| 摘要 |
PURPOSE:To increase input-output isolation of the whole phase modulator by providing a zero setting circuit which makes a signal voltage from a driving circuit zero when a carrier cut-off signal is applied. CONSTITUTION:Diode switch circuit 10 is a five-stage low-pass filter type switch circuit using PIN diodes 12 and 14; when voltages differing in direction are applied to diodes 12 and 14 from control circuit 16, the switch turns on and when forward voltages are applied, diodes 12 and 14 conduct to form a short circuit, thereby cutting off a carrier. Control circuit 16 applies the forward voltages to diodes 12 and 14 applied with a carrier cut-off signal. Driving circuit 30, when the carrier cut-off signal is applied via line 40, controls forcibly a voltage signal to be supplied two- phase PSK modulator 20 to zero. |
