RU2419192C1 - Differential amplifier with increased amplification factor - Google Patents

Abstract

FIELD: radio engineering. ^ SUBSTANCE: invention can be used as amplification device of analogue signals, in structure of analogue microcircuit chips of various functional purpose (e.g. SiGe-operational amplifiers, comparing units). Differential amplifier includes input differential cascade (DC) (1) with the first (2) and the second (3) current outputs, the first (4) current mirror (CM) the input of which is connected to the first (2) current output of input DC (1), and output is connected to the second (3) current output of input DC (1), output buffer amplifier (5) the output of which is connected to low-resistance load (6). To the circuit there introduced is the second CM (7) and the third CM (8) and additional current-stabilising bipole (CB) (9) connected to input of output buffer amplifier (5), base input of the second CM (7) is connected to the second (3) current output of input DC (1) and the output of the third CM (8) the input of which is connected to output of the second CM (7); at that, common emitter output of the second CM (7) is connected to input of output buffer amplifier (5). ^ EFFECT: increasing amplification factor as to voltage by 8-10 times at using comparatively low-resistance load bipole. ^ 6 dwg

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 of various functional purposes (for example, SiGe-operational amplifiers (op amps), comparators, voltage stabilizers, etc.).

In modern analog microelectronics, two-stage differential amplifiers (DEs) with active loads in the form of current mirrors on bipolar transistors, the type of conductivity of which is opposite to the type of conductivity of the input transistors of the remote control (Fig. 1), are widely used [1-14]. This remote control architecture is quite broadband and is often used in RF and microwave analog devices. However, with low-impedance loads (for example, wave impedances R _n = 50 Ohms), such DEs have low voltage gains (K _y ).

The closest in technical essence to the claimed device is a remote control (figure 1), discussed in US patent firm Sony (Japan) No. 5.144.169, fig.3. It contains the input differential stage 1 with the first 2 and second 3 current outputs, the first 4 current mirror, the input of which is connected to the first 2 current output of the input differential stage 1, and the output is connected to the second 3 current output of the input differential stage 1, output buffer amplifier 5 whose output is associated with a low resistance load 6.

A significant drawback of the known remote control is that when the load is realized in the form of a low-resistance resistor (for example, 50 Ω), its gain is small.

The main objective of the proposed invention is to increase by one or two orders of magnitude the gain in voltage of the remote control when using relatively low-resistance bipolar load (for example, R _n = 50 Ohms).

This object is achieved in that in the differential amplifier of Fig. 1, comprising an input differential stage 1 with first 2 and second 3 current outputs, a first 4 current mirror, the input of which is connected to the first 2 current output of the input differential stage 1, and the output is connected to the second 3 to the current output of the input differential stage 1, the output buffer amplifier 5, the output of which is connected with a low-impedance load 6, new elements and connections are provided - the second 7 and third 8 current mirrors and an additional co-stabilizing two-terminal 9 connected to the input of the output buffer amplifier 5, the basic input of the second 7 current mirror is connected to the second 3 current output of the input differential stage 1 and the output of the third 8 current mirror, the input of which is connected to the output of the second 7 current mirror, the common emitter output of the second 7 of the current mirror is connected to the input of the output buffer amplifier 5.

Figure 1 shows a diagram of the remote control prototype.

A diagram of the inventive device corresponding to the claims is presented in figure 2, and figure 3 - its architecture for the case when the output buffer amplifier is implemented on a transistor with a common emitter.

Figure 4-5 shows a diagram of the remote control prototype (figure 4) and a diagram of the claimed remote control (figure 5) in the Pspice computer simulation environment on models of integrated transistors of the Federal State Unitary Enterprise NPP Pulsar, and figure 6 shows the dependence of the gain according to the voltage of the compared circuits (figure 4, 5) from the frequency. These graphs show that despite the application of a low-impedance load (R _n = 50 Ohms in the circuit of FIG. 5), the voltage gain improves by 40.0 dB (100 times) compared to K of _the known device. This is an important advantage of the proposed remote control.

