SU764099A1 - Differential amplifier - Google Patents

Description

  .

The invention relates to radio engineering and can be used in operational amplifiers, comparators and other devices for automation, telemechanics and computer technology .;

The known differential amplifier contains the first and second series-connected differential cascades and three current generators, two of which are included in the collector and emitter circuits of the transistors of the first differential stage, respectively, and the third is connected via a resistor to the emitter circuit of the transistors of the second differential cascade, as well as a feedback transistor , the base of which is connected to the emitter circuit of transistors of the first differential cascade 1.

However, the known differential amplifier has a narrow dynamic range.

The purpose of the invention is to expand the dynamic range of the amplifier.

To do this in a differential amplification body; containing the first and second differential stages and three current generators, two of which are included respectively

In the collector and emitter circuit of the transistors of the first differential cascade, and the third through a resistor connected to the emitter circuit of the transistors of the second differential cascade, as well as the feedback transistor, the base of which is connected to the emitter circuit of the transistors of the first differential cascade, the collector of the feedback transistor is connected to control input of one of the current differential generators of the first cascade, and the emitter to the connection point of the resistor and the third 10 of its current generator of the second differential circuit about cascade. /

The drawing shows a circuit diagram of the proposed amplifier.

15

The amplifier contains the first differential cascade on transistors I, 2, the second differential cascade on transistors 3, 4. The emitter circuits of input transistors 1, 2 and output transistors 3, 4 include current generators 5, 6.

20 Collector resistors 7, 8 and 9, 10 of the first and second differential stages are connected to a current generator 1I, performed on transistor 12. Transistor emitter

-12 is connected to the power supply directly, and the base is via a resistor 13. The common emitter point of transistors 1, 2 is connected to the base of the control transistor 14 feedback, and the combined emitters of transistors 3, 4 are connected to the emitter of transistor 14 and current generator 6 through resistor 15 and diode 16.

The control transistor 14 collector is connected to the base of the transistor 12 through an auxiliary transistor 17, the base of which is connected to the output of the generator 11 - the collector of the transistor 12. The emitter of the transistor 14 is connected to the output of the generator / I via a capacitor 18.

The input signals are applied to the bases of transistors 1, 2, and a load is connected between the collectors of transistors 3, 4 and a differential amplifier.

The amplifier works as follows.

The collector-base voltage of the transistors I, 2 is automatically determined by the stabilizing effect of deep feedback on the common mode signal and the voltage drop across the resistor 15. The current through the resistor 15 is determined by the difference between the output current of the generator 6 and the emitter current of the transistor 14, which is not varies over a wide range of common mode changes and can be chosen much less than the output current of generator 6. Thus, the operating point of the input transistors is set by the appropriate choice of the nominal resistor 15.

With a positive input offset, the voltage at the base of the transistor 14 becomes more positive with respect to the emitter. This causes an increase in the collector current of the transistor 14 and a decrease in the collector voltage | -emitter of transistor 12. The emitter potential of transistor 14 also receives a voltage increase equal to the increment of the common-mode voltage at the input of the differential amplifier, and the further increase in the collector current of transistor 14 stops. Having established the voltage difference, the emitter-base of transistor 14 is slightly different from its original value due to the fact that the emitter current of transistor 14 is kept constant due to the stabilizing effect of deep negative feedback on the common-mode signal. Thus, the voltage drop across the resistor 15 and, therefore, the collector voltage of the transistors 1, 2 remain constant in a wide range of input common mode signal, which causes high values of the common mode suppression factor. .

With negative polarity of the input common mode voltage, the differential amplifier operates in a similar way.

except that the increment of the common mode signal causes not a decrease, but an increase in the collector voltage: - the transistor 12.

The emitter of the transistor 12 generator 11

current can be connected to the power supply directly. This clears the range of allowable common mode voltages at the input of the differential amplifier. A further increase in common mode rejection ratio is associated

0 with an increase in the output resistance of the generator 5 current in the emitter circuit of transistors 1, 2.

To eliminate the bypass action

the input resistance of the transistor 14

 the collector of transistor 14 is connected to the emitter of the auxiliary transistor 17. Such a connection provides an increase in the total resistance in the emitter circuit of transistors 1.2.

Voltage between emitter and base

Q transistor 12 is in the range of 0.5-0.7 V. This allows you to choose the emitter current of transistor 14 in the range from one to ten microamperes, even if there are restrictions on the values of resistors. Thus, low levels are achieved.

S of the base current of the transistor 14 (/ / e / P + Bc ') 10-t-100 nA, where fitn, is the static gain factor of the transistor 14 in the microray). Low base current levels of transistor 14 allow for stable operation of transistors 1 and 2 at emitter currents / d - 1 10 µA.

To reduce the temperature error of the tracking circuit, Due to the temperature dependence of the emitter base voltage of transistor 14, a diode 16 is shifted in the forward direction in series with the resistor 15 in the emitter circuit of the output transistors 3, 4. Turning on the diode 16 significantly reduces the temperature instability of the collector-base voltage of the input transistors I and 2, which also

 reduces the temperature instability of the bias zero voltage of a differential amplifier. Thus, the proposed amplifier has an increased temperature stability of the coordinates of the working

, points of input transistors.

A significant increase in the rate of rise of the output voltage can be achieved by changing the current of the generator 5 according to a certain law.

0 Increasing the generator current 5 lead to a decrease in the collector-base voltage of the input transistors 1, 2, which causes an in-phase voltage shift at the output of the generator 6, an increase in the collector current of transistor 14 and a decrease in the collector-emitter voltage of transistor 12. As a result, the collector -emitter of transistors 1 and 2 is almost unchanged. This ensures reliable operation.

Claims (1)

Claim A differential amplifier comprising first and second series included ₂₀