RU2390914C1 - Cascode differential amplifier with low voltage of zero shift - Google Patents

Abstract

FIELD: radio engineering.

SUBSTANCE: invention may be used as device for amplification of analogue signals, in structure of analogue microchips of various functional purpose (for instance, operational amplifiers (OA) with low values of zero shift EMF). Cascode differential amplifier with low voltage of zero shift comprises input differential cascade (1) with the first (2) and second (3) collector outputs connected to emitters of according first (4) and second (5) output transistors, auxiliary source of voltage (6) connected to bases of the first (4) and second (5) output transistors, current mirror (7), input of which is connected to collector of the first (4) output transistor, and outlet - to collector of the second (5) output transistor and base of input transistor (8) of buffer amplifier, circuit of buffer amplifier (9) load connected to its output (10). Circuit comprises additional transistor (11), base of which is connected to the second (3) current output of input differential cascade (1), emitter is connected to collector of input transistor (8) of buffer amplifier, and collector is connected to output (10) of buffer amplifier.

EFFECT: reduced shift voltage.

3 cl, 5 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 for various functional purposes (for example, broadband operational amplifiers (op amps) with small values of zero emf bias voltage U _cm ).

In modern electronic equipment, differential amplifiers (DU) with significant different parameters are used. A special place is occupied by cascode architecture remote controls, which are among the most high-frequency ones. The alleged invention relates to this type of device [1-16].

Closest to the technical nature of the claimed remote control is the classical circuit of figure 1 (US patent No. 4.232.273), which has become the basis for constructing a large number of analog devices and interfaces.

A significant disadvantage of the known DE figure 1 is that it has an increased value of the bias voltage zero _CM U.

The main objective of the invention is to reduce U _CM .

This goal is achieved by the fact that in the cascode differential amplifier of figure 1, containing the input differential stage 1 with the first 2 and second 3 collector outputs associated with the emitters of the corresponding first 4 and second 5 output transistors, an auxiliary voltage source 6 connected to the bases of the first 4 and the second 5 output transistors, a current mirror 7, the input of which is connected to the collector of the first 4 output transistor, and the output to the collector of the second 5 output transistor and the base of the input transistor 8 buffer of the amplifier, the load circuit of the buffer amplifier 9, connected to its output 10, new elements and connections are provided - an additional transistor 11 is introduced into the circuit, the base of which is connected to the second 3 current output of the input differential stage 1, the emitter is connected to the collector of the input transistor 8 of the buffer amplifier , and the collector is connected to the output 10 of the buffer amplifier.

The amplifier circuit of the prototype is shown in the drawing of figure 1. The drawing of figure 2 presents a diagram of the inventive device in accordance with claim 1, claim 3 of the claims. The drawing of figure 3 shows the static currents in the circuit of the inventive device of figure 2. However, the type of conductivity used in the circuit of FIG. 3 is the opposite of the type of conductivity of the corresponding transistors in the circuit of FIG. 2.

The drawing of figure 4 shows the diagram of the remote control prototype in the computer simulation environment PSpice on the models of integrated transistors of the Federal State Unitary Enterprise NPP Pulsar and the results of calculating its zero bias voltage: U _cm = 576 μV.

The drawing of figure 5 shows a diagram of the inventive device in a computer simulation environment PSpice on models of integrated transistors of the Federal State Unitary Enterprise NPP Pulsar, as well as the results of determining the systematic component of its zero bias voltage: U _cm = -38.8 μV.

The cascode differential amplifier of FIG. 2 contains an input differential stage 1 with a first 2 and a second 3 collector outputs connected to emitters of the corresponding first 4 and second 5 output transistors, an auxiliary voltage source 6 connected to the bases of the first 4 and second 5 output transistors, a current mirror 7, the input of which is connected to the collector of the first 4 output transistor, and the output to the collector of the second 5 output transistor and the base of the input transistor 8 of the buffer amplifier, the load circuit of the buffer amplifier of Tell 9 connected to its output 10. The circuit introduced an additional transistor 11, whose base is connected to the second current output 3 of the differential input stage 1, whose emitter is connected with the input of the buffer amplifier transistor the collector 8 and whose collector is connected to the output 10 of the buffer amplifier.

