RU2411641C1 - Differential operational amplifier with low voltage of zero shift - Google Patents

Abstract

FIELD: radio engineering.

SUBSTANCE: invention may be used as device for amplification of analog signals, in structure of analog microchips of various functional purpose (for instance, in comparators and precision operational amplifiers (OA) with low values of zero shift electromotive force). Differential operational amplifier comprises the first (1) and second (2) input transistors, between emitters of which a resistor (3) of local negative feedback is connected, the first (4) and second (5) current-stabilising dipoles (CD), current mirror (6), input of which is connected to collector of the first T (1), and output is connected to collector of the second T (2) and base of input T (7) of output emitter repeater (8). Circuit includes the first (9) and second (10) additional T, emitters of which are connected to according first CD (4) and second CD (5), collector of the first T (9) is connected to emitter of the first T (1), base of the first T (9) is connected to circuit of shift potentials (11), collector of the second T (10) is connected to emitter of the second T (2), and its base is connected to emitter of the first T (9).

EFFECT: reduced absolute value of U_cm and its temperature drift.

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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, in comparators and precision operational amplifiers (op amps) with low values of the zero-offset EMF).

In modern electronic equipment, differential amplifiers (DU) with significant different parameters are used.

A special place is occupied by differential amplifiers (DU) with local negative feedback, which is provided by a resistor connected between the emitters of the input transistors of the DU. Such remote controls are used in high-speed operational amplifiers and are characterized by an extended range of linear operation. The present invention relates to this type of remote control.

The closest in essence to the claimed technical solution is the classical scheme DU of FIG. 1, presented in US patent No. 5365191, which is also present in a large number of other patents, for example [1-13], having controllable current mirrors as a load circuit of input transistors [ 1-6] or uncontrolled current-stabilizing bipolar [7-13].

A significant drawback of the known DE of FIG. 1 is that it has an increased value of the systematic component of the zero bias voltage (U _cm ), which depends on the properties of its architecture.

The main objective of the invention is to reduce the absolute value of U _cm and its temperature drift.

The problem is achieved in that in the differential amplifier of Fig. 1, containing the first 1 and second 2 input transistors, between the emitters of which a resistor 3 of local negative feedback is connected, the first 4 and second 5 are current-stabilizing two-terminal devices, a current mirror 6, the input of which is connected to the collector the first 1 input transistor, and the output is connected to the collector of the second 2 input transistor and the base of the input transistor 7 of the output emitter follower 8, new elements and connections are provided - the first 9 and the second 10 additional transistors, the emitters of which are connected to the corresponding first 4 and second 5 current-stabilizing two-pole, the collector of the first 9 additional transistor is connected to the emitter of the first 1 input transistor, the base of the first 9 additional transistor is connected to the potential bias circuit 11, the collector of the second additional transistor 10 is connected to the emitter of the second 2 input transistor, and its base is connected to the emitter of the first 9 additional transistor.

The amplifier circuit of the prototype is shown in figure 1. Figure 2 presents a diagram of the inventive device in accordance with the claims.

Figure 3 shows the scheme of the differential prototype amplifier (left side) and the claimed remote control (right side) in the computer simulation environment PSpice on the models of integrated transistors of FSUE NPP Pulsar.

Figure 4 shows the temperature dependence of the zero bias voltage of the compared circuits of figure 3 when using transistors with a typical base current gain β = 50, and in the drawing of figure 5 with small β = 20.

The differential amplifier of Fig. 2 contains a first 1 and a second 2 input transistors, between the emitters of which a local negative feedback resistor 3 is included, the first 4 and second 5 current-stabilizing two-terminal devices, a current mirror 6, the input of which is connected to the collector of the first 1 input transistor, and the output is connected to the collector of the second 2 input transistor and the base of the input transistor 7 of the output emitter follower 8. The first 9 and second 10 additional transistors are introduced into the circuit, the emitters of which are connected to the corresponding in the first 4 and second 5 current-stabilizing two-pole, the collector of the first 9 additional transistor is connected to the emitter of the first 1 input transistor, the base of the first 9 additional transistor is connected to the potential bias circuit 11, the collector of the second 10 additional transistor is connected to the emitter of the second 2 input transistor, and its base is connected with the emitter of the first 9 additional transistor.

