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10
Figure 12: Lowpass Filter Topology
Figure 13: Design Equations
This example illustrates a lowpass filter with Q = 0.707
and corner frequency f
c
= 10MHz. A Q of 0.707 was
chosen to achieve a maximally flat, Butterworth
response. Figure 14 indicates the filter response.
Figure 14: Lowpass Response
Differential Line Driver With Load
Impedance Conversion
The circuit shown in the
Typical Application
schematic
on the front page and in Figure 15, operates as a
differential line driver. The transformer converts the load
impedance to a value that best matches the CLC5622’s
output capabilities. The single-ended input signal is
converted to a differential signal by the CLC5622. The
line’s characteristic impedance is matched at both the
input and the output. The schematic shows Unshielded
Twisted Pair for the transmission line; other types of lines
can also be driven.
Figure 15: Differential Line Driver wtih
Load Impedance Conversion
Set up the CLC5622 as a difference amplifier:
Make the best use of the CLC5622’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 CLC5622 also affects the match. With
an ideal transformer we obtain:
M
Frequency (Hz)
3
0
-3
-6
-9
-12
-15
-18
-21
-24
-27
-30
1M
10M
100M
Gain
K
1
R
R
Corner frequency
1
R R C C
Q
1
R C
R C
R C
R C
(1 K)
R C
R C
For R
R
R and C
C
C
1
RC
Q
1
(3 K)
f
g
c
2
2
1
2
1
2
c
=
= +
=
=
=
+
+
=
=
=
=
=
=
ω
ω
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 5622
o
( )
)
ω
+
1/2
CLC5622
R
g2
+
V
o
-
-
R
t2
R
f2
R
f1
R
g1
1/2
CLC5622
V
in
R
t1
R
m/2
R
m/2
R
L
Z
o
UTP
I
o
R
eq
1:n
V
d/2
-V
d/2
+
-
R
f
1k
0.1
μ
F
C
1
V
o
V
in
R
g
0.1
μ
F
5k
4
0.1
μ
F
5k
R
1
158
3
2
+5V
0.1
μ
F
100
1.698k
R
2
158
C
2
100pF
1/2
CLC5622
8
1