RU2293433C1 - Differential amplifier with increased weakening of input cophased signal - Google Patents

Abstract

FIELD: radio engineering and communications, possible use as amplification device for analog signals in structure of analog microchips of various functional purpose.

SUBSTANCE: amplifier (dwg.2) contains input parallel-balanced cascade 1 with first 2 source of supporting current in common emitter chain, output of which 3 is connected to input of current mirror 4, auxiliary transistor 5, collector of which is connected to output of current mirror 4, and to output 6 of differential amplifier, while emitter is connected to second 7 source of bearing current, first source of supporting current 2 in common emitter circuit of input parallel-balance cascade 1 is connected to base of auxiliary transistor 5.

EFFECT: increased coefficient of weakening of cophased input signal.

3 cl, 13 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)).

Known schemes of classical differential amplifiers (DE), implemented on the basis of the classic parallel-balanced cascade with a reference current source in the common emitter circuit of the input transistors and a current mirror, the output of which is connected to the load [1-9]. Such remote controls have become one of the main elements of modern analog microcircuitry widely used in the structure of various precision voltage-current converters and operational amplifiers. A significant drawback of such remote controls is that they have low values of the attenuation coefficient of the input common-mode signal (K _OS.sf ), which substantially depends on the output resistance of the reference current source.

The closest prototype (figure 1) of the claimed device is a differential amplifier described in US patent No. 4.264.873, containing an input parallel-balanced cascade 1 with the first 2 reference current source in a common emitter circuit, the output of which 3 is connected to the input of the current mirror 4, auxiliary transistor 5, the collector of which is connected to the output of the current mirror 4 and the output 6 of the differential amplifier, and the emitter is connected to the second 7 source of the reference current. The sources of the reference current 2 and 7 have respectively output conductivities of ₂ and ₇ . The base of the transistor 5 is connected to a reference voltage source E _c1 .

A significant drawback of the known remote control (figure 1) 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 (K _OS.sf ).

This goal is achieved by the fact that in the differential amplifier (figure 1), containing an input parallel-balanced stage 1 with the first 2 reference current source in the common emitter circuit, the output of which 3 is connected to the input of the current mirror 4, an auxiliary transistor 5, the collector of which is connected to the output of the current mirror 4 and the output 6 of the differential amplifier, and the emitter is connected to the second 7 source of the reference current, new connections are introduced - the first source of the reference current 2 in the common emitter circuit of the input parallel-balanced stage 1 Knit with the base of the auxiliary transistor 5. In the particular case parallel to the first reference current source 2 is turned on the third reference current source 8, identical to the first 2 and the second reference current source 7.

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

Figure 3 shows the claimed remote control in accordance with paragraph 2 of the claims, and figure 4 is a specific implementation of the remote control of figure 3. Here, the sources of the reference current 2, 7 and 12 are implemented on the corresponding bipolar transistors, the static mode of which is set by the two-terminal I ₀ .

The remote control circuit in accordance with claim 3 of the claims is presented in FIG. 5, and FIG. 6 shows a specific embodiment of an additional voltage follower 13.

The results of computer simulation of the remote control of FIG. 1, FIGS. 4 and 5 in the PSpice environment with differential and common-mode input signals on the models of integrated transistors of the Federal State Unitary Enterprise NPP “Pulsar” and the parameters of the elements (modes) indicated in FIG. 7 (the claimed remote control is FIG. 5 ), Fig. 8 (prototype - Fig. 1), Fig. 9 (claimed DU - Fig. 5), Fig. 10 (prototype - Fig. 1) are shown in Figs. 11, 12 and 13. Moreover:

- Fig.7 is a diagram of the claimed remote control when applying to its inputs a differential signal u _ac.1 = u _in ;

- Fig. 8 is a diagram of the remote control of the prototype when applying a differential signal u _ac.2 = u _in to its inputs;

