U4091BM TEMIC Semiconductors, U4091BM Datasheet - Page 14

• Manufacturer Part Number: U4091BM
• Description: Programmable Telephone Audio Processor
• Manufacturer: TEMIC Semiconductors

Summary of the Truth Table
1. The circuit will switch to transmit mode if
2. The circuit will switch to receive mode if
3. The circuit will switch to the reverse mode if the level
4. The circuit will switch to idle mode when
The time required to switch the circuit between transmit,
receive and idle is determined by internal current sources
and the capacitor at Pin CT. A diagram of the C
is shown in figure 13. It operates as follows:
D CCT is typically 4.7
D To switch to transmit mode, ITX is turned on (IRX is
U4091BM
14 (29)
off), charging the external capacitor to –240 mV
below VM. (An internal clamp prevents further
charging of the capacitor.)
a) Both transmit level detectors sense higher signal
b) The transmit background-noise monitor indi-
a) Both receive level detectors sense higher signal
b) The receive background-noise monitor indicates
detectors disagree on the relative strengths of the
signal levels, and at least one of the background-
noise monitors indicates speech.
a) Both talkers are quiet (no speech present), or
b) When one talker’s speech level is continuously
levels than the respective receive level detectors
and
cates the presence of speech.
levels than the respective transmit level
detectors, and
the presence of speech.
overridden by noise at the other speaker’s
location.
m
F.
Figure 13. Generation of control voltage (CT) for mode switching
C CT
CT
I
RX
10 A
I
10 A
Target Specification
TX
I FI
T
circuitry
V M
I
SI
V M
D To switch to receive mode, IRX is turned on (ITX is
D To switch to reverse mode, the current sources ITX,
D To switch to idle mode, the current sources ITX, IRX,
(TLDT)
TLDR
off), increasing the voltage on the capacitor to
+240 mV with respect to VM.
IRX are turned off, and the current source IFI is
switched on, discharging the capacitor to VM.
IFI are turned off, and the current source ISI is charg-
ing the capacitor to VM.
Control
control
circuit
AFS
V M
IN
Figure 12. Background noise monitor
33 k
+
Dial tone det.
–
56 k
Figure 11. Dial tone detector
to
attenuators
V M
4
I 1–4
+
–
35 mV
+
–
DTD
36 mV
14590
OUT
I 4
V B
+
14588
–
to mode
Rev. A1, 02-Jun-98
control
(I 3 )
I 4
(BNMT)
BNMR
14589
1 F