1996 Jun 06

5

Philips Semiconductors

Preliminary specification

Dual Dolby* B-type noise reduction circuit, automatic

music search, with differential outputs and mute

TEA0678

FUNCTIONAL DESCRIPTION

Noise Reduction (NR) is enabled when pin NR/AMS is

connected to ground and disabled when open-circuit (left

floating from a 3-state output).

Dolby noise reduction only operates correctly if 0 dB Dolby

level is adjusted at 387.5 mV.

Automatic Music Search (AMS) is enabled when pin

NR/AMS is connected to HIGH (5 V) and disabled when

open-circuit (left floating from a 3-state output). In AMS

mode the signal of both channels are rectified and then

added. This means, even if one channel signal appears

inverted to the other channel, with the TEA0678 the normal

AMS function is ensured (see Figs 4, 5 and 6).

Equalization time constant switching (70

µs or 120 µs)

is achieved when pin AMSEQ is connected to GND via an

18 k

Ω resistor (120 µs), or left open-circuit (70 µs).

This does not affect the AMS output signal during AMS

mode (see Fig.1).

Head switching is achieved when pin HS is connected to

GND (input IN1 active) or connected to HIGH (5 V) level

(input IN2 active). If left open-circuit IN1 is active.

Mute is enabled when pin MUTE is connected to ground

and off when connected to HIGH (5 V) level. For smooth

switching a time constant is recommended. If left

open-circuit MUTE is active.

The differential output stage of each channel is

connected via a provision to the Dolby and pre-amplifier

part. This provision may be used for any processing of the

tape signal or to add another signal. Each output drives a

resistive load of nominal 10 k

Ω and is capable of driving

1k

Ω, also a capacitive load of 1.2 nF to ground and

between differential outputs. Each output can be

short-circuited to a battery (16 V) via a coupling capacitor

(4.7

µF).

LIMITING VALUES

In accordance with the Absolute Maximum Rating System (IEC 134); note1.

Notes

1. The device may not operate correctly when subjected to these ratings when the ratings exceed the electrical

characteristics of the device as specified in Chapter “Characteristics”. The device will recover automatically when the

environment is reduced to the requirements of the characteristics.

maximum input voltage of 6.5 V for the switching input pins.

3. Human body model (1.5 k

Ω, 100 pF).

4. Machine model (0

Ω, 200 pF).

SYMBOL

PARAMETER

CONDITIONS

MIN.

MAX.

UNIT

supply voltage

0

16

V

−0.3

V

input voltage at pin 3 (NR/AMS), pin 18 (HS) and

pin 30 (MUTE)

note 2

−0.3

+6.5

V

−

5s

storage temperature

−55

+150

°C

operating ambient temperature

−40

+85

°C

electrostatic handling voltage for all pins

note 3

−2+2

kV

note 4

−500

+500

V