Rainbow Electronics MAX7439 - Manual (Page 6)

MAX7438/MAX7439
Detailed Description
Filter
Filter Response
The MAX7438/MAX7439 reconstruction filters consist of
three separate lowpass filters with Butterworth-type
response. The filter features a maximally flat passband
for NTSC and PAL bandwidths, while maintaining good
group delay characteristics. The stopband offers excel-
lent attenuation at frequencies of 27MHz and above
(see the Typical Operating Characteristics section).
The autotrimming circuit digitally controls the corner fre-
quency to maintain the frequency characteristics over
process and temperature.
High-Frequency Boost
The high-frequency boost compensates for signal
degradation and roll-off in the signal path prior to the
MAX7438/MAX7439 to increase image sharpness.
Program the level of high-frequency boost for each
channel by selecting the corresponding external resis-
tor values (R
HFB_-1 and R HFB_-2 , as shown in the
Typical Operating Circuit section) given in Table 1. The
Triple-Channel Video Reconstruction Filters with
Back-Porch Clamp to GND
6 _______________________________________________________________________________________
Pin Description
PIN NAME FUNCTION
1, 4, 7, 10,
11, 13, 15, 19
GND Ground
2 IN1 Channel 1 Video Input
3 HFB1
Channel 1 High-Frequency Boost and Filter Bypass Control Input. Connect external resistors to HFB1
for high-frequency boost and filter bypass control. See Table 1.
5 OUT1 Channel 1 Video Output
6 V
CC
+5V Power Input
8 OUT2 Channel 2 Video Output
9 V SS -5V Power Input. Connect the backside exposed pad to V SS .
12 OUT3 Channel 3 Video Output
14 HFB3
Channel 3 High-Frequency Boost and Filter Bypass Control Input. Connect external resistors to HFB3
for high-frequency boost and filter bypass control. See Table 1.
16 IN3 Channel 3 Video Input
17 HFB2
Channel 2 High-Frequency Boost and Filter Bypass Control Input. Connect external resistors to HFB2
for high-frequency boost and filter bypass control. See Table 1.
18 IN2 Channel 2 Video Input
20 EXT External Bias Resistor. Connect a 10k Ω resistor from EXT to GND.
— EP Exposed Paddle. Connect to V SS . Do not connect to GND.
MODE
R HFB_-1
(k Ω)
R HFB_-2
(k Ω)
V HFB_ (V)
(V
CC
= 5V)
NOMINAL BOOST (dB)/
BYPASS
(MAX7438)
NOMINAL BOOST (dB)/
BYPASS
(MAX7439)
Bypass Open 0 0 Bypass Bypass
No boost 15 1 0.318 0 0
Boost 1 11.3 2 0.758 0.5 0.75
Boost 2 16.5 7.32 1.53 1.0 1.5
Boost 3 11.3 11.3 2.5 1.5 2.25
Boost 4 4.42 18.2 4.027 2.0 3.0
Table 1. External Resistor Values for Bypass Mode and High-Frequency Boost Control