
LM1971Overture Audio Attenuator Series
Digitally Controlled 62 dB Audio Attenuator with/Mute
General Description
The LM1971 is a digitally controlled single channel audio
attenuator fabricated on a CMOS process. Attenuation is
variable in 1 dB steps from 0 dB to 62 dB. A mute function
disconnects 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
> 200 kHz (3 dB) (typ)
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
Overture is a trademark of National Semiconductor Corporation.
01235301
FIGURE 1. Typical Audio Attenuator Application Circuit
September 2002
LM1971
Overture
Audio
Attenuator
Series
Digitally
Controlled
62
dB
Audio
Attenuator
with
Mute
2002 National Semiconductor Corporation
DS012353
www.national.com