Method and apparatus for reducing intermodulation distortion in a low current drain automatic gain control system
AssigneeMotorola, Inc.
InventorJames David Hughes
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Abstract
An apparatus for reducing intermodulation distortion in a low current drain automatic gain control system includes a multiplier (1500) and an AGC digital signal processor (1100).
Claims13
A low current drain automatic gain control system, comprising:
- a low current drain low noise amplifier (LNA) that has an intermodulation third order intercept point (IP3) that varies with a gain of the LNA such that there exists a significant peak of the IP3 between a minimum gain and a maximum gain of the LNA;
- and
- a gain controller that controls the gain of the LNA such that the gain is limited to a predetermined value substantially at the significant peak of the IP3, the limit being imposed between the value and one of the minimum and maximum gains.
A method used in a receiver comprising a low current drain low noise amplifier (LNA) that has an intermodulation third order intercept point (IP3) that varies with a gain of the LNA such that there exists a significant peak of the IP3 between a minimum gain and a maximum gain of the LNA, the method comprising the steps of:
- determining a signal power of a recovered signal;
- decreasing a gain value when the signal power is above a predetermined AGC threshold;
- and
- setting the gain value to a predetermined gain limit when the gain value is below a predetermined gain limit.
A method used in a receiver comprising a low current drain low noise amplifier (LNA) that has an intermodulation third order intercept point (IP3) that varies with a gain of the LNA such that there exists a significant peak of the IP3 between a minimum gain and a maximum gain of the LNA, the method comprising the steps of:
- determining a signal power of a recovered signal;
- determining a signal spectrum of the recovered signal when the signal power is above a predetermined AGC threshold;
- spectrally testing the signal spectrum for an intermodulation signal power;
- decreasing a gain value using a stored gain response;
- and
- setting the gain value to a predetermined gain limit when the intermodulation signal power is above a predetermined IM threshold and the gain value has been decreased below a predetermined gain limit in the step of decreasing the gain value.
Dependencies are inferred from the claim text.