Precision S-Video Filter with Summed Composite Output, Sound Trap and Group Delay Compensation

The FMS6406 is a dual Y/C 5th-order Butterworth lowpass video filter optimized for minimum overshoot and flat group delay. The device also contains a summing circuit to generate filtered composite video, an audio trap and group delay compensation circuit. The audio trap removes video information in the spectral location of the subsequent RF audio carrier. The group delay circuit predistorts the signal to compensate for the inherent receiver IF filter’s group delay distortion.In a typical application, the Y and C input signals from DACs are AC-coupled into the filters. Both channels have DC-restore circuitry to clamp the DC-input levels during video sync. The Y and C channels use separate feedback clamps. The clamp pulse is derived from the Y channel. All outputs are capable of driving 2 Vpp, AC or DC-coupled, into either a single or dual video load. A single video load consists of a series 75 ohm impedance matching resistor connected to a terminated 75 ohm line, this presents a total of 150 ohm of loading to the part. A dual load would be two of these in parallel which would present a total of 75 ohm to the part. The gain of the Y, C and CV signals is 6dB with 1 Vpp input levels. All video channels are clamped during sync to establish the appropriate output voltage reference levels.