CPC5604
Return Loss
The return loss is a measure of impedance mismatch
between a terminating impedance (DAA) and a source
impedance (reference impedance). The AP measures
the return loss vs. frequency with the addition of the
bridge circuit show in Figure 7A. For this test, the refer-
ence impedance is set by the 600Ω nominal imped-
ance, ZREF. The impedance that this is to be compared
to is across Tip and Ring connections. The AP sweeps
frequency and graphs frequency vs. return loss as
shown in Figure 7B.
Figure 7A Return Loss Test Setup
V
X
40mA Loop Current
Z
REF
TIP
500
10H
600
600
Audio
+
-
48V
LITELINKTM DAA Circuit
Precision
Generator
+
50
A
V
GEN
OH
RING
500
10H
-
-A+
+B-
V
X
RL (dB) = 20 log
V
GEN
Audio Precision System
One Analyzer
*Note: 0.1% Component tolerances should be used
for accurate measurements
Figure 7B Return Loss
-10
-12
-14
-16
-18
-20
-22
-24
-26
-28
-30
RL
(dBm) -32
-34
-36
-38
-40
-42
-44
-46
-48
-50
500
1K
1.5K
2K
2.5K
3K
3.5K
4K
Frequency (Hz)
XXX
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