TEA0675T データシートの表示（PDF） - Philips Electronics

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TEA0675T

Dual Dolby* B-type noise reduction circuit for playback applications

Philips Electronics 

Philips Semiconductors

Dual Dolby* B-type noise reduction circuit

for playback applications

Preliminary specification

TEA0675

Short description ‘music search’

A system for ‘music search’ mainly consists of a level and

a time detection (see Fig.4). For adapting and decoupling

the input signal will be amplified (A), then rectified (B) and

smoothed with a time constant (C). So the voltage at (C)

corresponds to the signal level and will be compared to the

predefined pause level at the first comparator (D), the level

detector. If the signal level becomes smaller than the

pause level, the level detector changes its output signal.

Due to the output level of the level detector the capacitor

of the second time constant (E) will be charged,

respectively discharged. If the pause level of the input

signal remains for a certain time, the voltage at the

capacitor reaches a certain value, which corresponds to

an equivalent time value. The voltage at the capacitor will

be compared to a predefined time-equivalent voltage by

the second comparator (F), the time detector. If the pause

level of the input signal remains for this predefined time,

the time detector changes its output level for ‘pause found’

status.

handbook, full pagewidth

(A)

INPUT

(B)

(C)

(D)

(E)

(F)

COMPARATOR 1

t1

VI

COMPARATOR 2

t2

Vt

OUTPUT

AMPLIFIER RECTIFIER

LEVEL DETECTOR

TIME DETECTOR

MED624

Fig.4 Integrated ‘music search’ function.

1996 Jun 07

10

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