20 of the second auxiliary current mirror 21, the output 22 of which is connected to the emitters of the second 2 and fourth 5 input p-n-p transistors.

In the differential amplifier of FIG. 6, the current adder 13, in addition to the first common-mode inputs 11 and 12, has second common-mode inputs 23, 24. Moreover, with respect to the first common-mode inputs 11 and 12, the second common-phase inputs 23, 24 provide a 180 ° phase shift of the input signals.

Consider the operation of the claimed remote control of figure 3 (figure 2).

The input common-mode signal u _c = u _c1 = u _c2 with almost a single transmission coefficient is fed to the emitter circuits of differential stages on transistors 1, 4 and 2, 5, as well as the sources of the reference current 7 and 8:

This leads to a change in the output current of the current mirrors 18 and 21 and the emitter currents of the transistors 15 and 16:

where y ₁₈ , y ₂₁ , y ₇ , y ₈ are the output conductivities of current mirrors 18, 21 and reference current sources 7 and 8.

The increments of currents i ₇ and i ₈ are transmitted to the collector circuits of transistors 15 and 16, and then through current mirrors 18 and 21 to the common emitter circuits of differential stages. As a result, the total currents of the common emitter circuits of the DC on transistors 1, 4 and 2, 5:

where K _i18 , K _i21 are the current transfer coefficients of the current mirrors 18 and 21;

α ₁₅ , α ₁₆ - current transfer coefficients of the emitter of transistors 15 and 16.

Or after the transformation (3)

Therefore, the output current of the adder 13, amplified in K _i13 -raz equal

Given that K _i21 ≈α ₁₆ ≈1, from (5) we find that the output current of the remote control due to the presence of in-phase signals 3 and 6 of it

In practical schemes, the reference current source 7 and the current mirror 21, as well as the reference current source 8 and the current mirror 18 are performed according to the same schemes and have the same output transistors and their static mode. As a result, their output conductivities are y ₁₈ = y ₈ , y ₂₁ = y ₇ . Moreover, for the integral npn and pnp transistors of the FSUE NPP Pulsar, the inequalities y ₈ ≪y ₇ , y ₂₁ ≫y _{18 are} satisfied. Therefore, in the claimed remote control, the output signal due to the voltage at the outputs 3 and 6 of the in-phase component of the input voltage is zero, which indicates high values of the attenuation coefficient of the input common-mode signals K _OS.sf. Practically, K _OS.sf. in the claimed control _unit is determined by the non-identity of the resistances of the collector junctions of transistors 1, 4 and 2, 5, which have a 1-2 order less influence on _K.s. Thus, in the remote control of FIG. 2 due to the introduction of new connections, the passage of the common-mode signal to output 14 is significantly weakened. The theoretical conclusions obtained above are confirmed by the results of computer simulation (FIG. 10) of the remote control of FIGS. From the graphs of figure 10 it follows that:

1. The transfer coefficient of the input common-mode signal To _sf.2 in the inventive remote control ( _Fig.9 ) is 40-50 times less than To _sf.3 DU prototype (Fig.7) and is close in magnitude To _sf.1 DU (Fig.8) ) with ideal reference current sources 7 and 8.

2. The transmission coefficients of the differential signal of the claimed remote control and remote control prototype are approximately the same.

3. The attenuation coefficient of the input common-mode signal K _{OS.sf of the} claimed remote control is 50-80 times better than K _{OS.sf of the} remote control prototype.

Bibliographic list

1. RF patent No. 2193273, H 03 F 3/45.

2. Japan Patent No. 53-25232, H 03 F 3/26, 98 (5) A332.

3. Patent US 2001/0052818 A1, H 03 F, 3/45.

4. Japanese Patent No. JP 8222972.

5. Auth. Testimonial. USSR No. 611288.

6. Matavkin V.V. High-speed operational amplifiers. - M.: Radio and Communications, 1989. - p. 103. Figure 6.11.

7. US patent No. 6.366.170 B1, H 03 F / 45.

8. US patent No. 6.268.769, H 03 F / 45.

9. US patent No. 3.974.455, H 03 F / 45.

10. US patent No. 3.968.451, H 03 F / 45.

11. US patent No. 4.837.523, H 03 F / 45.

12. US patent No. 5.291.149, H 03 F / 45.

13. US patent No. 4.636.743, H 03 F / 45.

14. US patent No. 4.783.637, H 03 F / 45.

15. US patent No. 5.515.005, H 03 F / 45.

16. US Patent No. 5.291.149, H 03 F / 45.

17. US patent No. 5.140.280, H 03 F / 45.

18. US patent No. 5.455.535, H 03 F / 45.

19. US patent No. 5.523.718, H 03 F / 45.

20. US patent No. 4.600.893, H 03 F / 45.

Claims (2)

1. A differential amplifier containing the first (1) npn and second (2) pnp input transistors, the bases of which are connected to the first (3) input of the differential amplifier, the third (4) npn and fourth (5) pnp input transistors, the bases of which are connected to the second input (6) of the differential amplifier, the first (7) and second (8) sources of the reference current, coordinated respectively with the bus of positive (9) and negative (10) power sources, and the emitters of the first (1) and third (4) npn input transistors combined, second (2) and fourth (5) pnp input trans the resistors are connected to each other, and the collectors of the third (4) pnp and fourth (5) npn input transistors are connected to the first common-mode inputs (11) and (12) of the current adder (13), the output of which (14) is the output of a differential amplifier, characterized in that the first pnp (15) and second npn (16) additional transistors are introduced into the circuit, the bases of which are connected to the combined emitters of the first (1) and third (4) input npn transistors and the combined emitters of the second (2) and fourth (5 ) pnp input transistors, emitters connected to the outputs Corresponding to the first (7) and second (8) sources of the reference current, coordinated with the bus of positive (9) and negative (10) power sources, the collector of the first additional pnp transistor (15) connected to the input (17) of the first auxiliary current mirror (18) ), the output (19) of which is connected to the emitters of the first (1) and third (4) input npn transistors, and the collector of the second additional npn transistor (16) is connected to the input (20) of the second auxiliary current mirror (21), output (22) which is associated with the emitters of the second (2) and fourth second (5) input p-n-p transistors. 2. The device according to claim 1, characterized in that the collectors of the first npn (1) and second pnp (2) input transistors are connected to the second common-mode inputs (23) and (24) of the current adder (13), which provides a phase shift of the signal relative to the first common-mode inputs (11) and (12) through 180 °.

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