| 摘要 |
PURPOSE:To make the amplitude of a base band signal constant by executing a gain control so that the amplitude of a first and a second base band signals are proportional to a square of the amplitude of a first and a second intermediate frequency (IF) signals, and also, the amplitude of the base band signal after the synthesis becomes constant, and thereafter, synthesizing them. CONSTITUTION:A control part 12 detects the amplitude of IF signals 8, 9, and executes a control so that they are inputted to demodulating parts 15, 16 with constant amplitude by adjusting the gain of variable gain regulators 13, 14. In the demodulating parts 15, 16, the IF signals 8, 9 are demodulated to base band signals 17, 18, respectively. Subsequently, the base band signals 17, 18 are adjusted as to the amplitude by variable gain regulators 19, 20, and thereafter, synthesized by a synthesizer 21, and in this case, the amplitude of a first and a second base band signals 17, 18 are adjusted so that it is proportional to a square of the amplitude of a first and second IF signals 8, 9, respectively, and also, the amplitude of a base band signal 22 after the synthesis becomes constant. In such a way, the base band signal of constant amplitude is obtained irrespective of intensity of a received signal light. |
