RU2441316C1 - Differential amplifier with low supply voltage - Google Patents

Abstract

FIELD: radio engineering. ^ SUBSTANCE: differential amplifier with low supply voltage comprises from the first to the fourth input transistors, the first and second current-stabilising dipoles, the first and second load dipoles, the first and second current mirrors. ^ EFFECT: increased coefficient of DA input cophased signals suppression at relatively low resistances of the first and second current-stabilising dipoles. ^ 7 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, in operational amplifiers (op amps), comparators, etc.).

There are known schemes of differential amplifiers (DE) based on two differential stages (DC) parallel-connected at the inputs with current-stabilizing two-terminal circuits in the emitter circuits of input transistors (the so-called "dual input stage"). Remote controls with such an architecture have become the basis for the construction of many modern operational amplifiers both on bipolar [1-17] and field [16-28] transistors. However, such remote controls do not have a sufficiently high attenuation of the input common-mode signals when passive elements (resistors) are used as current-stabilizing two-terminal devices, which negatively affects the accuracy of analog interfaces with their use. This is due to the fact that in order to obtain large values of the attenuation coefficient of the input common-mode signals (K _os.sf ), it is necessary to choose the resistance of the current-stabilizing resistors at the level of hundreds of kilo-ohms, which creates problems with the static mode at low-voltage power supply (E _p = 1.5 ÷ 2, 5 B). On the other hand, at supply voltages E _p = ± 1 V, the only way to stabilize the DC static mode is to use low-resistance resistors as current-stabilizing two-terminal devices, since with other versions of their construction, for example, in the form of transistor current sources, the required supply voltage must be at least 1.4 V.

The closest prototype (figure 1) of the claimed device is a differential amplifier described in US patent No. 5225791, fig.2, containing the first 1 and second 2 input transistors, the combined emitters of which are connected through the first 3 current-stabilizing bipolar to the first 4 bus power source, base connected to the corresponding first 5 and second 6 inputs of the device, the collector of the first 1 input transistor is connected to the first 8 output of the device and through the first 9 two-pole load connected to the second 10 bus power source, collect The second 2 output transistor is connected to the second 11 output of the device and through the second 12 the load two-pole terminal is connected to the second 10 power supply bus, the third 13 and fourth 14 input transistors, the combined emitters of which are connected to the second 10 power supply bus through the second 15 current-stabilizing resistor, base the third 13 output transistor is connected to the first 5 input of the device, the base of the fourth 14 input transistor is connected to the second 6 input of the device, the first 1 and third 13 input transistors, as well as the second 2 and the fourth 14 input transistors are opposed conductivity types.

A significant drawback of the known remote control is that it has a low attenuation of the input common-mode signals. First of all, this drawback is manifested when using resistors or the simplest current sources on Erly low voltage transistors as the first 3 and second 15 two-terminal circuits, which have a small output resistance (about 20-30 kOhm) at milliampere currents.

The main objective of the invention is to increase the attenuation coefficient of the input common-mode signals DU (K _OSF ) with relatively small resistances of the first 3 and second 15 current-stabilizing two-terminal devices. At the same time, in the claimed control unit, relatively low-resistance resistors (units of kilo-ohms) can be used as current-stabilizing two-terminal 3 and 15 with low-voltage power supply. Nevertheless, this does not significantly affect the numerical values of its K _os.sf.

The problem is solved in that in the differential amplifier with a low supply voltage of Fig. 1, containing the first 1 and second 2 input transistors, the combined emitters of which are connected through the first 3 current-stabilizing two-terminal devices to the first 4 bus of the power supply, the bases are connected to the corresponding first 5 and second 6 inputs of the device, the collector of the first 1 input transistor is connected to the first 8 output of the device and through the first 9 two-terminal load connected to the second 10 bus of the power source, the collector of the second 2 output the transistor is connected to the second 11 output of the device and through the second 12 the bipolar load is connected to the second 10 power supply bus, the third 13 and fourth 14 input transistors, the combined emitters of which are connected to the second 10 power supply bus through the second 15 current-stabilizing resistor, the base of the third 13 output transistor connected to the first 5 input of the device, the base of the fourth 14 input transistor is connected to the second 6 input of the device, the first 1 and third 13 input transistors, as well as the second 2 and fourth 14 input the transistors have the opposite types of conductivity, new elements and connections are provided - the first 16 and second 17 current mirrors are matched to the first 4 bus of the power supply, the input of the first 16 current mirror is connected to the collector of the third 13 input transistor, the output of the first 16 current mirror is connected with the second 11 output of the device, the input of the second 17 current mirror is connected to the collector of the fourth 14 input transistor, and the output of the second 17 current mirror is connected to the first 8 output of the device.

