Integrating sound notch and eliminateing discrete devices

Fairchild Semiconductor says its FMS6406 is the industry’s most highly integrated standard definition, low-pass reconstruction video filter/driver. This device features an integrated sound notch and output drivers that meet the latest cable and satellite set-top box performance requirements of 170ns group delay predistortion.

The FMS6406 compensates for the inherent distortion in the TV receiver by including a group delay and chroma-luma delay FCC predistortion circuit. This prevents the image’s high-frequency edges from appearing distorted on the TV screen. The notch filter creates a window in the video signal at approximately 4.5MHz to stop interference between the audio and video before these signals are combined in the channel 3/4 RF modulator.

Fairchild’s FMS6406, a fifth order video filter, gets rid of unwanted digital artefacts by significantly reducing the clock and image frequencies after the digital-to-analogue conversion process occurs on an MPEG chip. This video filter/driver is also capable of DC coupling on the outputs to improve the low-frequency video, at the same time dispensing with the usual three large capacitors.

Typical designs for set-top boxes offer both S-video and composite-video outputs. Fairchild’s FMS6406 offers separate chrominance and luminance outputs to directly drive the S-video output. These outputs are also internally summed to form a composite video signal. The composite- and S-video outputs provide a fixed gain of 6 dB and offer the flexibility of either AC or DC coupling.

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