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SDTV Reconstruction Filter with Adjustable Group Delay

SDTV Reconstruction Filter with Adjustable Group Delay

The MAX4450 operational amplifier configured in a 3-pole, low-pass Sallen-Key filter provides a Butterworth response with a bandwidth of 3dB at 5.25MHz. This circuit can be used for video anti aliasing and reconstruction filtering for composite (CVBS) or S-Video signals in standard definition digital TV (SDTV) applications. The circuit is designed to drive a 75Ω termination, common in video applications, with an overall gain of 1.



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This application note describes a 5.25MHz, 3-Pole, Butterworth filter using a Sallen-Key realization. It has gain of 2V/V, for driving a 75Ω back-terminated coax to an overall gain of 1. Such filters are used for video reconstruction of RGB and component video (Y, Pb, Pr) signals following a DAC to remove the higher frequency replicas of the signal, and as an anti-aliasing filter before an ADC.

 


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