IF circuit with reduced sound attenuation for cable signals

摘要

A cable-ready television receiver including a tuner switchable between cable and off-air signals has an LC trap tuned to the audio carrier frequency coupled between the tuner and a SAW IF amplifier. The trap includes a varactor diode that, when it exhibits a large capacitance, effectively disables the trap. This occurs when the receiver is used with cable signals. In the event the receiver is used for off-air signals, the voltage applied to the varactor diode causes it to exhibit a much smaller capacitance which effectively enables the trap.