In Fig.1 shows a diagram of the remote control prototype, and in Fig.2 - the claimed remote control. Alternating currents and voltages in the claimed remote control when exposed to its inputs Bx.1 (5) and Bx.2 (6) in-phase signal u _с1 = u _c2 = u _c are shown in Fig.3.

Figure 4 shows the scheme of the remote control prototype of figure 1 on SiGe models of integrated transistors at a supply voltage of ± 1 V, which was studied by the authors in the Cadence environment for the attenuation of input common-mode signals u _c1 = v4 = u _c , u _c2 = v ₇ = u _c .

Figure 5 shows a diagram of the claimed remote control of figure 2 (when exposed to its inputs in-phase signal u _c ) on SiGe models of integrated transistors with a supply voltage of ± 1 V.

Figure 6 shows the frequency dependence of the gain on the voltage of the input signal (K _y ) of the compared circuits of figure 4 and figure 5.

Figure 7 shows the frequency dependence of K _OS.sf compared schemes of remote control.

The differential amplifier with a low voltage of FIG. 2 and FIG. 3 contains first 1 and second 2 input transistors, the combined emitters of which are connected through the first 3 current-stabilizing two-terminal devices to the first 4 bus of the power source, the bases are connected to the corresponding first 5 and second 6 inputs of the device, the collector of the first 1 input transistor is connected to the first 8 output of the device and through the first 9 two-pole load connected to the second 10 bus of the power source, the collector of the second 2 output transistor is connected to the second 11 by the device’s progress and through the second 12, the two-pole load is connected to the second 10 power supply bus, the third 13 and fourth 14 input transistors, the combined emitters of which are connected to the second 10 power supply bus through the second 15 current-stabilizing resistor, the base of the third 13 output transistor is connected to the first 5 input devices, the base of the fourth 14 input transistor is connected to the second 6 input of the device, the first 1 and third 13 input transistors, as well as the second 2 and fourth 14 input transistors, are opposite types of conductivity. The first 16 and second 17 current mirrors are aligned with the first 4 bus of the power source, the input of the first 16 current mirror is connected to the collector of the third 13 input transistor, the output of the first 16 current mirror is connected to the second 11 output of the device, the input of the second 17 current mirror is connected to the collector of the fourth 14 input transistor, and the output of the second 17 current mirrors is connected to the first 8 output of the device.

As current mirrors 16 and 17, many classical solutions can be used that provide inverting current gain with a current gain of K _i16 = K _i17 = -1.

Consider the work of the claimed remote control of figure 2.

The basic equations for static currents and voltages in the remote control of figure 2 with U _c1 = U _c2 = 0 are:

,

- напряжения питания;Where

,

- supply voltage;

U _pt17 , U _pt16 - voltage on current mirrors;

U ₁₅ , U ₉ , U ₃ - voltage across the resistors 15, 9, 3;

U _e.i - voltage emitter-base transistors;

U _kb.i - collector-base voltage of transistors.

From (1) the main restrictions on the supply voltage in the remote control of figure 2 follow:

From the last equations, you can find the maximum amplitudes of the output voltages of the remote control of figure 2:

Changing the input common-mode voltage at the inputs of the remote control 5 and 6 of figure 3 by the value of u _c = u _c = u _c2 leads to a change in currents through the two-terminal networks 15 and 3:

where y ₁₅ , y ₃ - conductivity of two-terminal networks 15 and 3;

i ₀ = 0.5i ₁₅ = 0.5i ₃ .

Therefore, the collector currents of transistors 1 and 2, 13 and 14:

where α _i ≈1 are the current transfer coefficients of the emitter of transistors 1, 2, 13, 14.

