RU2449466C1 - Precision operational amplifier - Google Patents

Abstract

FIELD: radio engineering.

SUBSTANCE: precision operational amplifier comprises an input differential cascade, the first and second output transistors, an additional transistor, a current-stabilising dipole, an additional source of reference current, a forward-based p-n transition, a buffer amplifier.

EFFECT: reduced absolute value of zero shift voltage and its temperature and radiation drift.

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Description

The invention relates to the field of radio engineering and communications and can be used as a device for amplifying analog signals in the structure of analog microcircuits for various functional purposes.

In modern microelectronics, the architecture of operational amplifiers (op amps) based on cascode current mirrors (TK) with their asymmetric inclusion is widely used [1-5]. Such op amps have the following advantages:

- high voltage gain, due to the increased output resistance of cascode TK;

- large range of output voltage variation (rail-to-rail option);

- Good frequency response due to cascode current mirror.

These advantages are realized in a number of serial op-amps (154UD1, NA2700, 154UD4, etc.). However, the opamps of this subclass have a relatively large level of zero bias voltage (U _cm ) and its temperature drift.

It should also be noted that op-amps with other options for constructing current mirrors and their asymmetric inclusion are quite popular in analog microcircuitry (WO 2002/047257, US 6.657.465, US 6.844.781, US 7.782.139 fig.5, US 4.366.442, US 4.433.302, US 4.262,261, US 2006/0012432 fig. 6, US 2006/0006910 fig. 11, US 2008/0032656 fig. 6, etc.).

The closest prototype (Fig. 1) of the claimed device is OU 154UD4, presented in the monograph by V.V. Matavkin “High-speed operational amplifiers”. - M., Radio and communications, 1989. - S. 100. - Fig. 6.9. The same architecture is presented in [5], in which, however, the output buffer amplifier is indicated by the equivalent load.

A significant disadvantage of the known op-amp of FIG. 1 is that it has an increased value of the systematic component of the zero bias voltage (U _cm ) associated with the asymmetry of its architecture.

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

The problem is solved in that in the precision operational amplifier of figure 1, containing the input differential stage 1 with the first 2 and second 3 current outputs, the first power bus 4, the first 5 output transistor, the emitter of which is connected to the first 4 bus of the power source, and the base connected to the first 4 bus of the power supply through a forward biased pn junction 6, the second 7 output transistor, the emitter of which is connected to the collector of the first 5 output transistor, and the collector is connected through the current-stabilizing two-terminal 8 to the second 9 bus and the power source and the input of the buffer amplifier 10, and the second 9 bus of the power source is connected to the emitter circuit of the input differential stage 1, new elements and connections are provided - an additional transistor 11 is introduced into the circuit, the base of which is connected to the base of the first 5 output transistor, the collector is connected to the first 4 by a power supply bus, and the emitter is connected to the output 12 of an additional reference current source 13.

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 and claim 2 of the claims.

The drawing of figure 3 shows a diagram corresponding to claim 3 of the claims.

The drawing of Fig. 4 shows a diagram of an op-amp prototype, and Fig. 5 is a diagram of a proposed opamp of Fig. 2 in a PSpice environment on models of integrated transistors ABMK_1_3 (Transistors: npn GC1E, pnp JFpnp, abmk1.3, OJSC "MNIPI") .

The drawing of Fig.6 shows the temperature dependence of the output voltage U _cm compared opamp 4, Fig.5. The drawing of Fig.7 shows the logarithmic amplitude-frequency characteristics of the gain in voltage of the compared op amp of Fig.4 and Fig.5,

The drawing of Fig. 8 shows the proposed circuit of the op-amp of Fig. 3 in the PSpice environment on the models of integrated transistors ABMK_1_3 (Transistors: npn GC1E, pnp JFpnp, abmk1.3, OJSC "MNIPI").

The drawing of Fig.9 shows the temperature dependence of the output voltage U _cm compared opamp of Fig.4 and Fig.8.

The precision operational amplifier of FIG. 2 comprises an input differential stage 1 with first 2 and second 3 current outputs, a first power bus 4, a first 5 output transistor, the emitter of which is connected to the first 4 bus of the power source, and the base is connected to the first 4 bus of the power source through forward biased pn junction 6, second 7 output transistor, the emitter of which is connected to the collector of the first 5 output transistor, and the collector is connected to the second 9 bus of the power source and the input of the buffer force through a current-stabilizing two-terminal 8 eating 10, and the second 9 bus of the power source is connected to the emitter circuit of the input differential stage 1. An additional transistor 11 is introduced into the circuit, the base of which is connected to the base of the first 5 output transistor, the collector is connected to the first 4 bus of the power source, and the emitter is connected to output 12 additional reference current source 13. In the particular case (figure 2), the input differential stage 1 is implemented on transistors 14, 15 and the current source 16.

