AN1500A South African Micro-Electronic Systems, AN1500A Datasheet - Page 10

• Manufacturer Part Number: AN1500A
• Description: Single Chip Telephone Demo Board
• Manufacturer: South African Micro-Electronic Systems

11.1.2 Measurement:
Calculation of results:
The sending level, measured in “cal”-position of switch SW is tuned to ps=-10dB
generator’s level is -4dB
The echo return loss is then calculated by:
12 Sidetone cancellation
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16
18
20
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24
26
28
30
0
Fig. 4: typ. return loss measurement results with the DB1500I demo board
Fig. 3: Return loss measurement setup
300
950mV
600
= 600mV
900
sames
sames
sames
sames
1200
rms
.The receive level (=pe) is measured in “meas”-position of switch SW.
1500
or
1800
f [Hz]
ar
ar
2100
dB
dB
= ps - pe
= 20* log (ps / pe)
2400
2700
220+820//115nF
270+750//150nF
600 Ohms
3000
3300
Echo return loss (according to BAPT223
ZV5) is measured by bridge balance
measurement as shown in Fig.3:
R1 and R2 must be matched to 0.1%,
the measuring equipment must be
isolated from earth and should have an
input resistance of >25k .
Capacitors C1 and C2 must be >10µF.
The Telephone under test is supplied by
a (high ohmic) current source and
measurements are taken in speech
mode with a connected handset.
3600
950mV
3900
(ps, pe levels in dB
(ps, pe levels in mV
= 300mV
Fig.4 shows some typical
results, measured with the
DB1500I demo board with
Z
820 //115nF
270 + 750 //150nF.
The board was configured
as shown in the schematic,
using a single bipolar
(2SA1210) line transistor.
ref
= 600 , Z
rms
,thus the sinewave
950mV
rms
ref
and
= 220
)
)
Z
ref
+
=