RU2402152C1 - Cascode differential amplifier with low voltage of zero shift - Google Patents

Abstract

FIELD: radio engineering. ^ SUBSTANCE: cascode differential amplifier comprises input differential cascade (DC) (1), with the first (2) and second (3) current outputs, the first (4) and second (5) output transistors (T) with combined bases, auxiliary source of voltage (6), the first current mirror (CM) (7), input of which is connected to collector T (4), output is connected to collector T (5) and input (8) of buffer amplifier (9), comprising input T (10), besides type of conductivity of input T (10) of buffer amplifier (9) is identical to type of conductivity of T (4) and T (5), emitter T (4) is connected to the first (2) output of DC (1), and emitter T (5) is connected to the second (3) current output of DC (1). Circuit includes the second CM (16), input of which is connected to bases T (4) and T (5), output is connected to emitter T (5), and common unit is connected to auxiliary source of supply voltage (6). ^ EFFECT: reduced absolute value of shift voltage and its temperature drift. ^ 8 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, in comparators and precision operational amplifiers (op amps) with small values of the emf of zero bias).

In modern electronic equipment, differential amplifiers (DU) with significantly different parameters are used. A special place is occupied by cascode remote controls with the simplest two-stage architecture, containing a small number of elements and characterized by an increased frequency range [1-12]. On their basis, for example, various classes of selective circuits are performed, where the number of low-power amplifiers can be measured in tens of units. The present invention relates to this type of remote control.

As a prototype, the authors chose a cascode differential amplifier included in the structure of the voltage follower (stabilizer) according to French patent 2.227.574 (diagram fig.1 using the following combinations of functional units: fig.3c and fig.4a). The same technical solution is patented in three more countries NL, DE, JP [12].

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.

This goal is achieved in that in the differential amplifier of figure 1, containing the input differential stage 1 with the first 2 and second 3 current outputs, the first 4 and second 5 output transistors with integrated bases, an auxiliary voltage source 6, the first current mirror 7, input which is connected to the collector of the first 4 output transistor, the output is connected to the collector of the second 5 output transistor and input 8 of the buffer amplifier 9 containing the input 10 transistor, and the type of conductivity of the input 10 transistor buffer The black amplifier 9 is identical to the conductivity type of the first 4 and second 5 output transistors, the emitter of the first 4 output transistor is connected to the first 2 current output of the input differential stage, and the emitter of the second 5 output transistor is connected to the second 3 current output of the input differential stage 1, new elements and connection - the second current mirror 16 is introduced into the circuit, the input of which is connected to the bases of the first 4 and second 5 output transistors, the output is connected to the emitter of the second 5 output transistor, and the common node - connected to an auxiliary voltage supply 6.

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.

Figures 3 and 4 show particular cases of execution of the current mirror 11.

Figure 5 shows a diagram of the inventive device for the case when it uses the so-called "bent" cascode (elements 4, 5, 7, 10, 12).

In the circuit of FIG. 6 corresponding to FIG. 2, an additional thermoradiation compensation transistor 26 is introduced.

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

In Fig.8 shows the temperature dependence of the bias voltage zero of the schemes of Fig.7.

The cascode differential amplifier of FIG. 2 comprises an input differential stage 1 with first 2 and second 3 current outputs, first 4 and second 5 output transistors with integrated bases, an auxiliary voltage supply 6, a first current mirror 7, the input of which is connected to the collector of the first 4 output transistor, output - connected to the collector of the second 5 output transistor and input 8 of the buffer amplifier 9 containing the input 10 transistor, and the conductivity type of the input 10 of the transistor of the buffer amplifier 9 is identical to the type the conductivity of the first 4 and second 5 output transistors, the emitter of the first 4 output transistor is connected to the first 2 current output of the input differential stage, and the emitter of the second 5 output transistor is connected to the second 3 current output of the input differential stage 1. The second current mirror 16 is input into the circuit, input which is connected with the bases of the first 4 and second 5 output transistors, the output is connected to the emitter of the second 5 output transistor, and the common node is connected to an auxiliary source of supply voltage 6.

In a particular case, the buffer amplifier 9 in the circuit of figure 2 contains a current-stabilizing two-terminal 12, and the input parallel-balanced cascade 1 is implemented on transistors 13, 14 and two-terminal 15.

