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6
Set up the CLC5665 as a difference amplifier.
determined by:
V
d
is
Make the best use of the CLC5665’s output drive
capability as follows:
where R
eq
is the transformed value of the load imped-
ance, V
max
is the Output Voltage Range, and I
max
is the
maximum Output Current.
Match the line’s characteristic impedance:
Select the transformer so that it loads the line with a
value very near Z
o
over frequency range. The output
impedance of the CLC5665 also affects the match. With
an ideal transformer we obtain:
where Z
o(5665)
(j
ω
) is the output impedance of the
CLC5665 and |Z
o(5665)
(j
ω
)| << R
m
.
The load voltage and current will fall in the ranges:
The CLC5665’s high output drive current and low
distortion make it a good choice for this application.
Full Duplex Cable Driver
The circuit shown in Figure 8 below, operates as a full
duplex cable driver which allows simultaneous transmis-
sion and reception of signals on one transmission line.
The circuit on either side of the transmission line uses are
CLC5665 as a cable driver, and the second CLC5665 as
a receiver. V
oA
is an attenuated version of V
inA
, while V
oB
is an attenuated version of V
inB
.
Figure 8: Full Duplex Cable Driver
R
m1
is used to match the transmission line. R
f2
and R
g2
set the DC gain of the CLC5665, which is used in a
difference mode. R
t2
provides good CMRR and DC
offset. The transmitting CLC5665’s are shown in a unity
gain configuration because they consume the least
power of any gain, for a given load. For proper operation
we need R
f2
= R
g2
.
The receiver output voltages are:
where A is the attenuation of the cable, Z
o(5665)
(j
ω
) is
the output impedance of the CLC5665, and
|
Z
o(5665)
(j
ω
)
|
<< R
m1
.
We selected the component values as follows:
I
R
f1
= 1.2k
, the recommended value for
CLC5665 at unity gain
I
R
m1
= Z
o
= 50
, the characteristic impedance
of the transmission line
I
R
f2
= R
g2
= 750
≥
R
m1
, the recommended
value for the CLC5665 at A
v
= 2
)–R
2
I
These values give excellent isolation from the other input:
The CLC5665 provides large output current drive, while
consuming little supply current, at the nominal bias point.
It also produces low distortion with large signal swings
and heavy loads. These features make the CLC5665 an
excellent choice for driving transmission lines.
V
V
2
1
R
R
2
R
R
d
in
f1
g1
f2
g2
=
+
=
R
R
2 V
I
m
eq
max
max
+
=
R
R
Z
R
n
R
R
L
o
m
eq
L
eq
=
=
=
ReturnLoss
20 log
=
n
Z
j
Z
,dB
10
2
o 5665
o
( )
)
ω
V
n V
I
I
n
o
o
≤
≤
max
max
R
f1
R
f2
+
-
R
t1
Z
0
-
+
CLC5665
V
inA
R
g2
R
t2
R
m1
V
oB
R
f1
R
f2
+
-
R
t1
-
+
V
inB
R
g2
R
t2
R
m1
V
oA
CLC5665
CLC5665
CLC5665
V
V
A
V
2
1
R
R
Z
(j )
R
outA(B)
inA(B)
inB(A)
f2
g2
o(5665)
m1
≈
+
+
R
(R
||R
25
t2
f2
g2
m1
=
=
V
V
38dB, f
≈
5.0MHz
oA(B)
inB(A)
=