LT1713 LINER [Linear Technology], LT1713 Datasheet - Page 11

• Manufacturer Part Number: LT1713
• Manufacturer: LINER [Linear Technology]

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 V
potential difference.
TYPICAL APPLICATIO S
RxD
TxD
13
49.9
49.9
750k
750k
14
16
LE
4
3
LT1714
3V
7
8
1/2
15
+
–
LT1714
+
–
9
LE
1/2
3V
2
1
5
6
100k
100k
10
11
12
S
up or down) of ground
U
R2A
2.55k
R3A
124
R3B
124
R2B
2.55k
Figure 3. 75Mbaud Full Duplex Interface on Two Wires
499
R
140
R1B
499
R1A
OA
3V
DIODES: BAV99
TWISTED PAIR
Z
O
6-FEET
120
The circuit works well with the resistor values shown, but
other sets of values can be used. The starting point is the
characteristic impedance, Z
The input impedance of the resistive network should
match the characteristic impedance and is given by:
This comes out to 120
Thevenin equivalent source voltage is given by:
4
R
V
IN
TH
2
3V
V
•
S
499
140
R
499
•
•
R1C
R
R1D
O
OB
R
(
(
R
R
•
O
2
2
R
O
124
124
2
2.55k
2.55k
R
R
R3D
R2D
R2C
R3C
•
3
3
R
2
R
–
1
•
R
1
||(
R
R
O
||(
R
1
1
R
)
)
O
1
for the values shown. The
R
2
, of the twisted-pair cable.
||(
LT1713/LT1714
12 6
2
100k
100k
R
11
R
2
R
3
10
LT1714
5
)
3
3V
2
1
1/2
)
R
LE
+
–
LT1714
9
3
+
–
1/2
)
3
3V
7
8
15
4
LE
171314 F03
750k
750k
16 13
49.9
49.9
14
11
RxD
TxD