| 摘要 |
PURPOSE:To obtain a stable phase modulator against temperature change, secular change and frequency change by using an automatic level control circuit so as to control an output level. CONSTITUTION:A part of an output of an amplifier 10 is extracted and inputted to a detection circuit 12, where an output signal level is converted into a DC voltage. The detection output of the circuit 12 corresponds to a QPSK modulator output level and the fluctuation of the QPSK modulator output level is detected as the fluctuation of the detected output. The detected output is inputted to a voltage comparison/integrator 13, compared with an output level control voltage from a terminal 21, the difference is amplified and integrated and fed back to a variable attenuator 9. As a result, the automatic level control circuit is constituted, where the output level control voltage is used as a reference. The correction to each circuit is not required for temperature and frequency change and only the temperature characteristic of the DC conversion of the detection circuit has only to be compensated. |
