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US 4,736,456 AGranted
Tuning system for television sets
AssigneeDeutsche Thomson-Brandt GmbH
InventorGerhard Maier
Life of this patent
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Abstract
An automatic alignment system for the tuner of a television receiver with a controlled high-frequency preamplifier stage and an intermediate-frequency amplifier that has a reference circuit with a resonance frequency that can be switched to the arithmetic mean between the video-carrier intermediate frequency and the audio-carrier intermediate frequency during automatic alignment. The maximum control voltage is employed as a criterion for optimum alignment and an auxiliary oscillator is switched on during automatic alignment and generates through a mixing stage an auxiliary frequency that corresponds to the arithmetic mean of the video-carrier frequency and the audio-carrier frequency from the tuner-oscillator frequency.
Claims2
Automatic alignment apparatus for a tuner of a television receiver comprising:
- high-frequency tuning circuits with capacity diodes;
- a controlled high-frequency preamplifier stage and an intermediate-frequency amplifier with a reference circuit having a resonance frequency;
- means for switching said resonance frequency to an arithmetic mean between a video-carrier intermediate frequency and an audio-carrier intermediate frequency during automatic alignment, maximum control voltage being a criterion for optimum alignment;
- an auxiliary oscillator switched on during automatic alignment;
- a tuner oscillator with a tuner-oscillator frequency;
- a mixing stage, said tuner oscillator generating an auxiliary frequency through said mixing stage corresponding to the arithmetic mean of a video-carrier frequency and an audio-carrier frequency from said tuner-oscillator frequency;
- digital-to-analog conversion means, tuning voltage being sequentially applied in digital steps through said digital-to-analog conversion means and said capacity diodes for automatic alignment, increase in tuning-voltage values being discontinued when a maximum control voltage is attained and a detected tuning-voltage value being retained in said digital-to-analog conversion means;
- a band filter with a high point in said tuning circuits, said mixing stage having an output connected downstream of said controlled high-frequency preamplifier stage to the high point of said band filter for automatic alignment of said band filter and simultaneous decontrol of said high-frequency preamplifier stage;
- said auxiliary oscillator being switched off when said preamplifier stage is controlled again and said tuner-oscillator frequency is increased half a difference frequency formed from said video-carrier intermediate frequency and said audio-carrier intermediate frequency;
- a preliminary filter circuit, increased tuning voltage produced during displacement of said tuner-oscillator frequency participating in alignment of said preliminary filter circuit so that an audio-carrier frequency of the channel to be received serves as an auxiliary frequency and said audio-carrier frequency is thereby aligned;
- means for switching thereafter said tuner-oscillator frequency back to a frequency intended for said tuner-oscillator by reduction in tuning voltage and simultaneously reducing thereby tuning voltage in said preliminary filter circuit by a same amount so that said preliminary filter circuit is tuned to the middle frequency of the channel to be received and said high-frequency band filter is switched back to correct alignment.
8 more elements
A method for automatically aligning a tuner of a television receiver comprising the steps of:
- providing high-frequency tuning circuits with capacity diodes and a controlled high-frequency preamplifier stage and an intermediate-frequency amplifier with a reference circuit having a resonance frequency;
- switching said resonance frequency to an arithmetic mean between a video-carrier intermediate frequency and an audio-carrier intermediate frequency during automatic alignment, maximum control voltage being a criterion for optimum alignment;
- switched on an auxiliary oscillator during automatic alignment;
- providing a tuner oscillator with a tuner-oscillator frequency;
- generating an auxiliary frequency with said tuner oscillator through a mixing stage corresponding to the arithmetic mean of a video-carrier frequency and an audio-carrier frequency from said tuner-oscillator frequency;
- applying tuning voltage sequentially in digital steps through digital-to-analog conversion means and said capacity diodes for automatic alignment, discontinuing increase in tuning-voltage values when a maximum control voltage is attained and retaining a detected tuning-voltage value in said digital-to-analog conversion means;
- providing a band filter with a high point in said high-frequency tuning circuits;
- transmitting an output of said mixing stage downstream of said controlled high-frequency preamplifier stage to the high point of said band filter for automatic alignment of said band filter, and decontrolling simultaneously said high-frequency preamplifier stage;
- switching off said auxiliary oscillator when said preamplifier stage is controlled again and increasing said tuner-oscillator frequency by half a difference frequency formed from said video-carrier intermediate frequency and said audio-carrier intermediate frequency;
- increased tuning voltage produced during displacement of said tuner-oscillator frequency participating in alignment of a preliminary filter circuit so that an audio-carrier frequency of the channel to be received serves as an auxiliary frequency and said audio-carrier frequency is thereby aligned;
- switching thereafter said tuner-oscillator frequency back to a frequency intended for said tuner-oscillator by reduction in tuning voltage and simultaneously reducing thereby tuning voltage in said preliminary filter circuit by a same amount so that said preliminary filter circuit is tuned to the middle frequency of the channel to be received, and switching back said high-frequency band filter to correct alignment.
8 more elements
Dependencies are inferred from the claim text.