SU886203A2 - Differential amplifier - Google Patents

Description

(54) DIFFERENTIAL AMPLIFIER

I

The invention relates to radio engineering and can be used in radio engineering devices for various purposes.

According to the main author. St. No. 598215 a differential amplifier is known, which contains input voltage followers, a preamplifier cascade, made on two transistors of opposite conductivity type connected in series over DC, whose emitters are combined and form a single cascade input, the bases are connected through a nonlinear element and form a second cascade input, and the collectors are connected to the inputs of the output push-pull cascade 1J.

However, the known differential amplifier has a relatively low stability of the mode. direct current.

The purpose of the invention is to increase the stability of the DC mode.

The goal is achieved by the fact that an additional cascade is introduced into the differential amplifier, containing two transistors of the opposite conductivity type connected in series in DC, the bases and the collectors of which are connected to the respective bases and

collectors-transistors of the preliminary cascade, and the emitters are combined and through the resistance are connected to the output of the amplifier.

The drawing shows the structural electrical circuit of the proposed differential amplifier.

The differential amplifier contains input repeaters I n 2 voltages, preamplifier stage on transistors 3 and 4, additional stage on transistors 5 and 6, non-linear element 7.10, output push pull stage 8, and resistance 9.

The amplifier works as follows.

In the absence of a signal at the amplifier inputs at the outputs of the input repeaters I and 2, the signal is also absent. In this case, the potential difference between the outputs of the input repeaters 1 and 2 is determined only by the voltage drop at the base-emitter transitions of the transistors 3 and 4, the collector currents of which in this mode and

20, their value is determined by the current flowing through the nonlinear element 7. If the collector currents of transistors 5 and 6 are equal in this case, then the current flowing into one of the

the inputs of the two-stage vykhbdnogo cascade 8, is equal to the current flowing from its second output, which provides a zero voltage at the output of the amplifier, which through the resistance 9 goes to the emitters of trans-, resistors 5 and 6. Any change in the output voltage of the amplifier leads to inequalities and the resulting input currents of the output push-pull stage 8, which causes a change in the output voltage of the amplifier, the opposite of the original. When a signal is applied to the amplifier inputs, the input voltage is transmitted by input repeaters I and 2 and is applied between the bases and emitters of transistors 3 and 4, causing the difference in their collector currents L1, the value of which is equal.

 exit i

where l / bjt input differential signal Rgyji is the output impedance of the input

Repeater 1.

The resulting voltage Ugy at the output of the amplifier leads to the formation of the difference between the collector currents of the transistors 5 and 6 Alj, the value of which is determined from the expression

. ,

where RO is the resistance 9. The difference in the input currents is converted by the output two-stage cascade 8 to the output voltage Uv. equal to

ey) (Lr) Z,

where Z is the input impedance of the output push-pull stage 8, which determines the gain of the open (in the absence of impedance 9) amplifier.

The use of a field-effect transistor as a junction 9 allows adjustment of the gain of the amplifier by changing the voltage across its gate.

The proposed amplifier has a high gain stability and can be used in systems with automatic gain control.

Claims (1)

Invention Formula Differential amplifier auth. St. NO 598215, characterized in that, in order to increase the stability of the regime by DC, an additional cascade is introduced into it containing two DC-connected transistors of the opposite conductivity type, the bases and the collectors of which are connected to the corresponding bases and collectors of the preliminary cascade transistors, and the emitters are connected and are connected via an impedance to the output. Amplifier. Sources of information taken into account in the examination 1- USSR author's certificate No. 598215, cl. H 03 F 3/45, 1975 (prototype).