| 摘要 |
PURPOSE:To prevent the change in an input impedance and to extend the range of effective operation of a double balanced type cascode amplifier, by arranging a differential amplifier for synchronizing carrier amplification using almost the same emitter electrode coupling means as that of an input differential amplifier of a double balanced type cascode amplifier constituting a video detector and an APC detector. CONSTITUTION:The emitters of a transistor(TR) pair 401, 402 of an input differential amplifying stage at the double balanced type cascode amplifier 4 in the APC phase detector are coupled directly the same as those of the video phase detector and connected to a collector electrode of a constant current TR403. An output of this APC detector, that is, an output signal obtained at a collector common connecting point of TRs 408, 410, is applied to a voltage controlled oscillator 6 via a low-pass filter 5 to make the oscillator 6 synchronize with a carrier frequency of signal input terminals 4a, 4b. The oscillator 6 is formed as a balanced output type and supplies the reproduced synchronizing carrier to a phase shifter 8 and an amplifier 9. The base electrode bias of the constant current TR903 of the amplifier 9 is supplied from a stabilized bias generator 7. Thus, since the bias current of the TR903 does not respond to the change in a power supply voltage, the impedance change of the differential pair TRs 904, 905 and the like are not produced. |
