Colour reference control for SECAM system TV receivers - uses DC levels derived from sampled and stored signals via common potentiometer

摘要

The control system is for TV receivers using the SECAM colour system. The circuit allows correct measurement of the frequency excursion of the colour signals from the two sub-carrier reference or 'black' levels. A signal generated in response to a stable reference frequency is sampled and stored and provides a DC level as a function of this reference. The two DC levels associated with each sub-carrier colour signal are injected downstream of the demodulators during the line or frame flyback time. The DC levels are derived from the store via a common potentiometer.