SU1550598A1 - Differential amplifier - Google Patents

Abstract

The invention relates to radio engineering and can be used as an input stage for high-speed operating instruments. The purpose of the invention is to increase the accuracy in the large signal mode. The amplifier contains transistors 1, 2, the emitters of which are combined, the bases are the y inputs, and the collectors are its outputs, a push-pull controlled current source 5, as well as the input transistors 3, 4, resistor 6, and a bias diode 7. At the same time the bases and collectors of transistors 1 and 3, 2 and 4 are pairwise combined. Transistors 1 and 2 actually operate at a constant bias current and affect the small signal mode, and transistors 3 and 4 are only effective in the large signal mode. The transistors 1, 2 determine the accuracy of the l, and the transistors 3, 4 - its speed. The gain in accuracy in the transmission of pulse signals is due to a significant decrease in the temperature difference between the transistors 1, 2. 1 sludge.

Description

SD JV

about ate with

00

The invention relates to radio engineering and can be used as an input stage for high-performance operational amplifiers.

The purpose of the invention is to increase the accuracy of a large signal.

The drawing shows a circuit diagram of the proposed differential amplifier.

The proposed differential amplifier contains the first, second, third, and fourth transistors 1–49 push-pull controlled current source 5, resistor 6, and a 7 j offset diode. The proposed differential amplifier operates as follows.

The output current of a push-pull controlled current source 5 in the quiescent mode and the resistance of the resistor 6 is chosen so that the voltage drop on this resistor is 50-100 mV less than the dip on the forward biased diode 7. In this case in the small signal mode, the bias current of the third and fourth transistors 3 and 4 is negligible compared with the bias current of the first and second transistors 1 and 2 and the effect of these transistors on the device in the small signal mode can be neglected. In this case, the operation of the device in the mode of a small signal does not differ from the operation of the device of the prototype.

I

When operating in the large signal mode, the output current of a push-pull controlled current source 5 varies over a wide range. Let us assume, for example, that when a high-speed impulse differential is transmitted, this current increases by an order of magnitude compared with the value in the low-signal mode. Since the dependence of the voltage on a pn junction on current is logarithmic, an increase in the output current of a push-pull controlled current source 5 leads to only a slight increase in voltage on the base-emitter transitions of the third and fourth transistors 3 and 4 and on a forward-biased diode 7 (approximately 200 mV). If, in the quiescent mode, the total voltage drop across these p-n junctions was, for example, 1.2 V, then the bias current of the first and second transistors 1 and 2 during transmission

.

0 5 Q

five

0

five

0

five

Claims (1)

impulse drops change by 30% 5 while the bias current of the third and fourth transistors 3 and 4 increases by approximately 20-30 times. Therefore, the functions of these: transistors are separated - the first and second transistors 1 and 2 actually operate at constant current bias and affect only the small signal mode, and the third and fourth transistors 3 and 4 are effective only in the large signal mode. The first and second transistors 1 and 2 determine the accuracy of the device, and the third and fourth transistors 3 and 4 - its performance. The current displacement mode of the first and second transistors 1 and 2 in the proposed device, compared with the prototype, during the transmission of pulsed drops varies to a much lesser extent than the significantly smaller temperature difference between the first and second transistors 1 and 2, which determine the accuracy of the device. Since the entire displacement gain closes through the third and fourth transistors 3 and 4, the temperature of these transistors may change significantly in the switching process, but this does not affect the accuracy of the device. Thus, the proposed device has high accuracy. Invention Formula The differential amplifier containing the first and second transistors of the emitters of which are combined, the bases are the inputs of the differential amplifier, and the collectors are its outputs, as well as a push-pull controlled current source whose common bus is connected to the corresponding power supply bus. In order to increase accuracy in the large signal mode, the third and fourth transistors of the same type are introduced, the emitters of which are combined, and the bases and collectors of the first and third, second and fourth transistors The pairs are connected in pairs, between the emitters of the first and second, third and fourth transistors and the output of the push-pull controlled current source, a resistor and a bias diode, respectively, are connected.