MULTIBAND LOCAL OSCILLATOR

摘要

A multiband local oscillator of a television tuner comprises a common collector transistor amplifier, a capacitive feedback circuit for conditioning the amplifier to oscillate in the wide range of frequencies for VHF broadcast and cable channels and a multiband tuning circuit coupled to the base electrode of the transistor. Bandswitching signals are applied to the multiband tuning circuit to produce tuned circuit configurations for the various frequency bands. When one band is selected, the corresponding bandswitching signal is coupled to the capacitive feedback network to modify it so as to inhibit out-of-band oscillations due to parasitic elements of the tuning circuit.