FM Television signal receiving circuit

• US 4,417,279 A
• Filed: 02/11/1982
• Issued: 11/22/1983
• Est. Priority Date: 02/16/1981
• Status: Expired due to Term

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Noda, Masaki, Shinkawa, Keiro, Matsuura, Shigeo, Sodeyama, Chuichi, Kondo, Masakazu
• Primary Examiner(s): Murray, Richard
• Application Number:
  US06/348,016
• Time in Patent Office: 649 Days
• Field of Search: 358/188, 358/191.1, 358/195.1, 455/182, 455/184, 455/192, 455/205, 455/208, 455/255, 455/257, 455/265
• US Class Current: 348/735
• CPC Class Codes: H04N 5/50 Tuning indicators; Automatic tuning control

Abstract

A receiving circuit for a television receiver for receiving an FM-modulated television signal is disclosed, in which the oscillation frequency of a local oscillator circuit is fine adjusted by a voltage of a sync signal of the FM-modulated television signal thereby to receive the television signal properly.

Claims

1. A receiving circuit for a television receiver for receiving an FM-modulated television signal, comprising:

a mixer circuit, supplied with an FM-modulated television signal of a first frequency band and a local oscillation signal from a local oscillator circuit, for converting said FM-modulated television signal of the first frequency band into a television signal of a second frequency band in accordance with said local oscillation signal;

the local oscillator circuit generating the local oscillation signal and applying it to said mixer circuit, a frequency of the local oscillation signal being varied in accordance with a tuning voltage supplied from an external source which represents a channel of the television signal to be received;

an FM detector circuit for FM-detecting the FM-modulated television signal of the second frequency band from said mixer circuit and producing a television composite video signal;

a video amplifier circuit for amplifying the composite video signal from said FM detector circuit;

a sync separation circuit for separating a sync signal from the composite video signal applied thereto from said video amplifier circuit and outputting only said sync signal;

a sampling circuit, supplied with the composite video signal from said FM detector circuit and the sync signal from said sync separation circuit, for picking up the sync signal voltage of said composite video signal in accordance with said sync signal from said sync separation circuit, said sampling circuit producing an output voltage corresponding to the frequency spectrum of the sync signal of the television signal of the second frequency band, and applying it to a hold circuit; and

the hold circuit for holding the output voltage signal from said sampling circuit for a predetermined period, producing a DC voltage corresponding to the output voltage signal from said sampling circuit, and applying said DC voltage to said local oscillator circuit, said DC voltage being superimposed on the tuning voltage applied to said local oscillator circuit and controlling the oscillation frequency of said local oscillator circuit such that the frequency spectrum of the sync signal of the television signal of the second frequency band takes a predetermined value.

2. A receiving circuit for a television receiver for receiving an FM-modulated television signal, comprising:

a first mixer circuit, supplied with an FM-modulated television signal of SHF band from an antenna and a first local oscillation signal from a first local oscillator circuit, for converting said FM-modulated television signal of SHF band into an FM-modulated television signal of UHF band in accordance with said first local oscillation signal;

the first local oscillator circuit for producing the first local oscillation signal of a predetermined frequency and applying said first local oscillation signal to said first mixer circuit;

an amplifier for power-amplifying the FM-modulated television signal of UHF band supplied thereto from said first mixer circuit and applying the power-amplified FM-modulated television signal to a second mixer circuit;

the second mixer circuit, supplied with the FM-modulated television signal from said amplifier and a second local oscillation signal from a second local oscillator circuit, for converting said FM-modulated television signal of UHF band into an FM-modulated television signal of VHF band in accordance with said second local oscillation signal;

the second local oscillator circuit for generating the second local oscillation signal and applying it to said second mixer circuit, a frequency of the second oscillation signal being varied in accordance with a tuning voltage applied from an external source which represents a channel of the television signal to be received;

an FM detector circuit for FM-detecting the FM-modulated television signal of VHF band supplied thereto from said second mixer circuit and producing a television composite video signal;

a video amplifier circuit for amplifying the composite video signal applied thereto from said FM detector circuit;

a sync separation circuit for separating a sync signal from the composite video signal applied thereto from said video amplifier circuit and outputting only said sync signal;

a sampling circuit, supplied with the composite video signal from said FM detector circuit and the sync signal from said sync separation circuit, for picking up the sync signal voltage of said composite video signal in accordance with said sync signal from said sync separation circuit, said sampling circuit producing an output voltage corresponding to the frequency spectrum of the sync signal of the television signal of VHF band and applying it to a hold circuit; and

the hold circuit for holding the output voltage signal from said sampling circuit for a predetermined period, generating a DC voltage corresponding to the output voltage signal from said sampling circuit, and applying said DC voltage to the second local oscillator circuit, said DC voltage being superimposed on the tuning voltage applied to said second local oscillator circuit and controlling the oscillation frequency of said second local oscillator circuit such that the frequency spectrum of the sync signal of the television signal of VHF band takes a predetermined value.

3. A receiving circuit for a television receiver for receiving an FM-modulated television signal, conprising:

a first mixer circuit, supplied with an FM-modulated television signal of SHF band from an antenna and a first local oscillation signal from a first local oscillator circuit, for converting said FM-modulated television signal of SHF band into an FM-modulated television signal of UHF band in accordance with said first local oscillation signal;

the first local oscillator circuit for producing the first local oscillation signal of a predetermined frequency and applying said first local oscillation signal to said first mixer circuit;

an amplifier for power-amplifying the FM-modulated television signal of UHF band supplied thereto from said first mixer circuit and applying the power-amplified FM-modulated television signal to a second mixer circuit;

the second mixer circuit, supplied with the FM-modulated television signal from said amplifier and a second local oscillation signal from a second local oscillator circuit, for converting said FM-modulated television signal of UHF band into an FM-modulated television signal of VHF band in accordance with said second local oscillation signal;

the second local oscillator circuit for generating the second local oscillation signal and applying it to said second mixer circuit, a frequency of the second oscillation signal being varied in accordance with a tuning voltage applied from an external source which represents a channel of the television signal to be received;

a limiter circuit for removing a signal with an amplitude larger than a predetermined level from the FM-modulated television signal of VHF band applied thereto from said second mixer circuit in order to remove AM noises therefrom, and then applying the FM-modulated television signal of VHF band to an FM detector circuit;

the FM detector circuit for FM detecting the television signal of VHF band applied from said limiter circuit, thus producing a television composite video signal;

a video amplifier circuit for amplifying the composite video signal applied thereto from said FM detector circuit;

a sync separation circuit for separating only a sync signal from the composite video signal applied thereto from said video amplifier circuit and outputting only said sync signal;

a sampling circuit, supplied with the composite video signal from said FM detector circuit and the sync signal from said sync separation circuit, for picking up the sync signal voltage of said composite video signal in accordance with said sync signal from said sync separation circuit, said sampling circuit producing an output voltage corresponding to the frequency spectrum of the sync signal of the television signal of VHF band and applying it to a hold circuit; and

the hold circuit for holding the output voltage signal from said sampling circuit for a predetermined period, producing a DC voltage corresponding to the output voltage signal from said sampling circuit, and applying said DC voltage to said second local oscillator circuit, said DC voltage being superimposed on the tuning voltage applied to said second local oscillator circuit and controlling the oscillation frequency of said second local oscillator circuit such that the frequency spectrum of the sync signal of the television signal of VHF band takes a predetermined value.

4. A receiving circuit according to claim 3, wherein said limiter circuit includes a band-pass filter with a narrow pass band.