Encoding circuit for a secam color television transmitter
AssigneeU.S. Philips Corporation
InventorNicolaas J. L. Van der Valk
Life of this patent
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Abstract
An encoding circuit for a SECAM color television transmitter having a frequency modulator circuit for a modulating signal which comprises two color difference signals which follow one another line-sequentially and are controlled by means of two phase control loops and two reference signal generators. A first reference signal generator has one of the reference frequencies whereas the frequency of the signal generated by the second reference signal generator is a harmonic of the line frequency. The phase control loop to which the second reference signal generator is connected comprises a sample and hold circuit which is operative at field frequency.
Claims13
An encoding circuit for a SECAM colour television transmitter comprising:
- a pulse generator for generating a line signal frequency and a field signal frequency, a frequency modulator circuit switchably connected to said pulse generator and comprising a frequency-modulatable oscillator for converting a modulating signal containing two color difference signals which follow one another line-sequentially each color difference signal having a direct current component added thereto, into a frequency-modulated signal having a first reference frequency at a first value of the first colour difference signal and a second reference frequency at a second value of the second colour difference signal,
- a first phase control loop connected to said frequency modulator circuit for generating a first control voltage for said frequency modulator circuit and including a first sample and hold circuit, said first sample and hold circuit being operative in a time interval in which said first color difference signal has said first value,
- a first reference signal generator connected to said first phase control loop for generating a signal having the first reference frequency, and
- further comprising a second phase control loop connected to said frequency modulator circuit for generating a second control voltage for said frequency modulator circuit and including a second sample and hold circuit, said second sample and hold circuit being operative at field frequency and in a time interval in which said second color difference signal has said second value,
- a second reference signal generator being connected to said second phase control loop, so that the frequency of the signal generated by said second reference signal generator is a harmonic of the line frequency and so that the second sample and hold circuit is operative during a period of time which is long relative to one period of the signal generated by said second reference signal generator.
Dependencies are inferred from the claim text.