Out in Front: December 21, 1995

Before digitizing a video signal or after reconstructing one using a D/A converter, the signal must pass through a lowpass filter to eliminate aliasing and artifacts. This task requires building a filter—or triple filter for RGB or noncomposite video—using a video-bandwidth op amp and discrete components. Micro Linear’s ML6420 avoids this problem by integrating the op amps and requisite auxiliary components in a monolithic device.

This triple lowpass video filter in a 16-pin SOIC package implements a sixth-order phase-equalized filter design. Depending on the specific version, it provides cutoff frequency combinations from a menu of 5.50-, 9.34-, 3.34-, or 1.67-MHz values, matched to RGB, YUV, S-video, or composite-video requirements. A range-control pin lets you change the input-span offset by 0.5V, so that the filter can accommodate inputs from 0 to 1V or 0 to 2V, and the IC provides a 1V p-p output into a 75 ohm load (0.5 to 1.5V) or 2V p-p into 150 ohm (0.5 to 2.5V).

Stopband rejection is greater than 45 dB, and differential phase and gain errors are less than 2% and 2×, respectively. The ML6420 uses a 5V supply, requires no external components or clock, and costs $4.95 (10,000). The similar ML6421 ($5.25) also includes (sin x)/x frequency equalizers for each channel to overcome the amplitude falloff that occurs at the output of some D/A converters in reconstructed video applications. -- by Bill Schweber

Micro Linear Corp, San Jose, CA. (408) 433-5200.