Television tuner capable of receiving FM broadcast

There is provided a television tuner which is small and inexpensive, so that although a television signal and an FM broadcast signal have different electric field strengths in band and signal, one circuit can receive both the television signal and the FM broadcast signal. A television signal is frequency-converted to the intermediate-frequency band of a television. An FM broadcast signal is frequency-converted to a voice intermediate frequency in the intermediate-frequency band. A first parallel tuned circuit and a second parallel tuned circuit are connected in parallel with each other in an intermediate-frequency tuned circuit. When the television signal is received, the television signal is tuned to a broad band by only the first parallel tuned circuit. When the FM broadcast signal is received, the FM broadcast signal is tuned to a narrow band by the first parallel tuned circuit and the second parallel tuned circuit.

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What is claimed is:

1. A television tuner comprising: a mixer to be fed on of a television signal and an FM broadcast signal to frequency-convert the television signal to anintermediate-frequency band of a television, and frequency-convert he FM broadcast signal to a voice intermediate frequency in the intermediate-frequency band; and an intermediate-frequency tuned circuit provided at a later stage than the mixer, whereinthe intermediate-frequency tuned circuit comprises a first parallel tuned circuit tuned to a frequency substantially in a center of the intermediate-frequency band, a second parallel tuned circuit tuned to a frequency lower than the voice intermediatefrequency, and a switch connected in series with the second parallel tuned circuit, a signal of the intermediate-frequency band and a signal of the voice intermediate-frequency band are applied to both ends of the first parallel tuned circuit and bothends of a series circuit comprising the second parallel tuned circuit and the switch, when the television signal is received, the switch is brought into an off state, when the FM broadcast signal is received, the switch is brought into an on state, sothat a parallel circuit comprising the first tuned circuit and the second tuned circuit is tuned to the voice intermediate frequency.

2. A television tuner comprising: a mixer to be fed one of a television signal and an FM broadcast signal to frequency-convert the television signal to an intermediate-frequency band of a television, and frequency-convert the FM broadcast signalto a voice intermediate frequency in the intermediate-frequency band; and an intermediate-frequency tuned circuit provided at a later stage than the mixer, wherein the intermediate-frequency tuned circuit comprises a first parallel tuned circuit, asecond parallel tuned circuit, and a first varactor diode connected in series with the second parallel tuned circuit, a parallel tuning frequency of either of the first parallel tuned circuit and the second parallel tuned circuit is set to be higher thana frequency in a center of the intermediate-frequency band, and a parallel tuning frequency of the other tuned circuit is set to be lower than the voice intermediate frequency, the signal of the intermediate-frequency band and the signal of the voiceintermediate-frequency band are applied to both ends of the first parallel tuned circuit and both ends of a series circuit comprising the second parallel tuned circuit and the first varactor diode, when the television signal is received, a reverse biasvoltage is applied to the first varactor diode, so that the second parallel tuned circuit and the first varactor diode are series-tuned to the frequency of the intermediate-frequency band corresponding to an image carrier of a higher side televisionchannel adjacent to a television channel to be received, and a parallel circuit of the second parallel tuned circuit and the first varactor diode connected in series, and the first parallel tuned circuit is tuned to the intermediate-frequency band, whenthe FM broadcast signal is received, the first varactor diode is brought into a conductive state, so that a parallel circuit comprising the first parallel tuned circuit and the second parallel tuned circuit is tuned to the voice intermediate-frequency.

3. The television tuner according to claim 1, further comprising an intermediate-frequency amplifier provided at a later stage than the mixer, and a series tuned circuit connected between an output end and the ground of theintermediate-frequency amplifier, wherein the series tuned circuit has a midpoint as an output end, a tuning frequency of the series tuned circuit is changeable, when the television signal is received, the tuning frequency of the series tuned circuit isoutside the intermediate-frequency band, when the FM broadcast signal is received, the tuning frequency of the series tuned circuit is tuned to the voice intermediate frequency.

4. The television tuner according to claim 2, further comprising an intermediate-frequency amplifier provided at a later stage than the mixer, and a series tuned circuit connected between an output end and the ground of theintermediate-frequency amplifier, wherein the series tuned circuit has a midpoint as an output end, a tuning frequency of the series tuned circuit is changeable, when the television signal is received, the tuning frequency of the series tuned circuit isoutside the intermediate-frequency band, when the FM broadcast signal is received, the tuning frequency of the series tuned circuit is tuned to the voice intermediate frequency.

5. The television tuner according to claim 3, wherein the first parallel tuned circuit has a first inductance element and a first capacitor connected in parallel with each other, the second parallel tuned circuit has a second inductance elementand a second capacitor connected in parallel with each other, the series tuned circuit has a second varactor diode, a third inductance element, and a third capacitor connected in series with each other, and a fourth capacitor connected in parallel withthe third capacitor through a second switch, when the television signal is received, a reverse bias voltage is applied to the first varactor diode and the second varactor diode, and the second switch is brought into an off state, when the FM broadcastsignal is received, a forward bias is applied to the first varactor diode and the second varactor diode, and the second switch is brought into an on state.

