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參數(shù)資料
| 型號： | U3900BM-AFN |
| 英文描述： | Programmable Telephone Audio Processor |
| 中文描述： | 程控電話音頻處理器 |
| 文件頁數(shù)： | 17/34頁 |
| 文件大小： | 762K |
| 代理商： | U3900BM-AFN |
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U3900BM
Rev. A2, 25-Aug-98
Target Specification
24 (34)
13 Sidetone System
The Sidetone Balancing (STB) has the task to reduce the
crosstalk from LTX (microphone) to LRX (earpiece) in
the frequency range of 0.3 to 3.4 kHz. The LTX signal is
converted into a current in the MOD block. This current
is transformed into a voltage signal (LINE) by the line
impedance ZL. The LINE signal is fed into the summing
amplifier DIFF1 via capacitor CK and attenuator AMP1.
On the other side the LTX buffered by STOAMP drives
an external low-pass filter (RST, CST). The external low-
pass filter and the internal STB have the transfer function
drawn in the STB box. The amplified STB-output signal
drives the negative input of the summing block. If both
signals at the DIFF1 block are equal in level and phase,
we have a good suppression of the LTX signal. In this
condition the frequency and phase response of the STB
block will represent the frequency curve on line.
In real live the line impedance ZL varies strongly for
different users. To reach a good suppression with one
application for all different line impendances, the STB
function is programmable.
The 3 programmable parameters are
1.
LF (gain at low frequency).
LF has 15 programming steps. LF(0) gives –2 dB
gain, LF(15) gives 5.5 dB gain.
LF
0
1
2
3
4
5
6
7
Step gain
–2
–1.3
–0.6
0.1
0.6
1.0
1.3
1.6
LF
8
9
10
11
12
13
14
15
Step gain
1.9
2.2
2.5
3.0
3.6
4.2
4.8
5.5
STO_DIFF(LF) = (–10 dB – 2 dB + 0.5 dB
LF + 9 dB)
LTX
2.
P (the pole position of the lowpass).
The P adjustment has 31 Steps. P(0) means the
lowpass determined by the external application
(RST, CST). The internally processed low-pass
frequency is fixed by this equation.
f(P)
+
1
2
p
CST
RST
1.122
P
3.
SL
(sidetone slope; the pole frequency of the highpass)
The SL have 3 steps. SL(0) is a lower frequency of the
highpass. SL(3) is a higher frequency of the highpass.
With SL we can influence the suppression at high
frequencies.
14579
–10dB
LF
f
P
SL
g
STC
STRC
0–7dB
STOAMP
STO
8.2 k
STO
CTO
33 nF
8dB
MOD
RECIN
LINE
–10dB
AMP1
9dB
STO_DIFF
DIFF1
AMP2
+
–
AGARX
LTX
LRX
CK
ZL
Sidetone balancing
LF
P
SL
Figure 26. Programmable sidetone supression circuit
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