SU483765A2 - Device for automatic gain control of multichannel receiver - Google Patents

Description

one

The invention relates to radio engineering, can be used in receiving equipment.

A device for automatic gain control (AGC) of a multi-channel receiver is known. St. No. 414706, containing n receiving channels with adjustable amplifier stages at the inputs. One of the channels, the reference one, contains an automatic gain control circuit, and the adjustable amplifier stages of all channels are connected in series with each other in a series of direct current.

The purpose of the invention is to control the delay of the automatic adjustment of the gain of the main channels relative to the reference.

To do this, in the proposed device, an additional adjustable amplifier is connected to the output of the reference channel amplifier, the control input of which is connected to the control input of the amplifier of the reference channel, and the other input is supplied with a voltage from a similar input of the amplifier of the reference channel through a voltage divider.

A schematic diagram of the AGC device is shown in the drawing.

The device contains adjustable cascades of the main channels on transistors 1, 2 connected in series with direct current with an adjustable cascade of the reference channel on transistor 3. The amplification of these stages is controlled by applying AGC voltage to the base of transistor 4. Due to the differential switching of transistors 3 and 4 This current through transistors 1–3, and hence their gain, decreases when the AGC voltage exceeds the voltage at the base of transistor 4. An additional adjustable amplifier is made with a differential Heme transistors 5, 6 with a current-carrying transistor 7. Series-connected resistors 8 and 9 are included in the collector circuit of transistor 5, and a collector of transistor 6 is connected to their connection point. The base of transistor 5 is connected to the base of transistor 3 through a resistive divider 10, 11.

The device works in the following way.

The signal from the collector of transistor 3 goes to the base of transistor 7. While the AGC voltage remains less than the voltage on the bases of transistors 3 and 5, these transistors are open and their amplification is maximum, respectively, transistors 4, 6 are locked. The mixing voltage to the base of the transistor 5 is removed from the divider on the resistors 10, 11 connected between the base of the transistor 3 and the common bus. When the AGC voltage rises, transistor 6 opens first. At the same time, the current through transistor 5 decreases. When transistor 6 is fully opened and transistor 5 closes, the regulating action of the cascade stops, its gain is lower than the initial one by (R8 + R9) / R8, where Rs , Rg are the resistances of resistors 8, 9. Accordingly, the gain of the reference channel is reduced by this value. At the same time, since the gain of the transistor 3 does not change, the gain of the other channels remains unchanged.

With a further increase in the AGC voltage, the transistor 4 opens and, accordingly, the current through the transistors 3, 2, 1 begins to decrease, i.e., the gain of all the channels starts to decrease synchronously.

Subject invention

Automatic gain control device for multi-channel receiver

St. No. 414706, characterized in that, in order to control the delay of the automatic adjustment of the gain of the main channels relative to the reference, an additional is connected to the output of the reference channel amplifier

an adjustable amplifier, the control input of which is connected to the control input of the amplifier of the reference channel, and the voltage of the same input from the amplifier of the reference channel is applied to another input through a voltage divider.

Channel / Channel