In the drawings of FIG. 2 and FIG. 3, in accordance with claim 2, the current mirror 7 comprises a pn junction 12 and an output transistor 13, the base of the output transistor 13 being connected to the input of the current mirror 7 and the first output of the pn junction 12, the collector connected to the output of the current mirror 7, and the emitter is connected to the second terminal pn of junction 12.

In the drawing of figure 4, corresponding to claim 3 of the claims, the output 10 of the buffer amplifier is connected to the input of the output voltage follower 14.

Consider the operation of the circuit of figure 3 on direct current.

In connection with the final value of the current transfer coefficient of the base of transistors (β = 20 ÷ 50) for the circuit of Fig.3, the following Kirchhoff equations can be made:

where I _k4 , I _k5 , I _k8 , I _k13 - collector currents of transistors 4, 5, 8, 13;

I ₁₂ - current through pn junction 12;

I _e5 , I _e13 - emitter current of transistors 5 and 13;

2I ₀ is the total current of the common emitter circuit of the input differential stage.

The sum of the currents for the node "A"

or after conversion

Given the numerical values of β, the last equation can be represented as

.

.

Thus, with β ₈ ≈ β ₁₁ ≈ β ₁₃ and the same change in β transistors under the influence of radiation (or temperature) in node “A”, mutual compensation of error currents associated with the final values of the base currents is provided. As a result, this reduces U _cm , since the differential current I _p in the node “A” creates U _cm , which depends on the steepness of the conversion of the input voltage u _{in the} remote control of FIG. 3 into the output current of the node “A”

,

,

where r _e1 = r _e2 is the resistance of the emitter junctions of the input transistors of the differential stage 1. Therefore, for the circuits of figure 1 - figure 3

U _cm = I _p (r _e1 + r _e2 ).

In the remote control prototype I _R ≠ 0, therefore, here the systematic component U _{CM is} obtained an order of magnitude more (Fig. 4) than in the claimed scheme (Fig. 5).

Thus, the proposed technical solution has a significant advantage in comparison with the prototype.

Information sources

1. US patent No. 3.660.773.

2. French Patent No. 1,484.340.

3. The Federal Republic of Germany patent No. 1.214.775.

4. Patent of England No. 1520085.

5. US Patent No. 3,482.177.

6. Patent of England No. 1212342.

7. German patent No. 1537590.

8. French patent No. 1548008.

9. Patent application of Germany No. 2418455.

10. French patent No. 2227574.

11. Av. testimonial. USSR No. 970638.

12. Swedish patent No. 359989.

13. Patent of England No. 1500993.

14. Av. testimonial. USSR No. 276170.

15. Patent of England No. 1334759.

16. Japanese Patent No. 53-35352.

Claims (3)

1. A cascode differential amplifier with a low zero bias voltage, comprising an input differential stage (1) with first (2) and second (3) collector outputs connected to emitters of the corresponding first (4) and second (5) output transistors, an auxiliary voltage source (6) connected to the bases of the first (4) and second (5) output transistors, a current mirror (7), the input of which is connected to the collector of the first (4) output transistor, and the output to the collector of the second (5) output transistor input transistor (8) buffer amplifier, the load circuit of the buffer amplifier (9) connected to its output (10), characterized in that an additional transistor (11) is introduced into the circuit, the base of which is connected to the second (3) current output of the input differential stage (1), emitter connected to the collector of the input transistor (8) of the buffer amplifier, and the collector is connected to the output (10) of the buffer amplifier. 2. The device according to claim 1, characterized in that the current mirror (7) contains a pn junction (12) and an output transistor (13), the base of the output transistor (13) connected to the input of the current mirror (7) and the first output pn of the junction (12), the collector is connected to the output of the current mirror (7), and the emitter is connected to the second terminal pn of the junction (12). 3. The device according to claim 1, characterized in that the output (10) of the buffer amplifier is connected to the input of the output voltage follower (14).

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