TEA0675T PHILIPS [NXP Semiconductors], TEA0675T Datasheet - Page 11

• Manufacturer Part Number: TEA0675T
• Description: Dual Dolby* B-type noise reduction circuit for playback applications
• Manufacturer: PHILIPS [NXP Semiconductors]

Philips Semiconductors
Description of the principle timing diagram for AMS-scan mode without initial input signal (see Fig.5)
By activating AMS-scan mode, the AMS output level
directly indicates whether the input level corresponds to a
pause level (V
At t
V
output changes to LOW level: due to no signal at V
voltage at the level detector input V
remains below the level threshold and the second time
constant will be discharged (time detector input V
When V
output changes to LOW level. Now the initial procedure is
completed.
If a signal burst appears at t
voltage rises immediately and causes its output to charge
the second time constant, which supplies the input voltage
V
1996 Jun 07
in
t
Dual Dolby* B-type noise reduction circuit
for playback applications
for the time detector. When V
, the following initial procedure runs until the AMS
0
the AMS-scan mode is activated. Without a signal at
t
passes the time threshold level, the time detector
handbook, full pagewidth
t r : rise time
t d : delay time
t b : burst time
t p : pause time
t f : fall time
AMSEQ
to microprocessor
upper threshold
level threshold
time threshold
output signal
(hysteresis)
V AMSEQ
= LOW) or not (V
V REF
4.5 V
V in
V l
V t
3
AMS on
, the level detector input
t 0
t
passes the upper
Fig.5 AMS-scan mode without initial input signal.
I
(pin 3, CONTRA)
AMSEQ
t 3 t 4
t r
= HIGH).
t 5 t 6
t
).
in
t f
t d
the
t 7
11
threshold level after the rise time t
changes to HIGH. If the signal burst ends at t
detector input V
level threshold at t
constant begins. Now the circuit measures the delay time
t
length of a pause to be detected. If no signal appears at V
within the time interval t
the AMS output to LOW level at t
If a plop noise pulse appears at V
less than the rise time t
detected as music. The AMS output remains LOW.
Similarly the system handles ‘no music pulses’ t
music appears at t
interruption will not affect the AMS output for t
d
t 8 t 9 t 10
, which is externally fixed by a resistor and defines the
t b t r
t 11 t 12
I
falls to its LOW level. When passing the
6
11
, the discharging of the second time
t 13 t 14
with a small interruption at t
d
r
t p t d
, the time detector output switches
> t
b
, the plop noise will not be
t 15
V l : voltage at
pin 3 (CONTRA)
V t : voltage at
pin 22 (CONTRB)
7
Preliminary specification
in
r
level detector
input
time detector
input
.
(at t
(t
8
) with a pulse width
4
MED625
), the AMS output
TEA0675
t
t
t
t
5
p
the level
< t
p
13
: when
d
, this
.
in