# US 6,721,017 B2 · Television tuner's intermediate frequency tuning circuit capable of receiving FM broadcast signals

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- Number: US 6,721,017 B2
- Document ID: US6721017B2
- Status: Granted
- Kind: B2
- Application number: 09/862,239
- Filed: 2001-05-22
- Published: 2001-12-06
- Granted: 2004-04-13
- Earliest claimed: 2000-05-26
- Assignees: Alps Electric Co., Ltd.
- Inventors: Masaki Yamamoto
- Web page: https://patentgrep.com/patent/US6721017B2

## CPC

- H03J 5/244: {using electronic means}
- H03J: TUNING RESONANT CIRCUITS; SELECTING RESONANT CIRCUITS

## Abstract

The present invention realizes a small-size and inexpensive television tuner's intermediate frequency tuning circuit that can be used for both television intermediate frequency signals and FM broadcast signals frequency-converted to 10.7 MHz. The television tuner's intermediate frequency tuning circuit comprises: a parallel tuning circuit to both ends of which a television intermediate frequency signal or an FM broadcast signal frequency-converted to 10.7 MHz is inputted; a series tuning circuit connected in parallel to the parallel tuning circuit; and a switch, connected in parallel to a capacitive element of the series tuning circuit, that is closed when the intermediate frequency signal is inputted, and opened when the FM broadcast signal is inputted, wherein the respective tuning frequencies of the parallel tuning circuit and the series tuning circuit are set to 10.7 MHz or more; when the switch is closed, a parallel tuning frequency produced by the parallel tuning circuit and the series tuning circuit is set to the frequency of the intermediate frequency signal; and when the switch is opened, the parallel tuning frequency is set to 10.7 MHz.

## Claims

### Claim 1

A television tuner's intermediate frequency tuning circuit, comprising:
a parallel tuning circuit, comprising a first inductance element and a first capacitive element, to both ends of which one of a television intermediate frequency signal and an FM broadcast signal frequency-converted to 10.7 MHz is inputted, the both ends being respectively connected to both ends of a load;
a series tuning circuit, comprising a second inductance element and a second capacitive element, connected in parallel to the parallel tuning circuit; and
a switch, connected in parallel to the second capacitive element, that is closed when the intermediate frequency signal is inputted, and opened when the FM broadcast signal is inputted, wherein:
respective tuning frequencies of the parallel tuning circuit and the series tuning circuit are set to at least 10.7 MHz;
when the switch is closed, a parallel tuning frequency produced by the parallel tuning circuit and the series tuning circuit is set to a frequency of the intermediate frequency signal; and
when the switch is opened, the parallel tuning frequency is set to 10.7 MHz.

### Claim 2 (depends on 1)

The television tuner's intermediate frequency tuning circuit according to claim 1, wherein:
the first inductance element comprises two first small inductance elements connected in series, and a first voltage is applied to a connection point between the two first small inductance elements;
the second inductance element comprises two split second small inductance elements, and the second capacitive element is connected between the two second small inductance elements;
the switch comprises first and second switch diodes having cathodes connected with each other;
when the intermediate frequency signal is inputted, the voltages of the cathodes are dropped below the first voltage, and the first and second switch diodes are turned on; and
when the FM broadcast signal is inputted, voltages of the cathodes are raised above the first voltage, and the first and second switch diodes are turned off.

### Claim 3 (depends on 2)

The television tuner's intermediate frequency tuning circuit according to claim 2, wherein:
there are provided a first varactor diode to couple one end of the parallel tuning circuit to one end of the load, and a second varactor diode to couple the other end of the parallel tuning circuit to the other end of the load;
an anode of the first varactor diode is connected to the one end of the parallel tuning circuit, and an anode of the second varactor diode is connected to the other end of the parallel tuning circuit;
when the intermediate frequency signal is inputted, voltages of cathodes of the first and second varactor diodes are dropped below the first voltage, and the first and second varactor diodes are turned on; and
when the FM broadcast signal is inputted, the voltages of the cathodes are raised above the first voltage, and the first and second varactor diodes are turned off.