- Fig.9 is a diagram of the claimed remote control (Fig.5) when applying in-phase signal to its inputs;

- figure 10 is a diagram of the remote control of the prototype (figure 1) when applying to its inputs in-phase signal;

- Fig.11 - the amplitude-frequency characteristic of the slope (S _DC ) of the conversion of the input differential voltage of the claimed remote control (Fig.7) and the remote control of the prototype (Fig.8) in their output currents;

- Fig.12 - amplitude-frequency characteristics of the slope of the conversion (S _cc ) of the input common-mode voltage of the claimed remote control (Fig.9) and the remote control of the prototype (Fig.10) into their output currents. Moreover, the measurements were carried out when applying to the base of the input transistors of the remote control relative to the common bus of the same voltage u _c1 = u _c2 = u _c = u _ac ;

- Fig.13 is a frequency dependence of the attenuation coefficient of the input common-mode voltage of the claimed (Fig.7, 9) and known (Fig.8, 10) amplifiers.

In Figs. 7-13 and in the text of the description, the following designations of the parameters of the remote control and circuit elements are adopted:

To _beats - the transmission coefficient of the differential input voltage of the remote control u _I ;

To _us - the transfer coefficient of the common-mode input voltage u _c .

Moreover, between these parameters and the attenuation coefficient of the input common-mode signals K _OS.sf there is the following relationship

where u _I - voltage between the inputs of the remote control;

u _c - common-mode input voltage at the inputs of the remote control;

u _o - remote control output voltage (u _o = i _o R _n );

R _n - load resistance connected to the output of the remote control;

S _ds - the steepness of transmitting remote control by differential input signal u _I ;

S _cc is the steepness of the remote control transmission by the in-phase input signal u _c ;

C ₁ = C ₂ = C _s is the capacitance on the substrate of the transistors of the sources of the reference current.

The differential amplifier (figure 2) contains an input parallel-balanced stage 1 with the first 2 source of the reference current in a common emitter circuit. The output 3 of cascade 1 is connected to the input of the current mirror 4, and the collector of the auxiliary transistor 5 is connected to the output of the current mirror 4 and the output 6 of the differential amplifier, and the emitter is connected to the second 7 reference current source. The first reference current source 2 in the common emitter circuit of the input parallel-balanced stage 1 is connected to the base of the auxiliary transistor 5. The inputs 8 and 9 of the remote control (Fig. 2) are the bases of transistors 10 and 11.

In accordance with claim 2 of the claims (FIG. 3), a third 12 reference current source is included in parallel with the first 2 reference current sources, identical to the first 2 and second 7 reference current sources.

In accordance with paragraph 3 of the claims (figure 5), the first 2 source of the reference current in the common emitter circuit of the input parallel-balanced stage 1 is connected to the base of the auxiliary transistor 5 through an additional voltage follower 13, which in a particular case is made on the transistor 14 and the two-terminal 15 (Fig.6).

Consider the operation of the claimed remote control by the example of circuit analysis (figure 3).

If the inputs 8 and 9 of the remote control (Fig. 3) are supplied with a common-mode input voltage u _c = u _c1 = u _c2 , then in the output conductivities of ₂ , ₇ , ₁₂ sources of the reference current I ₂ = I ₇ = I ₁₂ = I ₀ variable components will appear

The increments of currents i ₁₂ , i ₂ enter the common emitter circuit of the differential stage 1 and are divided in half. As a result, the collector current of transistor 11 (output current 3) and output current i _{4 of} current mirror 4

where α ₁₁ ≈1 is the current gain of the emitter of transistor 11;

K _i ≈1 is the current gain of the current mirror 4.

On the other hand, the collector current of the transistor 5

Thus, in the output circuit 6 of the claimed remote control there is a mutual compensation of two close in magnitude currents i _k5 and i ₄ due to the presence at its inputs 8 and 9 of the in-phase component of the input signal u _c :

In view of (1) and (4), from (5) we can find that

Moreover, the steepness of the common-mode signal transmission and the transfer coefficient u _c to the remote control output (figure 3)

where R _n is the load resistance of the remote control.

