Video Reconstruction Filters Include Back Porch Clamp June 2003 Issue Published Date: June 01, 2003
The MAX7438 and MAX7439 enter the market as the first three-channel video reconstruction filters to include a back-porch clamp that sets the blanking level of the video signal to ground on the output. This maintains the video output dc level to 0V regardless of the input and is said to eliminate the need for large output ac coupling capacitors. Each channel includes a lowpass filter with adjustable boost levels and an adjustable gain amplifier capable of driving two 150ž loads. The MAX7438 has a buffer gain of 2V/V while the MAX7439 has a buffer gain of 3V/V. Each filter channel achieves 60 dB of attenuation at 27 MHz with less than ±0.25 dB of passband ripple from dc to 5.5 MHz. High-frequency boost circuitry allows adjustment for sharper images with up to 2 dB of gain boost in 0.5 dB increments without degradation in stopband attenuation. Both devices are available in a 20-pin QFN package, with prices starting at $2.20 each/1,000. MAXIM INTEGRATED PRODUCTS, Sunnyvale, CA. (800) 998-8800.