In addition, in the drawing of FIG. 2, in accordance with claim 2, the first 2 current output of the input differential stage 1 is connected to the first 4 bus of the power source through an auxiliary pn junction 17.

In the drawing of figure 3, in accordance with claim 3 of the claims, the first 2 current output of the input differential stage 1 is used as an additional source of reference current 13.

Consider the factors that determine the systematic component of the bias voltage zero (U _cm ) in the circuit of figure 2, i.e. circuit-dependent op amps.

If the current of the two-terminal 16 is equal to 2I ₀ , the two-terminal 13 is x ₁ I ₀ , the two-terminal 18 is equal to I ₀ , then the currents of the emitters (I _ei ) and collectors (I _кi ) of the transistors of the circuit, as well as the currents of the pn junctions 6 (I ₆ ) and 17 (I ₁₇ ):

where I _bi = I _ei / β _i is the base current of npn (I _br ) or pnp (I _bn ) transistors with an emitter current I _ei = I ₀ ;

β _i is the current gain of the base of the i-th transistor;

x ₁ is the scaled current coefficient of the two-terminal 13.

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

where I _BU = x _p I _br -x _n I _bn ;

x _p , x _n are the scale factors of the oppositely directed components (I _br , I _bn ) of the input current I _{BU of the} buffer amplifier 10, for which it is advisable to use the classic complementary emitter repeaters (Fig. 5, Fig. 4).

Thus, as follows from (6), in the inventive device, when the condition x _n = 3, x _p = x ₁ -1 is satisfied, the systematic component U _cm decreases due to the finite value of β transistors and its radiation (or temperature) dependence (x _p ≈0). 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 (S) of the conversion of the input differential voltage of the op-amp (u _in ) to the output current of the node “A”:

where r _e14 = r _e15 - resistance of the emitter junctions of the input transistors 14 and 15 of the input differential stage 1.

Therefore, for the circuit of FIG. 2

where φ _t = 26 mV is the temperature potential.

In the op-amp prototype of figure 1, I _p ≠ 0, therefore, here the systematic component U _{cm is} obtained at least an order of magnitude more than in the claimed scheme.

The introduction of the pn junction 17 provides a further decrease in the temperature drift of U _cm due to the balancing of the static regime with respect to the collector-base voltage of transistors 14 and 15, which weakens the effect of internal feedback on U _cm .

Computer simulation of the circuits of Fig. 4, Fig. 5 confirms (Fig. 6) these theoretical conclusions. Despite the change in β transistors due to external influences, the proposed op-amp is more than 50 times lower in bias voltage than the op-amp. Similar properties are possessed by the diagram of FIG.

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 and can be used as IP modules of precision interfaces.

Literature

1. Patent RU 1160530.

2. Patent RU 2193273 figure 2.

3. Matavkin VV High-speed operational amplifiers. - M., Radio and communications, 1989. - S. 100. - Fig. 6.9.

4. Matavkin VV. High-speed operational amplifiers. - M., Radio and communications, 1989. - P.75. - Fig. 4.16.

5. Matavkin VV. High-speed operational amplifiers. - M., Radio and communications, 1989. - P.30. - Fig. 2.12a.

Claims (3)

1. A precision operational amplifier comprising an input differential stage (1) with first (2) and second (3) current outputs, a first power rail (4), a first (5) output transistor, the emitter of which is connected to the first (4) source bus power supply, and the base is connected to the first (4) bus of the power source through the forward biased pn junction (6), the second (7) output transistor, the emitter of which is connected to the collector of the first (5) output transistor, and the collector is connected through a current-stabilizing two-terminal device (8) to second (9) power supply bus and buffer input amplifier (10), and the second (9) bus of the power source is connected to the emitter circuit of the input differential stage (1), characterized in that an additional transistor (11) is introduced into the circuit, the base of which is connected to the base of the first (5) output transistor, the collector is connected to the first (4) bus of the power source, and the emitter is connected to the output (12) of an additional reference current source (13). 2. The precision operational amplifier according to claim 1, characterized in that the first (2) current output of the input differential stage (1) is connected to the first (4) bus of the power source through an auxiliary pn junction (17). 3. The precision operational amplifier according to claim 1, characterized in that the first (2) current output of the input differential stage (1) is used as an additional source of reference current (13).

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