| 摘要 |
PURPOSE:To realize automatic gain control by simple constitution, by executing a logical operation between A/D converting outputs of 2 phase detector outputs for detecting an orthogonal amplitude modulating signal, and obtaining a control signal of an amplitude controlling circuit. CONSTITUTION:An input signal (16QAM signal) IN is inputted to an amplitude controlling circuit 1, in which it is controlled to a prescribed level by a control signal of an output of an LPF6, and is inputted to a 16QAM demodulator 2. The 16QAM demodulator 2 detects orthogonally phase of the input signal, and outputs demodulating signals S1, S2. The demodulating signals S1, S2 are converted to signals (X1, X2, X3), (Y1, Y2, Y3) by A/D converters 3, 4. In this case, the signal X1 shows a quadrant of a receiving signal and the signal X3 shows a shift of amplitude of the receiving signal, therefore, the amplitude controlling circuit 1 is controlled by operating these signals by an EX-OR circuit 5 and obtaining an amplitude control signal without using the quadrant. |
