Automatic gain control

. يناير 19, 2021

A.C.G

(Automatic gain control)

The automatic gain control microphones come with a built-in preamplifier producing line level audio output.Automatic gain control (A.G.C.) automatically converts the receiver's gain according to the strength of the signal received by the antenna.

Schematic of AGC used in analog telephone networks; The gain response from the output level is effected through a vectrol resistive opto-isolator.

Since the amplitude of the signal received by the antenna always changes. Hence A. F. C . Circuit I. F. And R. F. This is how we convert the gain of the stage. That the voltage level at the input of the video detector always remain the same. Since the gain of the amplifying device can be changed by changing the operating point, and the operating point can be changed by changing the bias voltage.

The gain of the vacuum tube and the field effect transistor can be given by the following equation.

Where:

Au = gm. ZL

Au =voltage gain of the amplified device

gM =trans conductance of the device

The value of load impedance is determined by the component used in the tuve circuit.

Since the amplitude of the synchronization signal received with the composite video signal with the variation in the picture signal is always unchanged. Hence, the top level of the synchronization pulse represents the signal strength. A control voltage is developed using a peak rectifier. It is then filtered and F . And I. F . The input bias of the amplifier is fed onto the circuit, so that R. F . And I. F . (RE. And IF.) Amplifier gain can be controlled.

How it works:-

The signal to be controlled (the detector output in a radio) goes to a diode and capacitor, which produces a peak-following DC voltage. This is fed to RF gain blocks to alter their gain, thus changing their gain. Traditionally all gain-controlled phases preceded signal detection, but it is possible to improve gain control by adding a gain-controlled phase to detect the signal.

What is the benefit of using automaticgain control

By performing an automatic gain control (A.G.C.), the picture intensity remains unchanged even if the input signal strength changes. a . G. C . The circuit reduces the gain of the receiver circuit as the signal strength increases. Therefore, when the receiver is changed from one station to another, the contrast of the reproduced picture remains unchanged, and its other advantage is that the gain of strong signal is reduced in gain. ) Can be overcome by cross modulation distortion.