# US 7,609,134 B2 · Variable tuning circuit using variable capacitance diode and television tuner

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- Number: US 7,609,134 B2
- Document ID: US7609134B2
- Status: Granted
- Kind: B2
- Application number: 11/940,972
- Filed: 2007-11-15
- Published: 2008-06-05
- Granted: 2009-10-27
- Earliest claimed: 2006-12-05
- Assignees: Alps Electronic Co., Ltd.
- Inventors: Masaki Yamamoto
- Web page: https://patentgrep.com/patent/US7609134B2

## CPC

- H03J 3/185: {with varactors, i.e. voltage variable reactive diodes}
- H03J 3/06: Arrangements for obtaining constant bandwidth or gain throughout tuning range or ranges
- H03J 3/26: the circuits being coupled so as to form a bandpass filter
- H03J: TUNING RESONANT CIRCUITS; SELECTING RESONANT CIRCUITS

## 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.

## Claims

### Claim 1

A variable tuning circuit comprising:
a first parallel resonance circuit that includes a variable capacitance element, a capacitor connected in series to the variable capacitance element, and a first inductor connected in parallel to the variable capacitance element and the capacitor; and
a second parallel resonance circuit that includes a second inductor connected in parallel to the variable capacitance element in an AC manner,
wherein, when the variable capacitance element has a maximum capacitance, a resonant frequency of the second parallel resonance circuit is set about a lowest frequency in a variable frequency range.

### Claim 2 (depends on 1)

The variable tuning circuit according to claim 1,
wherein, when the variable capacitance element has a minimum capacitance, the resonant frequency of the second parallel resonance circuit is set so as to be higher than a highest frequency within a variable frequency range in a high frequency band.

### Claim 3 (depends on 1)

A television tuner comprising the variable tuning circuit according to claim 1 in at least one of an input tuning circuit, a single inter-stage tuning circuit, and an oscillating circuit.