| 摘要 |
PURPOSE:To simplify the constitution of a detecting circuit and also to attain the working of said circuit with a low level of voltage, by using a muting control circuit to control the working current of a detector whose detection gain is controlled by the increment/decrement of the working current. CONSTITUTION:An FM signal serving as a switching signal is applied via a phase shifter to terminals 4 and 6 of a detector 2 constituting a quadrature detector. While the FM signal to undergo detection is applied directly to terminals 8 and 10 respectively. When a control signal VC is applied to a terminal 18 of a muting control circuit 16, the current flowing to a transistor (TR)80 is supplied to TRs 40 and 42 via current inverting circuits 58 and 60 respectively by a current Mirror effect and then flows into a constant current source 44. Therefore the currents of differential amplifiers 20 and 22 of the detector 2 are increased and decreased in response to the current supplied from the circuit 16. The gains of amplifiers 20 and 22 are proportional to the working current. Thus the detection gain of the detector 2 receive the muting control from the circuit 16, and the output of the detector 2 is extracted out of a terminal 14 via an output circuit 12. |