The differential amplifier with a high gain of Fig. 2 contains an input differential stage 1 with a first 2 and a second 3 current outputs, a first 4 current mirror, the input of which is connected to the first 2 current output of the input differential stage 1, and the output is connected to the second 3 current output of the input differential stage 1, the output buffer amplifier 5, the output of which is connected with a low-impedance load 6. The second 7 and third 8 current mirrors and an additional current-stabilizing two-terminal 9 connected to the input of the output buffer amplifier 5, the basic input of the second 7 current mirror is connected to the second 3 current output of the input differential stage 1 and the output of the third 8 current mirror, the input of which is connected to the output of the second 7 current mirror, and the common emitter output of the second 7 current mirror is connected to the input output buffer amplifier 5.

In the particular case (figure 2), the input differential stage 1 is implemented on the basis of transistors 10, 11 and a two-terminal 12, a current mirror 4 is a transistor 13 and 14, a buffer amplifier is a transistor 15 and a two-terminal 16, a current mirror 7 is a diode 17 and a transistor 18 .

Figure 5 presents the remote control of figure 2, in which the output buffer amplifier 5 is implemented on the transistor 19 and the two-terminal network 20.

Consider the operation of the remote control of figure 2.

The static mode of the transistors 10 and 11 of the remote control of FIG. 2 is set by a two-terminal 12. When introducing a general negative feedback into the remote control of FIG. 2, the static current through its two-terminal 9 is:

where R ₉ is the resistance of the two-terminal 9;

U _{eb. 15%} ≈0.7 V - voltage emitter-base of the transistor 15;

I ₀ - static current of current mirrors 7 and 8.

If the input is Bx. ⁽⁺⁾ 1 a positive voltage u _input 1 is applied, then this causes an increase in the voltage at node 3 (u ₃ ), as well as the voltage at the input of the buffer amplifier 5 (u _{input 5} ) and, as a result, the voltage at the load 6 (u ₆ = u _n ), and

Therefore, the current in the load 6 increases, which leads to a change in the input current i _{5 of the} buffer amplifier 5:

where K _i5 is the current gain of the buffer amplifier 5.

As a result, the total alternating current i _{Σ of the} total emitter circuit of the second 7 current mirror

If we assume that the transmission coefficients of the second 7 and third 8 current mirrors are close to unity, then the difference current i _p , which “loads” the input differential stage 1, will be close to zero:

Or after conversions:

Thus, the equivalent load resistance of the output subcircuit of FIG. 2:

Given that K _i7 ≈1, K _i8 ≈1, we find that in the claimed circuit, the load resistance R ₆ = R _n does not affect the voltage gain K _y

where r _e10 = r _e11 - resistance of the emitter junctions of transistors 10 and 11 of the input differential stage 1.

This allows for higher values of K at small R _{y n} = 10 ÷ 50 ohms.

Thus, the claimed device has significant advantages compared with the prototype.

Information sources

1. US patent No. 4.042.886.

2. Japan patent JP 10032437.

3. Japan patent JP 2005033558.

4. US Patent No. 4,595.883, fig. 4.

5. US patent application No. 2005/0063270 A1, fig.2.

6. US patent No. 5.166.638, fig.1.

7. US patent No. 5.537.081, fig. 3.

8. US patent No. 6.114.904.

9. US patent No. 5.144.169 fig.3.

10. US patent No. 4.223.276.

11. US patent No. 5.365.191, fig. 9.

12. US Patent No. 5.144.259.

13. US patent No. 6.870.426, fig.5.

14. U.S. Patent No. 5.148.121, fig. 1.

Claims (1)

A differential amplifier with an increased gain, comprising an input differential stage (1) with first (2) and second (3) current outputs, a first (4) current mirror, the input of which is connected to the first (2) current output of the input differential stage (1) and the output is connected to the second (3) current output of the input differential stage (1), the output buffer amplifier (5), the output of which is connected to a low-impedance load (6), characterized in that the second (7) and third (8) are introduced into the circuit ) current mirrors and additional current stabilization the two-terminal terminal (9) connected to the input of the output buffer amplifier (5), the basic input of the second (7) current mirror is connected to the second (3) current output of the input differential stage (1) and the output of the third (8) current mirror, the input of which is connected with the output of the second (7) current mirror, and the common emitter output of the second (7) current mirror is connected to the input of the output buffer amplifier (5).

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