LT1714IGN datasheet(11/16 Pages) LINER

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LT1713/LT1714

TYPICAL APPLICATIO S

Simultaneous Full Duplex 75Mbaud Interface

with Only Two Wires

The circuit of Figure 3 shows a simple, fully bidirectional,

differential 2-wire interface that gives good results to

75Mbaud, using the LT1714. Eye diagrams under condi-

tions of unidirectional and bidirectional communication

are shown in Figures 4 and 5. Although not as pristine as

the unidirectional performance of Figure 4, the perfor-

mance under simultaneous bidirectional operation is still

excellent. Because the LT1714 input voltage range ex-

tends 100mV beyond both supply rails, the circuit works

with a full

±3V (one whole VS up or down) of ground

potential difference.

The circuit works well with the resistor values shown, but

other sets of values can be used. The starting point is the

characteristic impedance, ZO, of the twisted-pair cable.

The input impedance of the resistive network should

match the characteristic impedance and is given by:

[]

••

||(

)

•||(

)

This comes out to 120

Ω for the values shown. The

Thevenin equivalent source voltage is given by:

RRR

[]

•

(–

)

()

•

•||(

)

–

1/2

LT1714

TxD

RxD

49.9

Ω

750k

100k

49.9

Ω

R2A

2.55k

R3A

124

Ω

ROA

140

Ω

ROB

140

Ω

R1B

499

Ω

6-FEET

TWISTED PAIR

ZO ≈ 120Ω

R1D

499

Ω

R1C

499

Ω

R3B

124

Ω

R2C

2.55k

100k

171314 F03

16 13

TxD

RxD

R3C

124

Ω

R3D

124

Ω

R2D

2.55k

R2B

2.55k

R1A

499

Ω

–

1/2

LT1714

–

750k

49.9

Ω

49.9

Ω

100k

–

1/2

LT1714

1/2

LT1714

DIODES: BAV99

×4

Figure 3. 75Mbaud Full Duplex Interface on Two Wires

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