Analog video filter ICs tame HD aliases

SUNNYVALE, Calif–Digital video still needs those analog filters, and the Maxim MAX9500 and MAX9501 provide key filtering functions for the high-definition video signal path. These triple-channel filters offer better than 50 dB of attenuation at 44.25 MHz, needed for HD signals sampled at 74.25 MHz. Designers can use these ICs for antialiasing filters on analog inputs, as well as reconstruction filters for video outputs.

The large amount of out-of-band attenuation is needed because HD video signals, with their 30-MHz bandwidth, are sampled or reconstructed at 74.25 MHz, yielding an alias spectral component at 44.25 MHz. As a result, the requisite filter must have 30 MHz baseband passband, but rolloff sharply after that point, and fully attenuate the alias. The vendor claims that competitive filters can provide only 15 dB attenuation at 44.25 MHz (Figure) in contrast to these filters, which provide at least 40 dB attenuation at 74.25 MHz and meet EIA-770.3 and SMPTE274M response requirements, (Figure) . In addition, the three channels have closely matched group delay and gain characteristics.

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Figure 1: Attenuation of Maxim MAX9500 versus competitive device

The MAX9500 (+5V supply) and MAX9501 (±5V supply) can drive two loads at the same time, for applications such as set-top boxes where users have a pair of high-definition component outputs (Y/Pr/Pb) such as TV and recorder; users will no longer need to purchase two sets of drivers. Outputs can drive single or double back-terminated loads (150Ω or 75Ω), and sink and source output current; the internal gain of 6 dB means the devices can drive 75Ω back-terminated loads with overall gain of +1. Inputs are DC-coupled to eliminate sync crush, droop, and field tilt, while outputs can be DC- or AC-coupled. The dual-supply version meets the needs of designers who already have dual supplies and do not want to AC-couple the outputs, which adds capacitor cost and degrades the video signal.

The MAX9500 and MAX9501, available in 5 x 6 mm, 16-pin QSOP and 16-pin SO packages, are $1.05 (1000 pieces). For the data sheet, click on:

Maxim Integrated Products, 1-800-998-8800,

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