TDA7335 Datasheet, PDF (8/20 Pages) STMicroelectronics – STEREO PREAMP AMS DOLBY B* NOISE REDUCTION PROCESSOR

TDA7335
c)From now on where the sum input signal (left-
right) amplified by the limiter exceeds the sig-
nal detector threshold (3) the capacitor C7 is
forced to charge. When the voltage across
this capacitor reaches the comparator
COMP1 threshold voltage Vth1 (approx. 2 Vbe)
FF1 is set and FF2 is reset. (4) It follows that
Q1 is turned on discharging the program de-
tection capacitor (C7).
d)Always when there is a recorded zone, Q1 is
on; it becomes off only if a blank section is
reached. When, with a time constant control-
led by the R9, C9 network the voltage at
space detection time pin reaches Vth2 thresh-
old (comparator COMP2) a true blank section
is detected and the FF2 is set. (The minimum
charging time is approximately given by:
0.69 x C9 x R9 [sec]
In this condition Q2 is ON, forcing the open
collector AMS output to go LOW, informing
the user that a true blank section has been
detected. The state is then able to start from
the above point c). Figures 3-4 show the sig-
nal behaviour.
Figure 2: Audio Music Sensor
The device is able to prevent false interspace de-
tection and the end of the tape. (see Fig. 4).
Note:
(3): minimum RMS input signal is given by:
V_in =
AMSVth
=
1K + R₈
101K + R₈
⋅
0.6
where Vin is the mean of left and right channels:
Vin =^Vright₂^{+ Vleft}
(4): the charging current at pin 9 is about 20µA
(half input signal) so program detection time
constant is given by:
C₇ x 2V_be
20µA
=
70
x
C₇
[µF]
=
[msec]
It is recommended to insert a resistor (R7) high
enough to prevent fast C7 capacitor discharging.
AMS Gin 21
1K
100K
0.22µF
C8
RB
6
IN-L
25
IN-R
Rp21
Vs
+
R9
-
+
LIMITER
AMPLIFIER
SIGNAL DETECT.
COMPARATOR
Vth0
AMS th
Vs
NOR1
Q1
22
AMS OUT
POWER-ON
RESET
Q2
R
FF2
Q
S
COMP2
+
-
COMP1
Vth1
Q
S
FF1
Q
R
9 INTP
0.1µF
C7
R7
500K
PROGRAM
DETECTION TIME
23
8
AMS SW
C15
T1
10
INTS
R9
SPACE
C9
DETECTION
TIME
Vs
T2
D93AU098
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