Schematic Reference

This part consists of a triple 6th order filter with selectable 33MHz or 8MHz frequencies. At any given time, the input signal’s DC levels must be between 0.0V and 1.3V to utilize the optimal headroom and to avoid clipping on the outputs. The 220 ?F capacitor coupled with the 150 ? termination forms a high pass filter that blocks the DC while passing the video frequencies and avoiding tilt. Lower values such as 10 ?F would create a problem. By AC coupling, the average DC level is zero. Thus, the output voltages of all channels will be centered around zero. Alternately, DC coupling the output of the FMS6418B is allowable. There are several trade-offs: The average DC level on the outputs will be 2V; each output will dissipate an additional 40mW nominally; The application will need to accommodate a 1V DC offset sync tip; And it is recommended to limit one 150 ? load per output.

The FMS6363 Low Cost Video Filter (LCVF) provides 6dB gain from input to  output. In addition, the input will be slightly offset to optimize the output driver performance. The FMS6363 provides an internal diode clamp to support AC-coupled input signals. If the input signal does not go below ground, the input clamp will not operate. This allows DAC outputs to directly drive the FMS6363 without and AC coupling capacitor (usually 220 ?F). The offset is held to the minimum required value to decrease the standing DC current into the load.