High-Speed, Low-Distortion,

Differential Line Receivers

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13

which appears inductive at high frequencies. This

inductance forms an L-C resonant circuit with the

capacitive load, which causes peaking in the frequency

response and degrades the amplifier’s phase margin.

The MAX4144/MAX4145/MAX4146 drive capacitive

loads up to 25pF without oscillation. However, some

peaking may occur in the frequency domain (Figure 4).

To drive larger capacitance and reduce ringing, add an

and the load (Figure 5).

capacitive load (Figures 6 and 7). With higher capaci-

tive values, bandwidth is dominated by the RC network

itself is much higher. Also note that the isolation resistor

forms a divider that decreases the voltage delivered to

the load.

Twisted-Pair Line Receiver

The MAX4144/MAX4145/MAX4146 are well suited as

receivers in twisted-pair xDSL or NTSC/PAL video

applications. The standard 24AWG telephone wire

widely used in these applications is a lossy medium for

high-frequency signals. The losses in NTSC video

applications are almost 15dB per 1000 feet (Figure 8).

4

0

8

6

CAPACITIVE LOAD (pF)

200

16

18

12

10

14

50

150

250

20

100

Figure 6. MAX4144 Isolation Resistance vs. Capacitve Load

0

0

5

CAPACITIVE LOAD (pF)

200

25

15

10

20

50

150

250

30

100

Figure 7. MAX4145/MAX4146 Isolation Resistance vs.

Capacitive Load

OUT

MAX4144

MAX4145

MAX4146

15

-35

-30

-25

10k

1M

10M

-20

-15

-10

-5

0

5

10

100k

FREQUENCY (Hz)

Figure 8. 1000 Feet of AWG24 Twisted-Pair Telephone Cable

(Gain vs. Frequency)