RU2416147C1 - Differential amplifier with increased amplification factor - Google Patents

Abstract

FIELD: radio engineering.

SUBSTANCE: differential amplifier includes input differential cascade (DC) (1) with the first (2) and the second (3) current outputs connected to the first bus (4) of power supply (PS) through the first (5) and the second (6) load bipoles, the first (7) and the second (8) output transistors (T) the bases of which are combined, collectors are connected to the appropriate first (2) and second (3) current outputs of DC (1), and emitters are connected to the second bus (9) of PS, buffer amplifier (10) the input of which is connected to the second (3) current output of DC (1). To the diagram there introduced are the first (11) and the second (12) additional T the emitters of which are connected to the first additional current-stabilising bipole (CB) (13), bases are connected to the appropriate first (2) and the second (3) current outputs of DC (1), collector of T (12) is connected through the second CB (14) to the first bus of (4) PS and to input of additional non-inverting amplifier the output of which is connected to combined bases of the first T (7) and the second T (8).

EFFECT: increasing amplification factor as to voltage by 8-10 times at using low-resistance load bipoles.

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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, SiGe-operational amplifiers (op amps), comparators).

In modern analog microelectronics, differential amplifiers (DE) 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, are widely used. However, the SiGe technical process SGB25VD, which is currently being implemented in a number of Russian enterprises for the production of new generation CEA, does not provide the possibility of constructing circuits with pnp transistors. This does not allow the use of traditional active loads in the op amp microwave range. As a result, as the elements of the collector circuit of the input stage of the op amp, it is very often allowed to use only passive elements - resistors [1-25]. Ultimately, this requirement limits the voltage gain (K _y ) of the op-amp input differential stage and the entire op-amp circuit as a whole.

The closest in technical essence to the claimed device is a remote control (figure 1), discussed in US patent No. 4.418.290. It contains the input differential stage 1 with the first 2 and second 3 current outputs connected to the first 4 bus of the power supply through the first 5 and second 6 two-pole load, the first 7 and second 8 output transistors, the bases of which are combined, the collectors are connected to the corresponding first 2 and the second 3 current outputs of the input differential stage 1, and the emitters are connected to the second 9 bus of the power source, a buffer amplifier 10, the input of which is connected to the second 3 current output of the input differential stage 1.

A significant drawback of the known remote control is that when the implementation of bipolar load 5 and 6 in the form of low-resistance resistors (500-1000 Ohms), its gain is small.

The main objective of the proposed invention is to increase by 8-20 times the voltage gain when using low-resistance bipolar load (for example, R ₅ = R ₆ = 700 Ohms).

The problem is achieved in that in the differential amplifier of Fig. 1, containing an input differential stage 1 with a first 2 and a second 3 current outputs connected to the first 4 bus of the power supply through the first 5 and second 6 two-pole load, the first 7 and second 8 output transistors whose bases are combined, the collectors are connected to the corresponding first 2 and second 3 current outputs of the input differential stage 1, and the emitters are connected to the second 9 bus of the power source, a buffer amplifier 10, the input of which is connected to the second m 3 by the current output of the input differential stage 1, new elements and connections are provided - the first 11 and second 12 additional transistors are introduced into the circuit, the emitters of which are connected to the first 13 additional current-stabilizing two-terminal devices, the bases are connected to the corresponding first 2 and second 3 current outputs of the input differential stage 1, the collector of the second 12 additional transistor is connected through the second 14 additional current-stabilizing two-terminal with the first 4 bus power supply and connected to the input of the additional solid non-inverting amplifier 15, the output of which is connected to the combined bases of the first 7 and second 8 output transistors.

A diagram of the inventive device corresponding to the claims is shown in figure 2. Figure 3, 4 shows special cases of the implementation of additional non-inverting amplifier 15.

Figure 5 - 6 shows a diagram of the remote control prototype (figure 5) and

the scheme of the claimed remote control (Fig.6) in the Cadence computer simulation environment on IHP integrated transistor models, and Fig.7 shows the voltage gain of the compared circuits (Fig.5, 6) without frequency correction elements. These graphs show that despite the use of low-resistance bipolar loads 5 and 6 (R ₅ = R ₆ = 600 Ohms), the voltage gain of the proposed remote control improves by more than an order of magnitude (29.0 dB) compared to K of _the known device. This is an important advantage of the proposed remote control when it is implemented as part of the SGB25VD process.

On Fig shows the dependence of the gain on the voltage of the compared circuits (figure 5, 6) with the elements of the frequency correction (With _cor = 4 pF).

Figure 9 shows the dependence of the voltage gain on the compared circuits (Figs. 5, 6) with 100% negative feedback without frequency correction elements.

Figure 10 shows the dependence of the voltage gain of the compared circuits (Figs. 5, 6) with 100% negative feedback from the frequency correction element (C _cor = 4 pF).

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 connected to the first 4 bus of the power supply through the first 5 and second 6 two-pole load, the first 7 and second 8 output transistors, the bases of which are combined , the collectors are connected to the corresponding first 2 and second 3 current outputs of the input differential stage 1, and the emitters are connected to the second 9 bus of the power source, a buffer amplifier 10, the input of which is connected to the second 3 currents the output output of the input differential stage 1. The first 11 and second 12 additional transistors are introduced into the circuit, the emitters of which are connected to the first 13 additional current-stabilizing two-terminal devices, the bases are connected to the corresponding first 2 and second 3 current outputs of the input differential stage 1, the collector of the second 12 additional transistor is connected through the second 14 additional current-stabilizing two-terminal with the first 4 bus power source and connected to the input of an additional non-inverting amplifier 15, the output otorrhea connected to the bases of the first joint 7 and 8 of the second output transistors. In the particular case of figure 2, the input differential stage 1 is implemented on transistors 16, 17 and two-terminal 18. An additional non-inverting current amplifier can be performed on transistor 19 (figure 3) or zener diode 20 (figure 4).