Current mirrors 11 in figure 3 and 4 are made on the elements 16, 17, 18 and 19.

In the circuit of FIG. 5, the input parallel-balanced stage 1 is implemented on transistors 20 and 21, as well as two-terminal devices 22, 23 and 24, and a potential matching circuit 25 is introduced into the buffer amplifier 9.

In the circuit of FIG. 6, a thermoradiation compensation transistor 26 is introduced, having (like the transistor 17 of the current mirror 11) a pn junction to the substrate 27 that is identical to the pn junction 28 of the transistor 17.

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

If the current 15 is equal to the two-terminal 2I _0, the output currents of 2 and 3, the input (I .7 _Rin) and output (I _Vyh.7) currents subcircuit 7:

where I _bp = I _e.i / β _i is the base current of npn transistors 4, 5, 13, 14, 10 with an emitter current I _e.i = I ₀ ;

β _i is the current gain of the base npn of the transistor.

As a result, the current difference in the node "A" when it is shorted to the equipotential common bus

where I = 2I _{BU BR} - npn transistor 10, the base current of the buffer amplifier 9. Substituting (3) ÷ (6) in (7), we find that the difference current, which determines U _cm,

As a result, when I _p = 0, zero offset DN1 of FIG. 2 is not required by U _cm , the supply of which to its inputs Bx. ⁽⁺⁾ 1, In. ^(-) 2 compensates for the differential current I _p in the node "A".

Thus, in the inventive device, the systematic component U _cm decreases due to the final value of β transistors and its radiation (or temperature) dependence. 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 differential voltage U _{in the} remote control into the output current of the node “A”:

where r _e14 = r _e13 - resistance of the input emitter transitions

transistors 14 and 13 of the differential stage 1.

Therefore, for the circuit of FIG. 2

where φ _t = 26 mV is the temperature potential.

In the remote control prototype of FIG. 1, I _p ≠ 0, therefore, here the systematic component U _{cm. 1} is an order of magnitude larger (U _CM.1 = -1.17 mV) than in the claimed circuit (U _CM.1 = 43 μV, (Fig. 8)).

Computer simulation of the schemes of figure 3 confirms (figure 4) these theoretical conclusions.

If it is necessary to ensure the symmetry of the amplitudes of the positive and negative half-waves of the output voltage of the remote control of Fig. 7, then a second potential bias circuit V4 should be introduced.

To minimize U _{see 1} at elevated temperatures (t °> 80 ° C) in the circuit of Fig.6 provides a transistor 26, which is in the closed state. However, the current through its p-n junction on a substrate 27, which increases substantially at higher temperatures (at or radiation effects) compensates a corresponding current on the substrate through the p-n junction 28 of transistor 17. This significantly reduces the derivative dU _cm / dT at t ° > 80 ° C.

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.

Information sources

1. US patent No. 6.114.234.

2. US Patent No. 5.091.701, fig. 1.

3. US Patent No. 5.140.280.

4. US Patent No. 5,786.729.

5. US patent No. 6.448.853.

6. US Patent No. 4,390.850.

7. US Patent No. 5,327,100 fig. 2.

8. US patent No. 6.4383.382 fig.2, fig.1.

9. US patent No. 5.374.897.

10. US Patent No. 6.529.076.

11. US Patent No. 5,627,495 fig. 2.

12. French patent No. 2.227.574 fig. 1, fig. 3c, fig. 4a.

Claims (1)

A cascode differential amplifier with a low zero bias voltage, comprising an input differential stage (1) with first (2) and second (3) current outputs, first (4) and second (5) output transistors with integrated bases, an auxiliary power supply voltage (6 ), the first current mirror (7), the input of which is connected to the collector of the first (4) output transistor, the output is connected to the collector of the second (5) output transistor and the input (8) of the buffer amplifier (9) containing the input (10) transistor, input conductivity type (10) the buffer amplifier resistor (9) is identical to the conductivity type of the first (4) and second (5) output transistors, the emitter of the first (4) output transistor is connected to the first (2) current output of the input differential stage, and the emitter of the second (5) output transistor is connected to the second (3) current output of the input differential stage (1), characterized in that a second current mirror (16) is introduced into the circuit, the input of which is connected to the bases of the first (4) and second (5) output transistors, the output is connected to the emitter of the second ( 5) the output transistor, and commonly the first node is connected with an auxiliary source of supply voltage (6).

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