Rainbow Electronics MAX9501 - Manual (Page 7)

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 low-
pass filters to remove out-of-band noise, and a gain of
+6dB in the output amplifier to drive 75
Ω 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-ter-
minated load (150 Ω 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-cou-
pled. 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, cur-
rent-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-cou-
pled, 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 75
Ω
series back-termination resistor to match the impedance
of the cable. Properly terminate the other end of the
cable with a 75
Ω 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
V
CC and V EE (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 per-
formance degradation in the frequency response.
The PC board traces at the output should have 75
Ω
characteristic impedance when matching into a 75
Ω
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 capaci-
tance and noise pickup.
Pin Description
PIN
MAX9500 MAX9501
NAME FUNCTION
1, 7, 8,
9, 16
— SUBG
Substrate Ground. Connect
to ground.
2 2 YIN Y Channel Input
3, 5 3, 5 GND Ground
4 4 PbIN Pb Channel Input
6 6 PrIN Pr Channel Input
10 10 PrOUT Pr Channel Output
11, 13, 15 11, 13, 15 V CC Positive Supply
12 12 PbOUT Pb Channel Output
14 14 YOUT Y Channel Output
—
1, 7, 8,
9, 16
V EE Negative Supply