Triple-Channel Video Reconstruction Filter and

Buffer for Composite and Y/C Outputs

4

_______________________________________________________________________________________

65

70

80

75

85

90

-40

10

-15

35

60

85

SUPPLY CURRENT

vs. TEMPERATURE

TEMPERATURE (

°C)

DIFFERENTIAL GAIN

13

24

5

6

7

13

24

5

6

7

0.2

0.3

0.1

0

-0.1

-0.2

-0.3

0.2

0.3

0.1

0

-0.1

-0.2

-0.3

DIFFERENTIAL PHASE

MULTIBURST RESPONSE

YIN

200mV/div

YOUT

200mV/div

10

µs/div

Typical Operating Characteristics (continued)

Detailed Description

The primary function of the MAX7443/MAX7444 is to fil-

ter and buffer the encoder DAC outputs that contain

digital video information in applications such as set-top

boxes, hard-disk recorders, DVD players, and digital

VCRs. These devices reconstruct and clean up analog

video signals. Each MAX7443/MAX7444 consists of a

lowpass filter and an adjustable-gain output video

buffer that is capable of driving two standard 150

Ω

video loads. The luma (YIN) and chroma (CIN) video

inputs are summed internally to provide the composite

(CVOUT) video output.

These devices operate from a single +5V supply. The

filters have a nominal cutoff frequency optimized for

NTSC, PAL, and SDTV.

Filter

Filter Response

The reconstruction filter consists of two 2nd-order

Sallen-Key stages. The Butterworth-type response fea-

tures a maximally flat passband for NTSC and PAL

bandwidths. The stopband offers 41dB (typ) of attenua-

tion at sampling frequencies of 27MHz and above (see

Typical Operating Characteristics).

High-Frequency Boost

The high-frequency boost available in the MAX7444

compensates for signal degradation and rolloff in the

video encoder, which increases the image sharpness.

The MAX7443 has a flat response over the video band-

width.

Output Buffer

The output buffer drives two 150

Ω video loads with a

provides a gain of 6dB, 9.5dB, and 12dB, which are

ing, respectively. The MAX7443/MAX7444 can drive an

AC load or drive the video load directly without using

the large output capacitor. The output buffer drives a

DC load with an output blanking level of less than 1V.

PIN

NAME

FUNCTION

1

YIN

Luma (Y) Input

2

GSET

Gain-Setting Control Input. See Table 1

for values.

3

CIN

Chroma (C) Input

4

GND

Ground

5V Power Supply

6

COUT

Chroma (C) Output

7

CVOUT

Composite Video Output

8

YOUT

Luma (Y) Output

Pin Description