Hysteresis-free anti-saturation circuit
First Claim
1. A method of preventing saturation in a receiver having a front-end section with a first variable-gain element, said front-end section receiving a high-frequency signal, amplifying said high-frequency signal, and converting said high-frequency signal to a lower-frequency signal, said receiver also having a back-end section for processing said lower-frequency signal, comprising the steps of:
- generating from said lower-frequency signal an indicator signal indicating a power level of said lower-frequency signal;
operating said first variable-gain element with a first gain when said indicator signal indicates that said power level is below a first threshold;
operating said first variable-gain element with a second gain, lower than said first gain, when said indicator signal indicates that said power level is above a second threshold higher than said first threshold; and
operating said first variable-gain element with at least one gain intermediate between said first gain and said second gain, when said indicator signal indicates that said power level is between said first threshold and said second threshold;
whereinas said power level increases from said first threshold to said second threshold, the gain of said first variable-gain element decreases without hysteresis from said first gain to said second gain.
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Accused Products
Abstract
An anti-saturation circuit controls the gain of a variable-gain element in the front-end section of a receiver, responsive to a desired signal strength indicated by an indicator signal. The gain of the variable-gain element varies monotonically over a certain range, being reduced as the desired signal strength increases, in order to avoid intermodulation of the desired signal with an interfering signal. If the receiver also has an automatic-gain-control circuit, the automatic-gain-control signal is adjusted to compensate for the changing gain of the variable-gain element.
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Citations
11 Claims
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1. A method of preventing saturation in a receiver having a front-end section with a first variable-gain element, said front-end section receiving a high-frequency signal, amplifying said high-frequency signal, and converting said high-frequency signal to a lower-frequency signal, said receiver also having a back-end section for processing said lower-frequency signal, comprising the steps of:
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generating from said lower-frequency signal an indicator signal indicating a power level of said lower-frequency signal; operating said first variable-gain element with a first gain when said indicator signal indicates that said power level is below a first threshold; operating said first variable-gain element with a second gain, lower than said first gain, when said indicator signal indicates that said power level is above a second threshold higher than said first threshold; and operating said first variable-gain element with at least one gain intermediate between said first gain and said second gain, when said indicator signal indicates that said power level is between said first threshold and said second threshold;
whereinas said power level increases from said first threshold to said second threshold, the gain of said first variable-gain element decreases without hysteresis from said first gain to said second gain. - View Dependent Claims (2, 3, 4)
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5. An anti-saturation circuit for a receiver having a front-end section and a back-end section, said front-end section having a first variable-gain element, said front-end section receiving a high-frequency signal, said front-end section amplifying said high-frequency signal, said front-end section converting said high-frequency signal to a lower-frequency signal, comprising:
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an indicator circuit generating an indicator signal indicating a power level of said lower-frequency signal; and a control circuit receiving said indicator signal and generating therefrom a first control signal that controls said first variable-gain element;
whereinsaid first control signal varies monotonically, assuming at least three different values, when said power level varies in a first range, and said first control signal does not vary when said power level is outside said first range. - View Dependent Claims (6, 7, 8, 9, 10, 11)
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Specification