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參數(shù)資料
| 型號： | TEA7092TQT |
| 廠商： | 意法半導體 |
| 英文描述： | TELEPHONE ANALOG FRONT END |
| 中文描述： | 電話模擬前端 |
| 文件頁數(shù)： | 33/57頁 |
| 文件大?。?/td> | 574K |
| 代理商： | TEA7092TQT |
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LS AGC
R31
C19
6
LSSOF
V
LS
Vp(LSOUT)
GND + 0.2
V
LS
- 0.2
Vp(LSOUT)
4
μ
A
TEA7092
A
Figure48
III - CALLPROGRESS MONITOR AND GROUP LISTENING MODES
(continued)
III.3 - Softclipping Stage
The softclippingstageavoidsdistortionontheloud-
speaker output LSOUT (Pin 44) over a range of
input signals on Pin LSIN (Pin 5).
Figure 48 shows the loudspeaker softclipping
stage.
The softclippingstage avoidsdistortionwhen there
is
not enough DC
supply voltage on
Pin V
LS
(Pin1). This is doneby detectingthe satu-
ration on the Pin LSOUT (Pin 44) compared to
Pin V
LS
(Pin 1) - 0.2V and GND + 0.2V. When one
of these two voltages is reached, the DC voltage
on Pin LSSOF (Pin 6) increases and the loud-
speaker amplifier gain is reduced through the
V
PP
(LSOUT) signal control.
III.4 - Antiacoustic Feedback Features
The same stageis used to controlthe antiacoustic
feedback stage, to avoid howling effect, than to
control the squelchstage.
Figure 49 shows the antiacoustic feedback and
squelch stage.
In grouplisteningmode, whenthe handsetandthe
loudspeakeraresimultaneouslyused, itis necces-
sary to avoid howling effect between the handset
microphoneand the loudspeaker.
The antiacousticfeedbackstagedetectsthemicro-
phone signaland,if thisoneis higher thanthe fixed
threshold (60mV), the gain of the loudspeaker is
reduced through LS AGC information.
By defaulttheloudspeakeramplifier gainreduction
is fixed at 15dB, this one can be modified through
the serialbus interfacewith the following values :
- 10dB: code(0111100).
- 15dB: code(0111101),
equivalent to default mode.
- 20dB: code(0111110).
- 25dB: code(0111111).
These different values allow the adaption of the
antiacousticfeedback stage to differenttelephone
sets.
Figure50 shows the behaviour of the antiacoustic
feedbackstage (coupled with the squelchfeature,
if thisone is enabled).
The signal microphone is amplified by the first
stage with a gain close to 200, and filtering on
Pin ASC (Pin 18), the cut off frequency is fixedby
C25 and the internal0.5k
.
Recommendedvalues :
C25 = 470nFor 1
μ
F
f
C
= 677Hzor 318Hz
On Pin ASQ (Pin 17),the rise and decaytimes are
fixed by R16, C16 and the 10
μ
A internal current
source.
- Rise time : t
R
=
C16 x 60 x 10
3
10 x 10
6
with C16 = 1
μ
F
t
R
= 6ms.
- Decaytime : t
D
= R16 x C16,
withR16=330k
andC16=1.5
μ
F
t
D
=330ms.
,
TEA7092 - TELEPHONE SET INTEGRATEDCIRCUIT
33/57
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