TV receiver tuner with blocking amplifier - has amplifier between front end and mixer to prevent mixer sideband feedback

摘要

The tuner is for a TV receiver and has a tunable input stage and a tunable bandpass filter, but between the output of the filter and the mixer stage is an amplifier to prevent interfering sidebands from the mixer stage feeding back to input stages. This design enables a wider band pass filter and input stage to be used, together with compatible bandwidth in the mixer stage. The tuner comprises antenna input (1) into the tunable input stage and a dual-gate MOS FEt (T1, 3) followed by the tunable bandpass filter (4). The filter output is fed to the amplifying feedback prevention circuit (5) which may be either a dual-gage MOSFET or a high current unregulated transistor. The output of this stage is commoned with the local oscillator (7) output and fed into a further dual-gate MOSFET stage (T3, 6) on the output of which appears the IF (8). The tuner is primarily intended for the reception of signals in the VHF band.