SU1239838A1 - Amplifier with adjustable gain factor - Google Patents

Abstract

The invention relates to radio engineering. The adjustment range is resolved. The device contains an operative amplifier (OA) 1, an input resistor (P) 2, three field transistors (PT), 3.5 and 8, P 4 and two additional P 6 and 7. In the case where the PT 5 is closed and the PT 3 and 8 are open, i.e. in the case of a minimum gain factor, the resistance in the negative feedback circuit of the op-amp 1 will be determined by the sum of the coft of the motivations of the open PT 3 and 8 channels, which expands the control range. The goal is achieved by the introduction of PT B. 1 cl. B) J6-- g 5 f you) o & - (L with N go with so 00 oo 00

Description

eleven

The invention relates to radio engineering and can be used in devices for automatic adjustment, amplification and other devices where amplifiers with a controlled non-transmission coefficient are needed.

The purpose of the invention is to expand the range of adjustment.

The drawing shows a high voltage electrical amplifier circuit with adjustable gain.

The circuit contains the operational amplifier 1, the input resistor 2, the first field-effect transistor 3, the resistor 4, the second field-effect transistor 5, the first 6 and second 7 additional resistors and the third field-effect transistor 8.

The amplifier with adjustable gain operates as follows.

When a signal is applied to its input, the level of the output signal is determined by the transfer coefficient of the amplifier, which depends on the resistance of the FET channels. The resistance of the field-effect transistors is determined by the driver on its gate.

The gain of the amplifier will be minimal when the first field effect transistor 3 and the third field effect transistor 8 are open and the second field effect transistor 5 is closed. In this case, only negative feedback acts, which determines the parallel connection of the first additional resistor 6 and the sum of the resistances of the channel of the first field-effect transistor 3 and the parallel connection of the channel of the third field voltage of the resistor 8 and resistor 4. Since the resistance of the open channel of the third field-effect transistor 8 is much less the resistance of the resistor 4, as well as the first additional resistor 6, the resistance in the negative feedback circuit will be determined by the sum of the resistances of the channels field effect transistors 3 and 8.

As the field-effect transistors 3 and 8 block up, the resistance of their channels increases and the magnitude of the negative feedback will decrease. At the same time, the resistance of the channel of the second field-effect transistor 5 will decrease, since the gate of the field t-ranzors 3 and 5 is supplied by the anti-fi e: ZN control voltages and the magnitude of the positive feedback will increase, which will increase the gain of the amplifier.

. The magnitude of the positive feedback will be determined by the ratio of the shoulders

five

0

bodies consisting of a parallel connection of the channel of the third field-effect transistor 8 and resistor 4, as well as the channel of the second field-effect transistor 5 and the second additional resistor 7.

The gain will be maximum when the field-effect transistors 3 and 8 are closed, and the second field-effect transistor 5 is opened.

In this case, the negative feedback will be determined by the resistance of the first additional resistor 6, and the positive feedback will be determined by the ratio of the resistances of resistors 4 and 7, since the resistance value of the parallel connection of resistor 4 and the channel of the third field-effect transistor 8 the strength of the large value of the channel resistance of the closed third field-effect transistor 8.

So, when the second field-effect transistor 5 is closed and the field-effect transistors 3 and 8 are open, i.e. at the minimum gain factor, the resistance in the circuit is denied by the amplifier feedback, h will be determined by the sum of the resistances of the channels of the open field-effect transistors 3 and 8, therefore, the control range is expanded.

thirty

Claims (1)

Invention Formula five 0 five 0 five An adjustable gain amplifier containing a series-connected input resistor and an operational amplifier, between the output and inverting input of which is connected) is a series-connected resistor and the first field-effect transistor and the first additional resistor, and between the resistor connected and the common bus connection of the one line and the common bus. In series, connect the second field effect transistor and the second additional resistor, the junction point of which is connected to the non-inverting the input of the operational-amplifier, and the gates of the first and second field-effect transistors are the inputs for the supply of antiphase control siptal, about t and ch- and so that, in order to expand the dial; the point of connection of the first and second field-effect transistors and the output of the operational amplifier are switched on by the source and drain, respectively, the third field-effect transistor, the gate of which is connected to the gate of the first field-effect transistor.