11

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

potential difference.

The circuit works well with the resistor values shown, but

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

The input impedance of the resistive network should

match the characteristic impedance and is given by:

RR

RR

R

RR

R

R

IN

O

O

=

+

++

[]

2

12

3

21

2

3

••

||(

)

•||(

)

This comes out to 120

Ω for the values shown. The

Thevenin equivalent source voltage is given by:

VV

RR

R

RRR

R

RR

R

R

TH

S

O

O

=

+

++

++

[]

•

(–

)

()

•

•||(

)

23

1

23

1

21

2

3

–

+

1/2

LT1714

TxD

RxD

7

8

9

LE

6

5

49.9

Ω

750k

750k

100k

100k

49.9

Ω

2

1

15

3

16

13

14

3V

3V

4

11

12

R2A

2.55k

R3A

124

Ω

140

Ω

140

Ω

R1B

499

Ω

6-FEET

TWISTED PAIR

R1D

499

Ω

R1C

499

Ω

R3B

124

Ω

R2C

2.55k

3V

100k

5

11

2

1

12

6

10

9

8

7

171314 F03

14

3

15

16 13

4

TxD

RxD

3V

R3C

124

Ω

R3D

124

Ω

R2D

2.55k

R2B

2.55k

R1A

499

Ω

10

–

+

1/2

LT1714

LE

–

+

750k

750k

49.9

Ω

49.9

Ω

100k

–

+

LE

1/2

LT1714

LE

1/2

LT1714

3V

3V

DIODES: BAV99

×4

Figure 3. 75Mbaud Full Duplex Interface on Two Wires