What is automatic gain control (AGC). how Can i design it?

Automatic gain control (AGC) is an adaptive system found in many electronic devices. The average signal level is used to adjust the gain to an appropriate level for a range of input signal levels. For example, without AGC the sound emitted from an AM radio receiver would vary to an extreme extent from a weak to a strong signal; the AGC effectively reduces the volume if the signal is strong and raises it when it is weaker.





A very common and typical example is the AGC used in AM radio. Such a receiver is essentially linear鈥攖he sound volume is proportional to the radio signal strength, because the information content of the signal is carried by the changes of amplitude of the carrier wave. If the circuit were not linear, the modulation could not be recovered with reasonable fidelity. However, the strength of the signal received will vary widely, depending on the power and distance of the transmitter, and signal path attenuation. The AGC circuit keeps the receiver in its linear operating range by detecting the overall strength of the signal and automatically adjusting the gain of the receiver to maintain an approximately constant average output level. For a very weak signal the AGC has no effect; as the signal increases, the AGC reduces the gain.





It is usually disadvantageous to reduce the gain of the front end of the receiver on weaker signals as this can worsen signal-to-noise ratio and blocking rejection. Many designs reduce the gain of the first stage only for stronger signals, known as a delayed AGC circuit.





FOR DESIGN SEE THE FOLLOWING URL:


http://www.eecg.utoronto.ca/~kphang/pape鈥?/a>

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