A dual mode tuner/receiver is disclosed in which both analog and digital
signals can be received and processed. A low pass filter allows all
channels below a selected frequency enter the circuit. A precisely
controlled dual conversion circuit creates an intermediate frequency (IF)
signal. An automatic carrier detection circuit monitors the IF signal and
determines whether the signal is of analog or digital format and
intermediate frequency filters are adjusted based upon the type of signal
detected. A coherent oscillator circuit generates in-phase and quadrature
reference signals that are used by video and audio detectors for further
processing of the IF signal. In-phase and quadrature outputs are provided
for digital signals and composite video and audio outputs are provided
for analog signals.