Consider the factors that determine the systematic component of the bias voltage of zero U _cm in the circuit of figure 2, i.e. depending on the circuitry of the remote control.

If the currents of the two-terminal circuits 4 and 5 are equal to the value I ₀ , then the collector currents of the transistors 9, 10, 1 and 2:

where I _bp = I _e.i / β _i is the base current of the transistors with an emitter current I _e.i = I ₀ ;

β _i is the current gain of the base of transistors.

Input (I _{input 6} ) and output (I output ₆ ) currents of the current mirror 6

where K _i - current transfer coefficient of the subcircuit 6 (K _i = 1).

As a result, the current difference in node “A” when it is short-circuited to an equipotential common bus

where I _BU - base current n-p-n transistor 7 emitter follower 8.

To obtain the zero value of the differential current I _p (6) it is necessary that the condition

Thus, in the inventive device, when condition (7) is satisfied, the systematic component U _cm decreases due to the finite value of β transistors and its radiation (or temperature) dependence. As a result, this reduces U _cm , since the difference current I _p in the node “A” creates U _cm , depending on the steepness S of the conversion of the input differential voltage u _{in the} remote control into the output current of the node “A”:

where r _e1 = r _e2 resistance of the emitter junctions of the input transistors 1 and 2 of the differential stage 1,

R ₃ - resistance of a two-terminal 3.

Therefore, for the circuit of FIG. 2

where φ _t = 26 mV is the temperature potential.

In the remote control prototype I _p = I _BU = I _bp ≠ 0, therefore, here the systematic component U _{cm is} obtained more than three orders of magnitude more (U _cm = -2.5 mV) than in the claimed scheme (U _cm = - 1.2 μV).

Computer simulation of the schemes of figure 3 confirms (figure 4, figure 5) these theoretical conclusions. Despite a significant decrease in β transistors due to radiation exposure, the proposed remote control has a lower bias voltage than the remote prototype (figure 5).

Thus, the claimed device has significant advantages in comparison with the prototype in terms of the value of the static error of amplification of DC signals.

BIBLIOGRAPHIC LIST

1. US patent No. 4636743, fig. 1.

2. U.S. Patent No. 5,828,242, fig. 5.

3. US Patent No. 5365191, fig. 9.

4. US patent No. 4636744.

5. US Patent No. 6,281,752, fig. 5a.

6. US patent No. 4783637.

7. US Patent No. 5734294.

8. US Patent Application 2006/0066362.

9. US patent No. 5684419.

10. US Patent No. 4757274, fig. 1.

11. US patent No. 4721920.

12. US patent No. 5184088.

13. US patent No. 4575687.

Claims (1)

A differential operational amplifier with a low zero bias voltage, containing the first (1) and second (2) input transistors, between the emitters of which a local negative feedback resistor (3) is connected, the first (4) and second (5) current-stabilizing two-pole, current mirror ( 6), the input of which is connected to the collector of the first (1) input transistor, and the output is connected to the collector of the second (2) input transistor and the base of the input transistor (7) of the output emitter follower (8), characterized in that the first (9 ) and second th (10) additional transistors, the emitters of which are connected to the corresponding first (4) and second (5) current-stabilizing two-terminal, the collector of the first (9) additional transistor is connected to the emitter of the first (1) input transistor, the base of the first (9) additional transistor is connected to potential bias circuit (11), the collector of the second (10) additional transistor is connected to the emitter of the second (2) input transistor, and its base is connected to the emitter of the first (9) additional transistor.

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