Consider the operation of the proposed device of figure 2.

In static mode, the collector currents (I _ki ) of the transistors 16, 17 are set by a two-terminal _device 18:

where I ₀ = I _18/2 .

Static currents equal to 2I ₀ flow through the two-terminal loads 5 and 6 with the introduction of a general negative feedback.

Determine the voltage gain of the remote control circuit of Fig.2.

If the input is Bx. ⁽⁺⁾ 1 voltage u _in is applied, then this causes an increase in the collector current of transistor 16 and a decrease in the collector current of transistor 17. As a result, the voltage at current output 3 increases (u ₃ > 0). Moreover, due to the negative feedback through an additional non-inverting amplifier 15, it ensures the equality u ₃ ≈u ₂ , where u ₂ is the voltage increment at the first 2 current output.

The change in u ₂ leads to a change in current i ₂ through the equivalent resistance r ₂ in the circuit of the first 2 current output of the input differential stage 1:

where r ₂ = R ₅ || R _{outx. 2} || R _{outx. 7} ,

R ₅ is the resistance of the bipolar load 5;

R _oy.2 - output resistance of the input differential stage 1 at the first 2 current output;

R _o.7 - the output impedance of the transistor 7.

Moreover

where U _Earley - voltage Earley transistor 7;

r ₁₆ = r _e17 = 2φ _t / I ₁₈ - resistance of the emitter junctions of transistors 16 and 17;

µ ₁₂ is the internal feedback coefficient of the transistor 16.

The increment of current i ₂ due to negative feedback through an additional non-inverting amplifier 15 enters the collector of transistor 7 and then to its output - to the circuit of the second 3 current output of the input differential stage 1. It should be noted that in the claimed circuit due to its structural features equality of alternating stresses is provided

Therefore, in node 3 there is a mutual compensation of the current through r _{3 by the} current through r ₂ = r ₃ .

If in a particular case we choose r ₂ = r ₃ , then the equivalent resistance in node 3 (R _3.eq ), affecting K _у , will practically determine the load resistance of the remote control brought to node 3.

Therefore, the voltage gain of the proposed circuit of Fig.2 weakly depends on the resistances of the two-terminal 5 and 6, which can be quite low resistance.

Thus, in the circuit of FIG. 2, the influence of the resistance of the two-terminal load 5 and 6 on the gain K _y on the voltage of the remote control decreases by one or two orders of magnitude.

As a result, the proposed circuitry solution improves by more than an order of K _у.max (by 29 dB), and this is achieved by using low-resistance resistors as bipolar 5 and 6 (R ₅ = R ₆ = 600 Ohms), as well as with a low-voltage supply voltage (± 2 V).

Presented in Figures 7, 8, 9, 10, the graphs confirm these theoretical conclusions.

Thus, the proposed device, when implemented within the framework of the SGB25VD process technology, has significant advantages in terms of voltage gain K _у in comparison with the known remote control.

Information sources

1. French patent No. 2409640.

2. US Patent No. 5,886.577.

3. England patent GB 2008883.

4. US Patent Application US 2009/108882, fig. 3.

5. Japanese Patent JP 54079553.

6. Patent WO 9621271.

7. US patent No. 4276485.

8. Patent application US 2006/0181347, fig.2.

9. Patent application WO 2009 / 042474A2, fig. 5.

10. US patent No. 6.396.346.

11. US patent No. 4.001.608, fig. 1.

12. Budyakov A. Design of Fully Differential OpAmps for GHz Range Applications [Text] / Budyakov A., Schmalz K., Prokopenko N., Scheytt C., Ostrovskyy P. // Problems of modern analog microcircuitry: collection. materials of the VI International scientific and practical seminar. In 3 hours, part 1. Functional nodes of analog integrated circuits and complex functional blocks / ed. N.N. Prokopenko. - Mines: Publishing house of SRUES, 2007 - S.106-110.

13. S.P. Voinigescu, et al. Design Methodology and Applications of SiGe BiCMOS Cascode Opamps with up to 37-GHz Unity Gain Bandwidth, IEEE CSICS, Techn. Digest, pp. 283-286, Nov. 2005, FIG. 2.

14. S.P. Voinigescu, et al. SiGe BiCMOS for Analog, High-Speed Digital and Millimetre-Wave Applications Beyond 50 GHz, IEEE BCTM, p. 1-8, Oct. 2006.

15. US patent No. 4.274.394, figure 2.

16. US Patent No. 3,619,797.

17. US patent No. 3.622.902.

18. US patent No. 3.440.554.

19. A.S. USSR №299013.

20. Patent of England No. 1.175.329, Н3Т.

21. US patent No. 3.304.512.

22. US patent No. 4.371.93.

23. A.S. USSR No. 421105.

24. A.S. USSR No. 764100.

25. A.S. USSR No. 669471.

Claims (1)

A differential amplifier with an increased gain, comprising an input differential stage with first and second current outputs connected to the first bus of the power source through the first and second two-terminal loads, the first and second output transistors, the bases of which are combined, the collectors are connected to the corresponding first and second current outputs input differential stage, and emitters are connected to the second bus of the power source, a buffer amplifier, the input of which is connected to the second current output input o differential cascade, characterized in that the first and second additional transistors are introduced into the circuit, the emitters of which are connected to the first additional current-stabilizing bipolar, the bases are connected to the corresponding first and second current outputs of the input differential cascade, the collector of the second additional transistor is connected via a second additional current-stabilizing bipolar to the first bus of the power source and is connected to the input of an additional non-inverting amplifier, the output of which is bases of the connections with the combined first and second output transistors.

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