MAX11501/MAX11502
Three-Channel,
Standard-Definition Video Filters
6 _______________________________________________________________________________________
Input Coupling
The choice of AC- or DC-coupling the input depends
on the video source. Many DACs provide a current out-
put and are terminated to ground with a resistor. Such
DAC outputs are conveniently DC-coupled to the
MAX11501/MAX11502. Use AC-coupling when the DC
level of the video signal is unknown or outside the
specified input range of the MAX11501/MAX11502,
such as SCART or V
CC
terminated DAC outputs.
DC-Coupled Inputs
If the input is DC-coupled, the input voltage must
remain above zero but not exceed the maximum input
voltage of 1.4V (typical).
AC-Coupled Inputs
If the input is AC-coupled, the transparent clamps are
active and set the lowest point of the signal at ground.
This is appropriate for unipolar signals such as Y, R, G,
or B, with or without sync pulses (Figure 3).
For bipolar signals such as Pb and Pr, bias the AC-cou-
pled inputs to a fixed DC voltage, typically 0.59V, to ensure
that the transparent clamp remains off. A suitable network
is shown in Figure 4. Determine the bias voltage using:
where I
L
is the input leakage current (typically 0.5µA).
