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參數(shù)資料
| 型號(hào)： | LS656 |
| 廠商： | 意法半導(dǎo)體 |
| 英文描述： | Telephone Speech Circuit With Multifrequency Tone Generator Interface(帶多頻語音發(fā)生器接口的電話語音電路) |
| 中文描述： | 電話語音電路多頻音發(fā)生器接口（帶多頻語音發(fā)生器接口的電話語音電路） |
| 文件頁數(shù)： | 7/15頁 |
| 文件大小： | 192K |
| 代理商： | LS656 |
The correspondingcurrent is
I =
V
7
R
3
Therefore
Z
M
=
V
6
I
= R3
1
+
R
a
R
b
The total impedance across the line connections
(pin 11and 9) is given by
Z
ML
=R1 + Z
M
//(R2 + Z
B
)
By choosing Z
M
≥
R1and Z
B
≥
Z
M
Z
ML
Z
M
= R3
1
+
R
a
R
b
Thereceived signalamplitudeacrosspin11 and10
can be changed using different value of R1 (of
course the relationship Z
L
/Z
B
= R1/R2 must be al-
ways valid).
Thereceivedsignalis relatedto R1valueaccording
to the approximatedrelationship:
V
R
=2 V
RI
R
1
R
1
+
Z
M
Notethatbychangingthevalue ofR1,thetransmis-
sionsignalcurrent is not changed,beingthe micro-
phoneamplifier a transconductanceamplifier.
3. Automatic Gain Control
The LS656 automatically adjusts the gain of the
sendingandreceivingamplifiers to compensatefor
line attenuation.
Thisfunction is performedby thecircuit of fig. 9.
The differential stage is progressively unbalanced
by changing V
G
in therange 1 to 2 V (V
REFG
is an
internal reference voltage, temperature compen-
sated).
It changesthecurrentI
G
, andthis current isusedas
a control quantity for the variablegain stages(am-
plifier (4) and(5) in the block diagram).The voltage
V
G
can be taken :
a)fromtheLS656itself(bothinvariableandinfixed
mode)and.
b) from a resistivedivider, directly at the end of the
line.
a)Inthefirst case,connectingV
G
(pin8)totheregu-
lator bypass (pin 5) it is possible to obtaina gain
characteristic dependingon the current.
In fact (see fig.6)
V
5
= V
B
+ V
7
V
B
= (I
L
-I
o
) R3
Thestartingpointoftheautomaticlevelcontrolisob-
tained at I
L
= 25 mA when the drain current
I
o
= 7.5 mA.
Minimum gain is reachedfor aline current of about
50mAforthesamedraincurrent I
o
=7.5mA.When
I
o
isincreasedbymeansoftheexternalresistorcon-
nectedto pin 4, thetwo abovementionedvalues of
thelinecurrentforthestartingpointandforthemini-
mum gain increaseaccordingly.
Itisalsopossibletochangethestartingpointwithout
changingI
o
byconnectingpin8tothecentreofare-
sistivedividerplacedbetweenpin5andground(the
total resistanceseen by pin 5 mustbe atleast 100
K
). Inthis case, the AGCrange increasestoo; for
exampleusinga division 1 : 1 (50 K/50 K) the AGC
startingpointshiftstoaboutI
L
=40mA,andthemini-
mum gain is obtained at I
L
= 95 mA. In addition to
this operation mode, the V
G
voltage can be main-
tainedconstantthusfixingthegainvalue(Rx,Tx)in-
dependentlyof the line conditions.
For this purposethe V
DD
voltage,availablefor sup-
plyingthe MFgenerator,can be used.
b) Whengains have to be related to the voltageat
the line terminals of the telephone set, it is neces-
sarytoobtainV
G
fromaresistivedividerdirectlycon-
nectedto the end of the line.
Thistypeofoperationmeetstherequirementsofthe
French standard. (See the application circuit of
fig.13).
4. TransducerInterfacing
Themicrophone amplifier (3)hasadifferentialinput
stagewith high impedance (
40k
) so allowing a
goodmatching to the microphoneby meansof ex-
ternal resistor without affecting the sending gain.
The receiving output stage (6) is particularly in-
tendedto drivedynamic capsules.(Low output im-
pedance (100
max) ; high current capability 3
mAp).
Whena piezoceramiccapsuleis used,itis usefulto
increase the receiving gain by increasing R1 value
(seethe relationshipfor V
R
).
Whit very low impedance transducer, DC decou-
pling by an externalcapacitor must be provided to
prevent a large DC current flow across the
transducer itself due to the receiving output stage
offset.
5. Multifrequency Interfacing
TheLS656actsasalinearinterfacefortheMultifre-
quency synthesizerM761accordingtoalogicalsig-
nal (mute function)present on pin 3.
When no key of the keyboardis pressed the mute
stateis low andthe LS656 feedsthe M761through
pin15withlowvoltageandlowcurrent(standbyop-
eration of the M761). The oscillator of the M761 is
not operating.
Whenone key is pressed, theM761 sends a ”high
state” mute conditionto the LS656. A voltagecom-
LS656
7/15
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相關(guān)代理商/技術(shù)參數(shù) |
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|---|---|
| LS656AB | 制造商:STMICROELECTRONICS 制造商全稱:STMicroelectronics 功能描述:TELEPHONE SPEECH CIRCUIT WITH MULTIFREQUENCY TONE GENERATOR INTERFACE |
| LS656AD1 | 制造商:STMICROELECTRONICS 制造商全稱:STMicroelectronics 功能描述:TELEPHONE SPEECH CIRCUIT WITH MULTIFREQUENCY TONE GENERATOR INTERFACE |
| LS656B | 制造商:STMICROELECTRONICS 制造商全稱:STMicroelectronics 功能描述:TELEPHONE SPEECH CIRCUIT WITH MULTIFREQUENCY TONE GENERATOR INTERFACE |
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