High-Speed, Low-Distortion,

Differential Line Receivers

14

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TWISTED-PAIR-TO-COAX CABLE CONVERTER

Losses are higher at higher frequencies, contributing to

severe pulse-edge rounding in digital applications. The

nominal impedance of twisted-pair telephone wire is

110Ω.

The MAX4145/MAX4146, with variable gain up to

+10V/V and +100V/V, respectively, can be used to

compensate for cable losses. In the graph shown in

Figure 8, the cable characteristics are such that the

video-chroma frequency loss is almost 15dB greater

than the low-frequency loss. The losses can be com-

pensated for by using the RC-shaping network (Figure

9).

A 560Ω resistance and a 100pF capacitance shape the

MAX4146 gain to inversely match the frequency of the

1000 feet of telephone cable. The differential gain and

phase, using the circuit shown in Figure 9, is 0.55%

and 0.18°, respectively.

Figure 9. Circuit for Transmitting NTSC/PAL Video Over 1000 Feet of Twisted-Pair Telephone Line

VIDEO INPUT

VIDEO

OUTPUT

75

Ω

75

Ω

1, 7

8, 14

10

12

9

13

1000 FEET

2

6

MAX4147ESD

0.1

μF

0.1

μF

0.1

μF

11

9

13

75

Ω

2

110

Ω

560

Ω

100pF

6

5

3

MAX4146ESD

0.1

μF

1, 7

8, 14

OUT+

IN+

IN-

IN-

SENSE

IN+

OUT-

SENSE-

SENSE+

OUT

REF

75

Ω

75

Ω

COAX

75

Ω

MAX4147

MAX4144

__________________________________________________Typical Application Circuit