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TEA0675T View Datasheet(PDF) - Philips Electronics

Part Name
Description
Manufacturer
TEA0675T Datasheet PDF : 32 Pages
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Philips Semiconductors
Dual Dolby* B-type noise reduction circuit
for playback applications
Preliminary specification
TEA0675
Description of the principle timing diagram for AMS-scan mode without initial input signal (see Fig.5)
handbtro:orki,sfeulltipmaegewidth
AMS on
tr
tb<tr
td: delay time
td
tb: burst time
tp: pause time
tf: fall time
Vin
tf
tp<td
t
Vl
level threshold
VREF
Vt
upper threshold
(hysteresis)
time threshold
Vl: voltage at
level detector
input
pin 3 (CONTRA)
t
Vt: voltage at
time detector
input
pin 22 (CONTRB)
VAMSEQ
4.5 V
output signal
to microprocessor
t0
t3 t4
t5 t6
t7
t8 t9 t10
t11 t12 t13 t14
t15
Fig.5 AMS-scan mode without initial input signal.
t
t
MED625
By activating AMS-scan mode, the AMS output level
directly indicates whether the input level corresponds to a
pause level (VAMSEQ = LOW) or not (VAMSEQ = HIGH).
At t0 the AMS-scan mode is activated. Without a signal at
Vin, the following initial procedure runs until the AMS
output changes to LOW level: due to no signal at Vin the
voltage at the level detector input VI (pin 3, CONTRA)
remains below the level threshold and the second time
constant will be discharged (time detector input Vt).
When Vt passes the time threshold level, the time detector
output changes to LOW level. Now the initial procedure is
completed.
If a signal burst appears at t3, the level detector input
voltage rises immediately and causes its output to charge
the second time constant, which supplies the input voltage
Vt for the time detector. When Vt passes the upper
threshold level after the rise time tr (at t4), the AMS output
changes to HIGH. If the signal burst ends at t5 the level
detector input VI falls to its LOW level. When passing the
level threshold at t6, the discharging of the second time
constant begins. Now the circuit measures the delay time
td, which is externally fixed by a resistor and defines the
length of a pause to be detected. If no signal appears at Vin
within the time interval td, the time detector output switches
the AMS output to LOW level at t7.
If a plop noise pulse appears at Vin (t8) with a pulse width
less than the rise time tr > tb, the plop noise will not be
detected as music. The AMS output remains LOW.
Similarly the system handles ‘no music pulses’ tp: when
music appears at t11 with a small interruption at t13, this
interruption will not affect the AMS output for tp < td.
1996 Jun 07
11
 

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