The transmission coefficient of the remote control (figure 3) on the differential input

where r _e10 , r _e11 - resistance of the emitter junctions of transistors 10 and 11;

φ _t ≈25 mV - temperature potential;

I ₀ = I ₂ = I ₇ = I ₁₂ .

In the claimed circuit in accordance with P2 of the claims, due to the integrated manufacturing technology of transistors and circuitry, a high identity of the output conductivities of the applied sources of the reference current 2, 7 and 12 is ensured: y ₂ = y ₁₂ = y ₇ = y ₀ .

therefore

where I ₀ = I ₂ = I ₁₂ = I ₇ , y ₀ = y ₂ = y ₁₂ = y ₇ .

Since K _i = 1, α ₁₁ = α ₅ ≈1, it follows from formula (12) that K _os.sf in the claimed control _unit increases N times (compared to the control unit prototype - figure 1), where

Real values of N reach one or two orders of magnitude (N = 10 ÷ 100 times).

The analytical conclusions obtained above are confirmed by the results of modeling the proposed circuits in the PSpice environment using the integrated transistor models of the Federal State Unitary Enterprise NPP Pulsar (Moscow).

The attenuation coefficient of the in-phase input signal of the remote control (Fig. 5, 7) exceeds the value of K _OS.sf > 94 dB in a fairly wide frequency range (Fig. 13). At the same time, in the claimed remote control (FIGS. 5, 7), the frequency range for the differential signal (FIG. 11) is expanded from 482 to 745 MHz.

In comparison with the remote control prototype (Fig. 1, 8), which has a _K.s.sf = 63 dB up to a frequency of 2.4 MHz, the claimed remote control allows you to get a wider frequency range (f _vs = 30.7 MHz) with the same attenuation of the common mode signal (Fig.13).

In the considered remote control scheme (Figs. 2, 3, 4 and 5), a high degree of parametric compensation of the influence of temperature and radiation on the emf is also provided. zero bias due to the bias of the input and output characteristics of the transistors of the reference current sources 2, 7, 12.

If the power supply voltage of the remote control and, as a consequence, the current I _o change (Fig. 4), then the suppression coefficient of the power supply noise also decreases in the inventive device.

Information sources

1. Polonnikov D.E. Operational amplifiers: principles of construction, theory, circuitry. - M., 1983.

2. US patent No. 4.264.873, H 03 F 3/45.

3. US patent No. 5.365.191, H 03 F 3/45.

4. US patent No. 5.936.468, H 03 F 3/45.

5. US patent No. 5.551.005, H 03 F 3/45.

6. US patent No. 4.783.637, H 03 F 3/45.

7. US patent No. 5.291.149, H 03 F 3/45.

8. Japanese Patent JP 2004, 040157, H 03 F 3/45.

9. Japanese Patent JP 7050528, H 03 F 3/45.

Claims (3)

1. A differential amplifier with increased attenuation of the input common-mode signal, comprising an input parallel-balanced stage (1) with the first (2) reference current source in the common emitter circuit, the output of which (3) is connected to the input of the current mirror (4), an auxiliary transistor ( 5), the collector of which is connected to the output of the current mirror (4) and the output (6) of the differential amplifier, and the emitter is connected to the second (7) reference current source, characterized in that the first reference current source (2) in the common emitter circuit is input parallel -ba ansnogo stage (1) is connected to the base of the auxiliary transistor (5). 2. The device according to claim 1, characterized in that a third (12) reference current source is identical to the first (2) and second (7) reference current sources in parallel with the first (2) reference current source. 3. The device according to claim 1, characterized in that the first (2) source of the reference current in the common emitter circuit of the input parallel-balanced stage (1) is connected to the base of the auxiliary transistor (5) through an additional voltage follower (13).

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