TUNING CIRCUIT FOR A MULTIBAND TUNER

摘要

A multiband local oscillator of a television tuner comprises a common collector transistor amplifier, a feedback circuit for conditioning the amplifier to oscillate in the wide range of frequencies for VHF broadcast and cable channels and a tuning circuit coupled to the base electrode of the transistor. Bandswitching signals are applied to switching diodes in 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 switching diode associated with a lower band to turn it on as well as the switching diode for the selected band to inhibit out-of-band oscillators due to parasitic elements of the tuning circuit.