TDA7335 datasheet(8/20 Pages) STMICROELECTRONICS

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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 C9x 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.

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:

Vin

= AMSVth

+ R8

101K

+ R8 ⋅

0.6

where Vin is the mean of left and right channels:

Vin

Vright

+ Vleft

(4): the charging current at pin 9 is about 20

µA

(half input signal) so program detection time

constant is given by:

C7 x 2Vbe

µA

= 70 x C7 [µF] = [msec]

It is recommended to insert a resistor (R7) high

enough to prevent fast C7 capacitor discharging.

AMS Gin

0.22

µF

IN-L

100K

Rp21

IN-R

LIMITER

AMPLIFIER

Vth0

SIGNAL DETECT.

COMPARATOR

POWER-ON

RESET

AMS th

NOR1

Vth1

AMS OUT

FF2

COMP1

COMP2

FF1

0.1

µF

500K

PROGRAM

DETECTION TIME

C15

SPACE

DETECTION

TIME

INTS

AMS SW

INTP

D93AU098

Figure 2: Audio Music Sensor

TDA7335

8/20

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