OFDM receiver and its automatic gain control circuit

An automatic gain controller circuit in an OFDM receiver for receiving and demodulating an orthogonal frequency division multiplexing (OFDM) signal, comprising:

• clip detection means for comparing a clip number threshold value with a detected number of transient clips in which a signal level of the intermediate frequency signal exceeds a parameter clip level, so as to detect a period where the detected number exceeds the clip number threshold value,
• accumulator means for accumulating a detection output of the clip detection means, and
• target value decision means to which an accumulation output of the accumulator means is supplied;
• wherein the target value decision means includes
• first comparison means for comparing the accumulation output of the accumulator means with a clip threshold value to judge if a clip occurs, and
• second comparison means for comparing the accumulation output of the accumulator means with a non-clip threshold value to judge whether a clip does not occur;
• wherein a target value for automatic gain control is adaptively determined by decreasing the target value by a predetermined amount in accordance with a comparison output of the first comparison means and by increasing the target value by a predetermined amount in accordance with a comparison output of the second comparison means.

An OFDM receiver for receiving and demodulating an orthogonal frequency division multiplexing (OFDM) signal, comprising:

• a variable gain amplifier controlling a signal level of an intermediate frequency signal that is obtained from a reception signal by frequency-conversion;
• and
• an automatic gain controller controlling a gain of the variable gain amplifier;
• wherein the automatic gain controller includes
• a clip detector comparing a clip number threshold value with a detected number of transient clips in which a signal level of the intermediate frequency signal exceeds a parameter clip level, so as to detect a period where the detected number exceeds the clip number threshold value,
• an accumulator accumulating a detection output of the clip detector, and
• a target value decision circuit to which an accumulation output of the accumulator is supplied;
• wherein the target value decision circuit includes
• a first comparator comparing the accumulation output of the accumulator with a clip threshold value to judge if a clip occurs, and
• a second comparator comparing the accumulation output of the accumulator with a non-clip threshold value to judge whether a clip does not occur;
• wherein a target value for automatic gain control is adaptively determined by decreasing the target value by a predetermined amount in accordance with a comparison output of the first comparator and by increasing the target value by a predetermined amount in accordance with a comparison output of the second comparator.