Patent ID: 7363015

Claim:
A television tuner comprising: a tuning circuit for tuning a television signal, the tuning circuit comprising a first varactor diode for changing a tuning frequency; a mixer for converting a television signal output from the tuning circuit to an intermediate frequency signal; an oscillator for supplying a local oscillating signal to the mixer, the oscillator comprising a second varactor diode for changing an oscillating frequency; and a PLL circuit for outputting a tuning voltage for tuning the television signal; wherein the tuning voltage is applied to cathodes of the first varactor diode and the second varactor diode and wherein voltages of anodes of the first varactor diode and the second varactor diode are higher at a time of receiving the television signal whose frequency is lower than or equal to a predetermined frequency than at a time of receiving a television signal whose frequency is higher than the predetermined frequency; a transistor for switching voltages of the anodes of the first varactor diode and the second varactor diode; wherein a collector of the transistor is pulled up to a predetermined voltage, an emitter of the transistor is connected to ground, the anodes of the first varactor diode and the second varactor diode are connected to the collector of the transistor by the corresponding first resistors, the anodes of the first varactor diode and the second varactor diode are also connected to ground for a direct current by the corresponding second resistors, the transistor is turned on when receiving the television signal whose frequency is higher than the predetermined frequency, and the transistor is turned off when receiving the television signal whose frequency is lower than or equal to the predetermined frequency.