U4084B Datasheet, PDF (12/26 Pages) TEMIC Semiconductors – Low-Voltage, Voice-Switched Circuit for Hands-Free Operation

U4084B
The single output of the control block controls the two
attenuators. The effect of C1–C4 is as follows:
b) the transmit background-noise monitor indicates
the presence of speech
Inputs
Output
C1
C2
C3
C4
Mode
T
T
1
X
Transmit
T
R
Y
Y
Fast idle
R
T
Y
Y
Fast idle
R
R
X
1
Receive
T
T
0
X
Slow idle
T
R
0
0
Slow idle
R
T
0
0
Slow idle
R
R
X
0
Slow idle
X = don’t care; Y = C3 and C4 are not both 0.
Terms Definition
11. “Transmit” means the transmit attenuator is fully on
(+ 6.0 dB), and the receive attenuator is at max. atten-
uation (– 46 dB).
12. “Receive” means both attenuators are controlled by
the volume control. At max. volume, the receive
attenuator is fully on (+ 6.0 dB), and the transmit
attenuator is at max. attenuation (– 46 dB).
13. “Fast Idle” means both transmit and receive speech
are present in approximately equal levels. The
attenuators are quickly switched (30 ms) to idle until
one speech level dominates the other.
14. “Slow Idle” means speech has ceased in both transmit
and receive paths. The attenuators are then slowly
switched (1 s) to idle mode.
[ 15. Switching to the full transmit of receive modes from
any other mode is at the fast rate ( 30 ms).
Summary
1. The circuit will switch to transmit mode if:
a) both transmit level detectors sense higher signal
levels relative to the respective receive level
detectors (TLI1 versus RLI1, TLI2 versus RLI2),
and
2. The circuit will switch to receive mode if:
a) both receive level detectors sense higher signal
levels relative to the respective transmit level
detectors, and
b) the receive background-noise monitor indicates
the presence of speech
3. The circuit will switch to fast idle mode if the level
detectors disagree on the relative strengths of the
signal levels, and at least one of the background-
noise monitors indicates speech. If, e.g., there is a
signal at the microphone amp output (TLI2) to over-
ride the speaker signal (RLI2) and there is sufficient
signal at the receive input (RLI1) to override the
signal at the hybrid output (TLI1), and either one or
both background monitors indicate speech, then the
circuit switches to fast idle mode.
Undesired switching to idle mode may occur if one
of the following conditions is met:
a) when both persons speaking try to talk at the
same time, and
b) when one of the persons speaking is in a very
noisy environment, forcing the other one to con-
tinually override that noise level.
In general, fast idle mode occurs rarely.
4. The circuit will switch to slow idle mode when
a) both persons at the phone are quiet (no speech
present), or
b) when the speech levelof one of the persons
talking is continuously overriden by noise at the
other speaker’s location.
The time required to switch the circuit between
transmit, receive, fast idle and slow idle mode is
deter-mined in part by the components at Pin 11,
(see the section “Switching Times” for a more
detailed explanation). A schematic of the C_T
circuitry is shown in figure 6.
12 (26)
TELEFUNKEN Semiconductors
Preliminary Information
Rev. A1, 31-Jan-97