The collector currents of transistors 13 and 14 i _k13 , i _k14 are transmitted through current mirrors 16 and 17 to the outputs of the remote control 8, 11 and create two current components in the load resistors 9 and 12:

where K _i12.16 = K _i12.17 = -1 - current transfer coefficient of current mirrors 16 and 17.

Moreover, the directions of these currents in the two-terminal networks 9 and 12 are opposite to the directions of the currents i _k1 and i _k2 . Therefore, in the output nodes of the remote control 8 and 17 there is a pairwise mutual compensation of the common-mode components of the gain error:

Therefore, the voltage at the outputs of the remote control and the transfer coefficient of the common mode signal

,

- коэффициенты передачи синфазного сигнала ДУ-прототипа. ПричемWhere

,

- transmission coefficients of the in-phase signal of the remote control prototype. Moreover

From (13) - (17) it follows that the proposed remote control has, for example, for output 11 lower (Nc-times) values of the common-mode signal transfer coefficient, where

If we take into account that α ₁₃ ≈α ₂ , K _i12.16 = 1, then when choosing R ₃ = R ₁₅ we get that in the proposed control factor N _c >> 1.

The differential voltage transfer coefficient (K _y ) in the remote control of FIG. 3 is two times greater than in the remote control prototype (FIG. 6). In this case, the upper cutoff frequency K _y improves two times (f _in = 17.7 GHz).

Thus, the gain in the attenuation coefficient of the input common-mode signals (K _OS.sf ) in the remote control of _figure 2

- коэффициент К_ос.сф.2 ДУ-прототипа для выхода 11.Where

- coefficient K _OS.sf.2 DU prototype for output 11.

These findings are confirmed by the results of computer modeling of the compared circuits (Fig. 7), which show that the proposed remote control has more than 50 dB better attenuation of input common-mode signals. This is enough for its many applications.

Thus, in contrast to the known remote control, the proposed circuit has significant advantages and can provide a relatively large attenuation of the input common-mode signals at low supply voltages (E _p = ± 1 V).

BIBLIOGRAPHIC LIST

1. Patent application JP 2004/129018.

2. Patent SU No. 530425.

3. US patent No. 4649352.

4. US patent No. 5153529.

5. US patent No. 5225791.

6. US patent No. 5291149, fig. 1.

7. US patent No. 5420540.

8. US Patent No. 5515005, fig. 2.

9. US Patent No. 6222416, fig. 2.

10. US Patent No. 3974455, fig. 7.

11. US Patent No. 4349786.

12. US patent No. 4636743.

13. US patent No. 4783637.

14. US patent No. 5293136.

15. US patent No. 6366170.

16. US Patent No. 6136290.

17. US patent No. 6288769.

18. US patent No. 5909146.

19. Patent application JP 2004/222104.

20. US patent No. 6801087.

21. US patent No. 5917378.

22. US Patent Application 2008/0074405.

23. Patent application US 2009/0206930.

24. US patent No. 6356153.

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28. US patent No. 6731169.

Claims (1)

A differential amplifier with a low voltage, containing the first (1) and second (2) input transistors, the combined emitters of which are connected through the first (3) current-stabilizing two-terminal to the first (4) bus of the power supply, the bases are connected to the corresponding first (5) and second (6) the inputs of the device, the collector of the first (1) input transistor is connected to the first (8) output of the device and through the first (9) two-terminal load connected to the second (10) bus of the power source, the collector of the second (2) output transistor is connected to the second ( 11) the output of the device and through the second (12) two-pole load connected to the second (10) bus power supply, the third (13) and fourth (14) input transistors, the combined emitters of which are connected to the second (10) bus power supply through the second (15 ) a current-stabilizing resistor, the base of the third (13) output transistor is connected to the first (5) input of the device, the base of the fourth (14) input transistor is connected to the second (6) input of the device, the first (1) and third (13) input transistors, and also the second (2) and fourth (14) input transistors have the opposite types of conductivity, characterized in that the first (16) and second (17) current mirrors are matched to the first (4) bus of the power source, the input of the first (16) current mirror is connected to the collector of the third (13) input transistor , the output of the first (16) current mirror is connected to the second (11) output of the device, the input of the second (17) current mirror is connected to the collector of the fourth (14) input transistor, and the output of the second (17) current mirror is connected to the first (8) output of the device .

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