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

SYMBOL

PARAMETER

CONDITIONS

MIN.

TYP.

MAX. UNIT

AP/M

signal level at output for AMS mode; f = 10 kHz;

−24

AMS switching

pause to music

−21

−18

dB

EQ switch input (not AMS mode)

IEQ70

IEQ120

IEQth

input current

input voltage

threshold current

HEAD SWITCHING

VHSW

IHSW

VHSW(HIGH)

pin voltage

input current

HIGH level pin voltage

VHSW(LOW) LOW level pin voltage

time constant 70 µs active −150

−

−

µA

time constant 120 µs active −1000

−

−250

µA

note 1

−

−200

−

µA

load current +90 to −90 µA

VHSW = 0 to VCC

inputs INA1 and INB1

active; note 3

inputs INA2 and INB2

active

−

−170

1⁄2VCC + 0.5

0

0.8VCC

−

−

−

−

V

+170

µA

VCC

V

1⁄2VCC − 0.5 V

Notes

1. In AMS off mode, pin AMSEQ is HIGH level, the equalization time constant will be switched by pulling approximately

200 µA out of pin AMSEQ. This means for the device connected to pin AMSEQ, a restriction of input current at HIGH

level less than 200 µA during AMS off; otherwise the selection of the equalization time constant is disabled and fixed

at 120 µs. If the connected devices consume more than 200 µA, this input has to be disconnected in AMS off mode.

(To ensure switching, the currents for the different switched modes are specified with a tolerance of ±50 µA in

Chapter “Characteristics”.) For an application with a fixed EQ time constant of 120 µs the equalizing network may be

applied completely external. Change 8.2 kΩ resistor to 14 kΩ the internal resistor REQ = 5.8 kΩ is short-circuited by

fixing the EQ switch input at the 70 µs position (IEQ70).

2. The high speed of the tape (FF, REW) at the tape head during AMS mode causes a transformation of level and

frequency of the originally recorded signal. It means a boost of signal level of approximately 10 dB and more for

recorded frequencies from 500 Hz up to 4 kHz. So the threshold level of −22 dB corresponds to signal levels in Play

Back (PB) mode of approximately −32 dB. The AMS inputs for each channel are pin SCA and pin SCB. As the

frequency spectrum is transformed by a factor of approximately 10 to 30 due to the higher tape speed in FF, REW,

the high-pass filter (4.7 nF/24 kΩ) removes the effect of offset voltages but does not affect the music search function.

In the application circuit (Fig.1) the frequency response of the system between tape heads input, e.g. pins INA2 and

INB2, to the AMS input pins SCA and SCB is constant over the whole frequency range (see Fig.3).

3. To activate the inputs IN1, pin HS might be left open-circuit. In this event the DC level at pin HS is 0.775VCC.

1996 Jun 07

8

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