Self adjusting automatic gain control (AGC) power reference level circuit

摘要

Methods and apparatus for performing gain control in a manner that is designed to maximize the use of the dynamic range of signal processing circuitry, e.g., an A/D converter, while minimizing signal clipping are described. In one embodiment a power reference level used for automatic gain control purposes is periodically adjusted. An exemplary state machine of the present invention has an analysis state which collects signal statistics, e.g., signal clipping and threshold statistics, for a period of time corresponding to a fixed number of samples. During the analysis state, the number of samples that equal or exceed either the minimum or maximum valid values (e.g., clip points), supported by the signal processing circuitry, are accumulated. Statistics are also accumulated on the number of data samples that exceed thresholds, e.g., +/−tail thresholds, corresponding to points near the outer portion of the range supported by the signal processing circuitry. At the end of each analysis period, a decision is made to decrease the AGC power reference level if points were clipped, or increase the AGC power reference level if no points exceeded the tail thresholds. If neither the condition to raise nor the condition to lower the AGC power reference level is satisfied, no change is made to the power reference level. The state machine of the present invention can be used as an AGC circuit to directly control the adjustment of the gain of a signal.