U4030B TEMIC Semiconductors, U4030B Datasheet - Page 5

• Manufacturer Part Number: U4030B
• Description: Telephone Speech Circuit
• Manufacturer: TEMIC Semiconductors

Rev. A2, 27-Jan-98
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
gain from MICO to V
Receive Amplifier
The receive signal is taken from line via capacitor C
A resistive attenuator ( –32 dB ) sets the appropriate input
level for the following output amplifier. The input
impedance at Pin 4 is typically 80 k
Voltage gain is:
G
The adjustment range for receive gain G
–4 dB to + 8 dB.
The built-in ear protection limits the output swing at Pin
7 to 2.4 V
maximum undistorted output level might not be sufficient
due to clipping by ear protection.
R
= 20 log ( V
= –32 dB + 20 log [ ( RR1 / RR2 ) + 1 ] dB
= +1.8 dB
pp
Mic.
( V
D
ear
> 4 V). For high receive gain, the
L
/ V
is typically 15.6 dB.
L
) dB
W
.
MICO
STX = 18.8 mS
W
Figure 7. Schematic of the sidetone
R
R
at a line, the
is typically
aR
CK
.
ZNW
Sidetone
The amplified microphone signal is available at the input
of the sidetone loop, MICO. The loop consists of a
transmit
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
phone ( R
calculated:
a
Z
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 ).
NW
= S
= ( S
VR). Assuming a real impedance of the tele-
TX
Tel
amplifier
TX
) the optimum sidetone network can be
+
–
R
R
V
V
APP
RTEL
ST
G
R
G = 1/40
( transconductance
Z
G ) / ( 1 – S
Line
V
L
U4030B
TX
ZL
R
STX ),
VH
APP
5 (14)
93 7624 e
G )
the