Automatic gain control circuit with non-negative exponential release
First Claim
1. An automatic gain control (AGC) circuit for providing gain-controlled signal at an output related to signals received at an input, comprising:
- gain-controllable amplifier means having an output coupled to the AGC output;
means couplng the AGC input to an input of said amplifier means; and
gain control means responsively coupled to receive signals from within the AGC circuit for automatically determining whether the gain should be increased or decreased, and for controlling said amplifier means with control signals which progressively increase in increasingly larger magnitudes, at least initially, if the gain should be increased, and which decrease if the gain should be decreased.
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Accused Products
Abstract
An automatic gain control circuit wherein the gain progressively increases in increasingly larger magnitudes. The illustrative embodiment includes an amplifier whose gain is related by a voltage follower to the voltage on a capacitor in a feedback loop. A rectifier develops a signal representing the AGC output level which is compared against a threshold value. A current source, arranged in a further feedback loop with the capacitor and the voltage follower, increases the voltage on the capacitor as a function of that voltage. The second derivative with respect to time of such function is non-negative. To ensure that there exists a voltage on the capacitor upon which the current source can operate, a starting circuit provides a small, non-zero voltage to the capacitor.
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Citations
19 Claims
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1. An automatic gain control (AGC) circuit for providing gain-controlled signal at an output related to signals received at an input, comprising:
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gain-controllable amplifier means having an output coupled to the AGC output; means couplng the AGC input to an input of said amplifier means; and gain control means responsively coupled to receive signals from within the AGC circuit for automatically determining whether the gain should be increased or decreased, and for controlling said amplifier means with control signals which progressively increase in increasingly larger magnitudes, at least initially, if the gain should be increased, and which decrease if the gain should be decreased. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. In an automatic gain control circuit of the type having an input for receiving signals, a gain-controllable amplifier means for providing adjusted gain signals to an output, and a feedback circuit coupled to the AGC output and having a capacitor therein, the feedback circuit controlling the gain of the amplifier in accordance with the voltage on the capacitor, the feedback circuit having means for discharging the capacitor substantially only if the output signal exceeds a predetermined threshold value, and having means for charging the capacitor, the improvement comprising:
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means for ensuring that a small but nonzero voltage will be on the capacitor; and means associated with the feedback circuit for increasing the voltage on the capacitor as a function of the voltage thereon, the second derivative of said function with respect to time being non-negative. - View Dependent Claims (12, 13, 14, 15)
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16. A method for automatic gain control of a signal level comprising:
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automatically determining whether the signal level should be increased or decreased; if the signal level should be increased, then adjusting the gain so that its second derivative with respect to time, at least initially, is positive; and if the signal level should decrease, then decreasing the signal level. - View Dependent Claims (18, 19)
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17. A method for automatic gain control of a signal level comprising:
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automatically determining whether the signal level should be increased or decreased; if the signal level should be increased, then progressively increasing the gain in increasingly larger amounts for selected times; if the signal level should be decreased, then decreasing the gain.
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Specification