LM1971

Digitally Controlled 62 dB Audio Attenuator with/Mute

General Description

The LM1971 is a digitally controlled single channel audio at-

tenuator fabricated on a CMOS process. Attenuation is vari-

able in 1 dB steps from 0 dB to −62 dB. A mute function dis-

connects the input from the output, providing over 100 dB of

attenuation.

The performance of the device is exhibited by its ability to

change attenuation levels without audible clicks or pops. In

addition, the LM1971 features a low Total Harmonic Distor-

tion (THD) of 0.0008%, and a Dynamic Range of 115 dB,

making it suitable for digital audio needs. The LM1971 is

available in both 8-pin plastic DIP or SO packages.

The LM1971 is controlled by a TTL/CMOS compatible 3-wire

serial digital interface. The active low LOAD line enables the

data input registers while the CLOCK line provides system

timing. Its DATA pin receives serial data on the rising edge of

each CLOCK pulse, allowing the desired attenuation setting

to be selected.

Key Specifications

n Total harmonic distortion

0.0008% (typ)

n Frequency response

n Attenuation range (excluding mute)

62 dB (typ)

n Dynamic range

115 dB (typ)

n Mute attenuation

102 dB (typ)

Features

n 3-wire serial interface

n Mute function

n Click and pop free attenuation changes

n 8-pin plastic DIP and SO packages available

Applications

n Communication systems

n Cellular Phones and Pagers

n Personal computer audio control

n Electronic music (MIDI)

n Sound reinforcement systems

n Audio mixing automation

Typical Application

DS012353-1

FIGURE 1. Typical Audio Attenuator Application Circuit

May 1999

© 1999 National Semiconductor Corporation

DS012353

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