U4030B Datasheet PDF - TEMIC Semiconductors
Part Number | U4030B | |
Description | Telephone Speech Circuit | |
Manufacturers | TEMIC Semiconductors | |
Logo | ||
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Telephone Speech Circuit
U4030B
Description
The U4030B is an electronic speech circuit for standard
and feature telephones. It replaces the hybrid transformer,
earphone and microphone interface and the supply
voltage generation for external components, e.g. dialer or
microcomputers. Using the U4030B in telephone circuit
designs can improve transmission quality and results in
cost savings through shorter and more flexible design
procedures. It reduces the amount of external components
needed. The U4030B uses TEMIC’s reliable bipolar
technology and is offered in a SO20 package.
Features
D Microphone amplifier with
– Symmetrical input
– Privacy function
– Anticlipping
D Built in ear protection
D Power down input
D Mute input
D DTMF interface
D Low line impedance during pulse dialing
Benefits
D Independent adjustment of
– Transmission gain
– Receiving gain
– Sidetone suppression
– Frequency response
D Low-impedance supply voltage for all external blocks
D Supply voltage for an electret microphone
Applications
D Standard telephone
D Fax machine
D Answering machine
D Cordless telephone
Block Diagram
10
DTMF
PRIV
MIC1
MIC2
16
12
13
GT MICO
11 9
–
+
ST
5
+
–
TXA
GR RECO
67
+–
Ear protection
REC.ATT.
4 CK
Limiter
3
CLIM
Mute
8
MUTE
17
PD
Power supply
U 4030 B
14
GND
18 1
SWAMP VM
15 VL
19 RDC
2 VC
20
VD
Figure 1.
Ordering Information
93 7618 e
Extended Type Number
U4030B-AFL
U4030B-AFLG3
Package
SO20
SO20
Remarks
Taped and reeled
Rev. A2, 27-Jan-98
1 (14)
|
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U4030B
Transmit Output Amplifier
The output signal of the microphone and DTMF
preamplifier is internally coupled to a second amplifier
( TXA) which is used to modulate a controlled current
source. Assuming a termination of 600 W at a line, the
gain from MICO to VL is typically 15.6 dB.
Receive Amplifier
The receive signal is taken from line via capacitor CCK.
A resistive attenuator ( –32 dB ) sets the appropriate input
level for the following output amplifier. The input
impedance at Pin 4 is typically 80 kW.
Voltage gain is:
GR = 20 log ( Vear / VL ) dB
= –32 dB + 20 log [ ( RR1 / RR2 ) + 1 ] dB
= +1.8 dB
The adjustment range for receive gain GR is typically
–4 dB to + 8 dB.
The built-in ear protection limits the output swing at Pin
7 to 2.4 Vpp ( VD > 4 V). For high receive gain, the
maximum undistorted output level might not be sufficient
due to clipping by ear protection.
Sidetone
The amplified microphone signal is available at the input
of the sidetone loop, MICO. The loop consists of a
transmit amplifier ( transconductance STX ), the
impedance at line, receive attenuator ( gain) and the side-
tone network ( figure 7 ).
The sidetone cancellation is achieved by comparing a part
of the line signal with the output of the sidetone network
( VST → VR). Assuming a real impedance of the tele-
phone ( RTel ) the optimum sidetone network can be
calculated:
a = ( STX RAPP G ) / ( 1 – STX RAPP G )
ZNW = STX R G ZLine
Adjustment to the sensitivities of the handset can be done
independently from the sidetone network because receive
and transmit gain are set outside of the sidetone loop.
Power Down (PD)
The speech circuit is switched low ohmic by selecting a
high level at PD during the pulse dialling. The voltage
drop across the IC will be typically 1.5 V. During this time
the capacitor CVD will not be discharged, because an
internal power down switches off all internal amplifiers.
In order to avoid cracks, it is recommended to activate
power down while sending the dial pulses ( figure 8 ).
R
aR ZNW
MICO
Mic.
+ V ST
– VR
G = 1/40
VL
VH
STX = 18.8 mS
RTEL
ZL
Figure 7. Schematic of the sidetone
93 7624 e
Rev. A2, 27-Jan-98
5 (14)
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Information | Total 14 Pages | |
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