Reconstruction Video Filter Using the ADA4430-1 Amplifier After the ADV7393 Video Encoder (cn0101)
This circuit illustrates a digital-to-analog video converter paired with a low cost, low power, fully integrated reconstruction video filter. Although many video encoders (video DACs) such as the ADV7393 can drive a video load directly, it is often very beneficial to use a video driver at the output of a video encoder for power savings, line driving, and additional circuit protection. The video driver is typically configured as an active filter, also known as a reconstruction or anti-imaging filter. The purpose of the reconstruction filter is twofold: it blocks the higher frequency components (above the Nyquist frequency) that were introduced into the video signal as part of the digitization process and provides gain to drive the external 75 Ω cable to the video display. For ac-coupled output applications, the ADA4430-1 has an integrated SAG correction network. Signal amplitude gain (SAG) correction is used to provide low frequency compensation for the high-pass filter formed by the 150 Ω video load of a back-terminated cable and the output coupling capacitor. SAG correction reduces the size of the traditionally large ac coupling capacitor (330 μF), replacing it with much smaller 47 μF and 22 μF capacitors.
The ADA4430-1 and the ADV7393 are both recommended for automotive application, which makes both products ideal for infotainment and vision-based safety systems applications.
Figure 1: Low Cost, Fully Integrated Reconstruction Filter using the ADA4430-1(Simplified Schematic)
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