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參數(shù)資料
| 型號： | AN1500A |
| 廠商： | SAMES |
| 英文描述： | SINGLE CHIP TELEPHONE DEMO BOARD |
| 中文描述： | 單芯片電話演示板 |
| 文件頁數(shù)： | 10/27頁 |
| 文件大小： | 623K |
| 代理商： | AN1500A |
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AN1500A
sames
10/27
11.1.2 Measurement:
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.
Fig. 3: Return loss measurement setup
Calculation of results:
The sending level, measured in “cal”-position of switch SW is tuned to ps=-10dB
950mV
= 300mV
rms
,thus the sinewave
generator’s level is -4dB
950mV
= 600mV
rms
.The receive level (=pe) is measured in “meas”-position of switch SW.
The echo return loss is then calculated by:
ar
dB
= ps - pe
ar
dB
= 20* log (ps / pe)
(ps, pe levels in
dB
950mV
)
(ps, pe levels in
mV
rms
)
or
Fig.4 shows some typical
results, measured with the
DB1500I demo board with
Z
ref
= 600
, Z
ref
= 220
+
820
//115nF
270
+ 750
//150nF.
The board was configured
as shown in the schematic,
using a single bipolar
(2SA1210) line transistor.
and
Z
ref
=
Fig. 4: typ. return loss measurement results with the DB1500I demo board
12 Sidetone cancellation
12
14
16
18
20
22
24
26
28
30
0
300
600
900
1200
1500
1800
2100
2400
2700
3000
3300
3600
3900
f [Hz]
E
600 Ohms
220+820//115nF
270+750//150nF
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