MAX11506/MAX11507
Low-Cost, 6-Channel SD Plus HD/SD
Selectable Video Filters and Buffers
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AC-Coupled Inputs
When 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 CVBS, 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. Figure 4
shows a typical network. Determine the bias voltage using:
where I
L
is the input leakage current (typically 0.5µA).
SD Filters
The MAX11506/MAX11507 filters are optimized to deliv-
er a flat (MAX11506) or high-frequency boosted
(MAX11507) passband and high stopband attenuation.
The filter characteristic provides excellent time domain
response with low overshoot. The typical -3dB frequen-
cy of 9.0MHz guarantee minimal attenuation in the
passband, while at the same time offering a 27MHz
attenuation of typically -48dB.
HD Filters
The internal filters deliver a flat passband along with high
stopband attenuation. The filter characteristic provides
an excellent time domain response with low overshoot.
The typical -3dB frequency of 33MHz guarantees low
attenuation in the passband, while at the same time
allowing for a typical attenuation of -46dB at 74.25MHz.
Output Buffers
The MAX11506/MAX11507 feature output buffers with
+6dB gain that drive a standard 150Ω video load. A
typical load consists of a 75Ω backmatch resistor, an
optional 220µF or larger coupling capacitor, and a 75Ω
termination resistor. The offset between input and out-
put signals ensures that the blanking level on the output
is less than 1V after the backmatch resistor, thus meet-
ing digital TV specifications allowing the devices to
drive video loads directly without using costly AC-coupling
capacitors.
Applications Information
Output Considerations
The MAX11506/MAX11507 outputs may be DC- or AC-
coupled. These devices, with +6dB gain, are typically
connected to a 75Ω series backmatch resistor followed
by the video cable. Choose an AC-coupling capacitor
value that ensures that the lowest frequency content in
the video signal is passed and the field-time distortion
is kept within desired limits when using an AC connec-
tion. The selection of this value is a function of the input
impedance, and more importantly, the input leakage of
the circuit being driven. Common industry practice is to
use a 220µF or larger capacitor.
