MAX9541/MAX9542
Operating Modes
A/B controls whether Video Input A or Video Input B is
selected. See Table 1.
SHDN controls whether the device is on or off. See
Table 2. In shutdown, the outputs are in high imped-
ance.
Input
Each video source can provide up to four video signals.
Every video signal must be AC-coupled to the
MAX9541/MAX9542 through 0.1µF capacitors. The
MAX9541/MAX9542 have sync-tip clamps and bias cir-
cuits to restore the DC level of the video signal after the
input coupling capacitor. When a video input is select-
ed, the input has a sync-tip clamp, which accepts
video signals that have sync pulses or that reach their
minimum level during sync. Composite video with
blanking and sync (CVBS) is an example of a video sig-
nal with sync pulses. The red, green, and blue signals
in an RGBS signal set are examples of signals that
return to their blank level during sync. The sync-tip volt-
age is internally set to 300mV.
When a video input is not selected, the inputs to the
MAX9541/MAX9542 do not distort the video signal in
case the video source is driving video signals to anoth-
er video circuit such as a video multiplexer. The inputs
are biased at V
DD
/3, which is sufficiently above ground
so that the ESD diodes never forward bias as the video
signal changes. The input resistance is 220kΩ, which
presents negligible loading on the video current DAC.
The sole exception to this condition is IN3A, in which
the input circuit is always a sync-tip clamp. Table 3
summarizes which input circuit is active, dependent
upon A/B.
In shutdown mode (SHDN = LOW), a bias circuit is
active on every input.
Multiplexer
The MAX9541/MAX9542 have quadruple 2:1 multiplex-
ers to select between either Video Input A or Video
Input B as the source of the video signal. When A/B is
connected to GND, Video Input A is the video source.
When A/B is connected to V
DD
, Video Input B is the
video source.
Video Filter
The MAX9541 filter features ±1dB passband out to
9.5MHz and 47dB attenuation at 27MHz, making the fil-
ter suitable for standard-definition video signals from all
sources (e.g., broadcast and DVD). Broadcast video
signals are channel limited: NTSC signals have 4.2MHz
bandwidth, and PAL signals have 5MHz bandwidth.
Video signals from a DVD player, however, are not
channel limited; so the bandwidth of DVD video signals
can approach the Nyquist limit of 6.75MHz.
Recommendation: ITU-R BT.601-5 specifies 13.5MHz
as the sampling rate for standard-definition video.
Therefore, the maximum bandwidth of the signal is
6.75MHz. To ease the filtering requirements, most mod-
ern video systems oversample by two times, clocking
the video current DAC at 27MHz.
The MAX9542 does not have a filter.
Quadruple, 2:1, Mux Amplifiers for
Standard-Definition and VGA Signals
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