Buffer Output for Composite Output of AD725ARZ

I am using AD725ARZ to encode RGB signals to Composite Video.
As per datasheet in Interface Circuit Composite Output Pin Have a Series capacitor (220uF), what is the purpose of using Series capacitor. Is this capacitor Create any Problem to take Buffer output from Composite Output Pin.

  • 0
    •  Analog Employees 
    on Oct 21, 2020 11:38 AM 1 month ago

    Hi,

     Each output requires a 220 µF series capacitor to work with the 75 Ω resistance to pass low frequencies.
     For increased noise rejection, larger input capacitors are desired.

     Is this capacitor Create any Problem to take Buffer output from Composite Output Pin

        To provide a composite video output, the separate (S-Video)luminance and chrominance signal paths are summed.
    Prior to summing, however, a filter tap for removing cross-color artifacts in the receiver is provided.
       The luminance path contains a resistor, output pin (YTRAP),and buffer prior to entering the composite summer.
    By connecting an inductor and capacitor on this pin, an R-L-C series-resonant circuit can be tuned to null out the
    luminance frequency response at the chrominance subcarrier frequency (3.579 545 MHz for NTSC, 4.433 618 MHz for PAL).
        For more information please refer Composite Output section in AD725 datasheet.

    Note: AD725 outputs have a dc bias and must be ac coupled for proper operation.
    The COMP and LUMA outputs have information down to 30 Hz for NTSC (25 MHz for PAL) that must be trans-mitted.
    Each output requires a 220 μF series capacitor to work with the 75 Ω resistance to pass these low frequencies.
    The CRMA signal has information mostly up at the chroma frequency and can use a smaller capacitor if desired,
    but 220 μF can be used to minimize the number of different components used in the design.

    Thanks,

    Poornima