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TEA0679T

I2C-bus controlled dual Dolby* B-type noise reduction circuit for playback applications

Philips Electronics 

Philips Semiconductors

I2C-bus controlled dual Dolby* B-type noise

reduction circuit for playback applications

Product specification

TEA0679T

Description of the principle timing diagram for AMS

scan mode without initial input signal (see Fig.5)

By activating the 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 a LOW level: due to no signal at Vin the

voltage at the level detector input VI (CONTRA) remains

below the level threshold and the second time constant will

be discharged (time detector input Vt). When Vt exceeds

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 exceeds 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. Discharging of the second time constant begins

when the level threshold is exceeded at t6. The circuit then

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 a 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.

handbook, full pagewidth

AMS on

tr

td

tf

Vin

tb < tr

tp < td

t

Vl

level threshold

Vref

Vt

upper threshold

(hysteresis)

time threshold

Vl: voltage at

level detector

input

pin 8 (CONTRA)

t

Vt: voltage at

time detector

input

pin 25 (CONTRB)

VAMSEQ

4.5 V

output signal

to microprocessor

t0

t3 t4

t5 t6

t7

t8 t9 t10

tr = rise time; td = delay time; tb = burst time; tp = pause time; tf = fall time.

t11 t12 t13 t14

t15

Fig.5 AMS scan mode without initial input signal.

t

t

MHB120

1998 Nov 12

12

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