Switching voltage retrieval circuit - recovers enabling and disabling signal for colour channel in SECAM decoder and operates even in presence of noise

摘要

The retrieval circuit feeds the SECAM colour signal (a) to the SECAM decoder via a limiter stage (2) of a gate circuit (3). The signal at the gate circuit output is amplified, rectified and applied to the input of a threshold switch. A vertical sync. signal (b) is applied via a differentiator (85, 86) to one input of a bistable flip-flop comprising two NAND-gates (81, 84). An identification signal is applied via a second differentiator (82, 83) to the other input of the bistable flip-flop. The circuit operates reliably even in the presence of low signal-to-noise ratios.