MAX9500/MAX9501
Triple-Channel HDTV Filters
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Detailed Description
The MAX9500/MAX9501 are fully integrated solutions
for filtering and buffering HDTV signals. The MAX9500
operates from a single +5V supply, while the MAX9501
operates from dual ±5V supplies. The MAX9500/
MAX9501 interface between the current-output DACs of
an ATSC, MPEG decoder, and the external connections
of a television, set-top box, or DVD player. The
MAX9500/MAX9501 feature a DC-coupled input buffer
with very low input capacitance, highly selective lowpass filters to remove out-of-band noise, and a gain of
+6dB in the output amplifier to drive 75Ω back-termi-
nated loads to unity gain. The DC-coupled input buffer
eliminates sync crush, droop, and field tilt. The output
load can be DC- or AC-coupled.
Filter
The MAX9500/MAX9501 reconstruction filters feature a
6th-order elliptical response, providing a 1.5dB flat
passband response up to 30MHz. The filter meets the
selectivity requirements of the EIA-770.3/SMPTE 274M
filtering template, achieving > 40dB attenuation at
44.25MHz. The MAX9500/MAX9501 can also be used
as anti-aliasing filters for HDTV component inputs.
Output Buffer
The MAX9500/MAX9501 output buffers provide +6dB of
gain and can drive 2V
P-P
into a single or double back-terminated load (150Ω or 75Ω, respectively) directly to
ground. The output can be AC-coupled or DC-coupled.
Applications Information
Input Considerations
The MAX9500/MAX9501 inputs are normally DC-coupled. No AC-coupling capacitors are required because
the input voltage range includes ground and extends
up to 1.4V, allowing the MAX9500/MAX9501 to be
directly connected to the output of a single-supply, current-output DAC without any external bias network.
The MAX9500/MAX9501 inputs can be AC-coupled.
Use a fixed bias or video clamp to set the DC bias to
ensure that the negative peak of the video signal is as
near to 0V as possible. A video clamp is preferred
because it limits the total swing of the signal and holds
the blanking level constant.
Output Considerations
The MAX9500/MAX9501 outputs are normally DC-coupled, so no AC-coupling capacitors are required. For 0V
input, the MAX9500 output voltage is 0.8V and the
MAX9501 output voltage is 0V, typical. Connect the
MAX9500/MAX9501 directly to a video cable with a 75Ω
series back-termination resistor to match the impedance
of the cable. Properly terminate the other end of the
cable with a 75Ω load. The MAX9500/MAX9501 outputs
can sink and source current allowing the device to be
AC-coupled. However, AC-coupling the outputs will
degrade the tilt.
Power-Supply Bypassing and Layout
Considerations
The MAX9500 operates from a single +5V supply while
the MAX9501 operates from dual ±5V supplies. Bypass
VCCand VEE(MAX9501) to GND with a 0.1µF capacitor
as close to the device as possible, and an additional
1µF capacitor in parallel if any significant low-frequency
disturbances are present in the vicinity of the
MAX9500/MAX9501. Use an extensive ground plane to
ensure optimum performance.
The input and output termination resistors should be
placed as close to the device as possible to avoid performance degradation in the frequency response.
The PC board traces at the output should have 75Ω
characteristic impedance when matching into a 75Ω
characteristic impedance cable. Keep the board trace
at the inputs and outputs of the MAX9500/MAX9501 as
short as possible to minimize the parasitic stray capacitance and noise pickup.
Pin Description