L38812 Просмотр технического описания (PDF) - Unisonic Technologies
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L38812 Datasheet PDF : 8 Pages
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UTC L388 12 LINEAR INTEGRATED CIRCUIT
output will influence the potential at CMP input is set by the gain of the detector, the maximum swing and R5.If a
continuous input signal is received from the microphone (>10sec.) the voltage across C4 is pulled negative(relative
to the reference)with a time constant set by C4 to e.g.5 sec. A continuous input signal is thus treated as noise. Since
the output of the noise detector is going negative it thereby counteracts the signal from the transmitter detector and
thus helping the receiver detector signal to maintain a set relation to the transmitter detector signal If the transmitter
input signal contains breaks like breath pauses the voltage at TxDetout decreases. If the voltage across C3 gets less
than the inverted voltage across C4 divided by the detector gain a rapid charge of C4 towards reference will follow
(all levels referred to the reference).If the breaks are frequent as in speech the background detector will not influence
the switching characteristic of the system. See figure.9. There is a threshold of approx. 50mV at TxDetout to prevent
the activation of background noise detection in noiseless environment. In the receiver mode some of the
loudspeaker output signal will be sensed by the microphone. In order not to treat this input signal as noise, the noise
detector goes into a hold state and “remembers” the level from the previous transmitting mode periode.
CTR Input
For full speech control (50dB attenuation between the channels) this input can be left unconnected. To set the
function to 25dB attenuation the input has to be higher than 600mV below V+. See figure 11. To set the circuit into a
mute state(results in, reduced gain in receiver channel for the DTMF confidence tone in the loudspeaker and closed
transmitter channel) a voltage below Vref has to be connected to the input. By lowering the voltage at the input
below 0.9V a condition will emerge where both receiver and transmitter channels are closed. See figure.4 and 9.
CTR
Txout
1
5
4
6
V+ 15
F3
+
F2
L388 12
Control
F6
F5
12 Rxout
16 GND
13
11
F2
100k
-F1+
-Txin 2 -
+Txin 3 +F1
8
NDet
R5
Ref.
7
9 10
TxDet CMP PxDet
+ C4
+ C3 C1 + C2
F4 - 14
Rxi
n
2 3k
Tx
3
3k
VTxin
L388 12
I
Ref.
100k
120k
16
F5
120k
-F4+
20k 14
Rx
VRxin
Figure 1. Passive networks setting the speech control function Figure 2. Receiver and transmitter channel input arrangement
Transmitter
channel output
R
CTR 1
Txout 5
C
+L
F3
4
6
R
+
15 +
R
C
F2
C
+
R
C
2-
-Txin
+Txin
3
F1
+
C
8
Mic.
C
NDet
L388 12
Control
F6
F5
7
9
TxDet CMP
Ref.
10
PxDet
12 Rxout C
Power
amplifier
input
P1
13
11
16 GND
Receiver
input
R
F4 - 14
Rxin C
C
R
C4 +
R5 +
C3
C1 + C2
Figure 3. Speech switching arrangement
UTC UNISONIC TECHNOLOGIES CO. LTD 6
QW-R108-013,A
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