Variable tuning circuit using variable capacitance diode and television tuner

Abstract

The invention provides a variable tuning circuit capable of extending a variable range in a high frequency band, ensuring the value of L of an inductor to increase the value of Q of a circuit in a low frequency band, and preventing a reduction in gain, an increase in noise, and unstable oscillation. A variable tuning circuit includes: a first parallel resonance circuit that includes a varactor diode, a capacitor connected in series to the varactor diode, and a first inductor connected in parallel to the varactor diode and the capacitor; and a second parallel resonance circuit that includes a second inductor connected in parallel to the varactor diode with a direct current cut-off capacitor interposed therebetween. When the varactor diode has a maximum capacitance, a resonant frequency of the second parallel resonance circuit is set about a lowest frequency in a variable frequency range.

Dependencies are inferred from the claim text.