FMS6404: Precision Composite Video Output with Sound Trap and Group Delay Compensation

The FMS6404 is a single composite video 5th-order Butterworth low-pass video filter optimized for minimum overshoot and flat group delay. The device contains an audio trap that removes video information in a spectral location of the subsequent RF audio carrier. The group delay compensation circuit pre-distorts the signal to compensate for the inherent receiver intermediate frequency (IF) filter’s group delay distortion.In a typical application, the composite video from the DAC is AC coupled into the filter. The CV input has DC-restore circuitry to clamp the DC input levels during video synchronization. The clamp pulse is derived from the CV channel.All outputs are capable of driving 2VPP, AC- or DC-coupled, into either a single or dual video load. A single video load consists of a series 75Ω impedance matching resistor connected to a terminated 75Ω line. This presents a total of 150Ω of loading to the part. A dual load would be two of these in parallel, which presents a total of 75Ω to the part. The gain of the CV signal is 6dB with 1VPP input levels. All video channels are clamped during synchronization to establish the appropriate output voltage reference levels.

Features

• 7.6MHz 5th-Order Composite Video Filter
• 14dB Notch at 4.425MHz to 4.6MHz for Sound Trap Capable of Handling Stereo
• 50dB Stopband Attenuation at 27MHz on CV Output
• >0.5dB Flatness to 4.2MHz on CV Output
• Equalizer and Notch Filter for Driving RF Modulator with Group Delay of -180ns
• No External Frequency Selection Components or Clocks
• <5ns Group Delay on CV Output
• AC-Coupled Input
• AC- or DC-Coupled Output
• Capable of PAL Frequency for CV
• Continuous Time Low-Pass Filters
• <1.4% Differential Gain with 0.7° Differential Phase on CV Channel
• Integrated DC Restore Circuitry with Low Tilt