6. The television tuner according to claim 4, wherein the first parallel tuned circuit has a first inductance element and a first capacitor connected in parallel with each other, the second parallel tuned circuit has a second inductance elementand a second capacitor connected in parallel with each other, the series tuned circuit has a second varactor diode, a third inductance element, and a third capacitor connected in series with each other, and a fourth capacitor connected in parallel withthe third capacitor through a second switch, when the television signal is received, a reverse bias voltage is applied to the first varactor diode and the second varactor diode, and the second switch is brought into an off state, when the FM broadcastsignal is received, a forward bias is applied to the first varactor diode and the second varactor diode, and the second switch is brought into an on state.

7. The television tuner according to claim 1, wherein the intermediate-frequency tuned circuit is provided with a trap circuit, the trap circuit has an inductance element and a varactor diode connected in parallel with each other, when thetelevision signal is received, a reverse bias voltage is applied to the varactor diode, so that the trap circuit attenuates a signal of the frequency of the intermediate-frequency band corresponding to a voice carrier of a lower side television channeladjacent to a television channel to be received, when the FM broadcast signal is received, the reverse bias voltage applied to the varactor diode is lowered than when the television signal is received, and a trap frequency is a frequency between theimage carrier and the voice carrier of the intermediate-frequency band.

8. The television tuner according to claim 2, wherein the intermediate-frequency tuned circuit is provided with a trap circuit, the trap circuit has an inductance element and a second varactor diode connected in parallel with each other, whenthe television signal is received, a reverse bias voltage is applied to the second varactor diode, so that the trap circuit attenuates a signal of the frequency of the intermediate-frequency band corresponding to a voice carrier of a lower sidetelevision channel adjacent to a television channel to be received, when the FM broadcast signal is received, the reverse bias voltage applied to the second varactor diode is lowered than when the television signal is received, and a trap frequency is afrequency between the image carrier and the voice carrier of the intermediate-frequency band.

9. The television tuner according to claim 3, wherein the intermediate-frequency tuned circuit is provided with a trap circuit, the trap circuit has an inductance element and a second varactor diode connected in parallel with each other, whenthe television signal is received, a reverse bias voltage is applied to the second varactor diode, so that the trap circuit attenuatesa signal of the frequency of the intermediate-frequency band corresponding to the voice carrier of a lower sidetelevision channel adjacent to a television channel to be received, when the FM broadcast signal is received, the reverse bias voltage applied to the second varactor diode is lowered than when the television signal is received, and the trap frequency isa frequency between the image carrier and the voice carrier of the intermediate-frequency band.

10. The television tuner according to claim 4, wherein the intermediate-frequency tuned circuit is provided with a trap circuit, the trap circuit has an inductance element and a second varactor diode connected in parallel with each other, whenthe television signal is received, a reverse bias voltage is applied to the second varactor diode, so that the trap circuit attenuates a signal of the frequency of the intermediate-frequency band corresponding to a voice carrier of a lower sidetelevision channel adjacent to a television channel to be received, when the FM broadcast signal is received, the reverse bias voltage applied to the second varactor diode is lowered than when the television signal is received, and a trap frequency is afrequency between the image carrier and the voice carrier of the intermediate-frequency band.

11. The television tuner according to claim 5, wherein the intermediate-frequency tuned circuit is provided with a trap circuit, the trap circuit has a fourth inductance element and a third varactor diode connected in parallel with each other,when the television signal is received, a reverse bias voltage is applied to the third varactor diode, so that the trap circuit attenuates a signal of the frequency of the intermediate-frequency band corresponding to a voice carrier of a lower sidetelevision channel adjacent to a television channel to be received, when the FM broadcast signal is received, the reverse bias voltage applied to the third varactor diode is lowered than when the television signal is received, and a trap frequency is afrequency between the image carrier and the voice carrier of the intermediate-frequency band.

12. The television tuner according to claim 6, wherein the intermediate-frequency tuned circuit is provided with a trap circuit, the trap circuit has a fourth inductance element and a third varactor diode connected in parallel with each other,when the television signal is received, a reverse bias voltage is applied to the third varactor diode, so that the trap circuit attenuates a signal of the frequency of the intermediate-frequency band corresponding to a voice carrier of a lower sidetelevision channel adjacent to a television channel to be received, when the FM broadcast signal is received, the reverse bias voltage applied to the third varactor diode is lowered than when the television signal is received, and a trap frequency is afrequency between the image carrier and the voice carrier of the intermediate-frequency band.