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TEA0678 View Datasheet(PDF) - Philips Electronics

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TEA0678 Datasheet PDF : 28 Pages
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Philips Semiconductors
Dual Dolby* B-type noise reduction circuit, automatic
music search, with differential outputs and mute
Preliminary specification
TEA0678
Description of the principle timing diagram for AMS-scan mode with initial input signal (see Fig.6)
handbtro:orki,sfeulltipmageewidth
td: delay time
tb: burst time
tp: pause time Vin
tf: fall time
AMS on
td
tb<tr
tf
tp<tr
t
Vl
level threshold
VREF
Vt
upper threshold
(hysteresis)
time threshold
Vl: voltage at
level detector
input
pin 7 (CONTRA)
t
Vt: voltage at
time detector
input
pin 26 (CONTRB)
VAMSEQ
4.5 V
output signal
to microprocessor
t0 t1
t5 t6
t7 t8 t9 t10
t11 t12 t13 t14
t15
Fig.6 AMS-scan mode with initial input signal.
t
t
MED774
At t0 the AMS-scan mode is activated. With an input signal
at Vin, the following initial procedure runs until the circuit
gets a steady state status.
Due to the signal at Vin the voltage at the level detector
input VI (pin 7, CONTRA) slides to a value which is defined
by a limiter. This voltage causes the level detector output
charging the second time constant (time detector input Vt)
to its maximum voltage level at t1. Now the initial
procedure is completed.
The following behaviour does not differ from the
description in Section “Description of the principle timing
diagram for AMS-scan mode without initial input signal
(see Fig.5)”.
1996 Jun 06
13
 

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