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TEA0679

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

Short description of music search

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

time detection circuit (see Fig.4). For adapting and

decoupling the input signal is amplified (A), then rectified

(B) and smoothed with a time constant (C). Thus 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 period, 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 to 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.

1998 Nov 12

11

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