Automatic gain control
First Claim
1. An automatic gain control circuit comprising:
- means for amplifying an input signal to develop a first signal;
means for generating a second signal to control the gain of said amplifying means;
means responsive to said first signal and to a predetermined reference voltage level for providing to said generating means a first logic signal when said first signal is greater in amplitude than said predetermined reference voltage level and a second logic signal when said first signal is lower in amplitude than said predetermined reference voltage level, said generating means being responsive to said first logic signal for causing said second signal to vary in a first direction to reduce the gain of said amplifying means and being responsive to said second logic signal for causing said second signal to vary in a second direction to increase the gain of said amplifying means; and
means, responsive to said first logic signal when its duration is longer than a first predetermined time period, for causing said generating means to prevent said second signal from varying in the first direction for a second predetermined time period, thereby inhibiting any reduction in gain of said amplifying means during the second predetermined time period.
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Accused Products
Abstract
An automatic gain control circuit suitable for use in a modem receiver for receiving a modulated carrier representing data, includes a variable gain amplifier adapted to receive an input signal and coupled to an output amplifier providing the gain controlled output and also coupled to a level detector which provides a high level output signal whenever the input thereto exceeds a reference level, such output signal causing an attack operation wherein a control current generator provides an exponentially decreasing control current for an operational transconductance amplifier included in the variable gain amplifier. When the level detector output is high for more than a predetermined time a noise hit protection circuit is effective to inhibit the attack operation for a further predetermined period of time, thereby alleviating the adverse effect of a noise pulse.
43 Citations
10 Claims
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1. An automatic gain control circuit comprising:
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means for amplifying an input signal to develop a first signal; means for generating a second signal to control the gain of said amplifying means; means responsive to said first signal and to a predetermined reference voltage level for providing to said generating means a first logic signal when said first signal is greater in amplitude than said predetermined reference voltage level and a second logic signal when said first signal is lower in amplitude than said predetermined reference voltage level, said generating means being responsive to said first logic signal for causing said second signal to vary in a first direction to reduce the gain of said amplifying means and being responsive to said second logic signal for causing said second signal to vary in a second direction to increase the gain of said amplifying means; and means, responsive to said first logic signal when its duration is longer than a first predetermined time period, for causing said generating means to prevent said second signal from varying in the first direction for a second predetermined time period, thereby inhibiting any reduction in gain of said amplifying means during the second predetermined time period. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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Specification