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-

Typical Operating Circuit section) given in Table 1. The

Triple-Channel Video Reconstruction Filters with

Back-Porch Clamp to GND

6

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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

+5V Power Input

8

OUT2

Channel 2 Video Output

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

MODE

(k

Ω)

(k

Ω)

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