
WM8731
Portable Internet Audio CODEC with
Headphone Driver and Programmable Sample Rates
Advanced Information, Rev 2.0, February 2001
WOLFSON MICROELECTRONICS LTD
Lutton Court, Bernard Terrace, Edinburgh, EH8 9NX, UK
Tel: +44 (0) 131 667 9386
Fax: +44 (0) 131 667 5176
Email: sales@wolfson.co.uk
www.wolfsonmicro.com
Advanced Information
data sheets
contain preliminary data on new products
in the preproduction phase of
development. Supplementary data will be
published at a later date.
2001 Wolfson Microelectronics Ltd
.
DESCRIPTION
The WM8731 is a low power stereo CODEC with an
integrated headphone driver. It offers the user the unique
ability to independently program the ADC and DAC sample
rates from a single clock source. The WM8731 is designed
specifically for portable MP3 audio and speech players and
recorders. The WM8731 is also ideal for MD, CD-RW
machines and DAT recorders.
Stereo line and mono microphone level audio inputs are
provided, along with a mute function, programmable line
level volume control and a bias voltage output suitable for
an electret type microphone.
Stereo 24-bit multi-bit sigma delta ADCs and DACs are
used with oversampling digital interpolation and decimation
filters. Digital audio input word lengths from 16-32 bits and
sampling rates from 8kHz to 96kHz are supported.
Stereo audio outputs are buffered for driving headphones
from a programmable volume control, line level outputs are
also provided along with anti-thump mute and power
up/down circuitry.
The device is controlled via a 2 or 3 wire serial interface.
The interface provides access to all features including
volume controls, mutes, de-emphasis and extensive power
management facilities. The device is available in a small 28-
pin SSOP package.
FEATURES
Audio Performance
97dB SNR (‘A’ weighted @ 48kHz) ADC
100dB SNR (‘A’ weighted @ 48kHz) DAC
1.42 – 3.6V Digital Supply Operation
2.7 – 3.6V Analogue Supply Operation
ADC and DAC Sampling Frequency: 8kHz – 96kHz
Selectable ADC High Pass Filter
2 or 3-Wire MPU Serial Control Interface
Programmable Audio Data Interface Modes
I
2
S, Left, Right Justified or DSP
16/20/24/32 bit Word Lengths
Master or Slave Clocking Mode
Stereo Audio Inputs and Outputs
Microphone Input and Electret Bias with Side Tone Mixer
Input and Output Volume and Mute Controls
Highly Efficient Headphone Driver
Playback Mode Power Consumption < 18mW
Analogue Pass Through Power Consumption < 9mW
28-Pin SSOP Package
APPLICATIONS
Portable MP3 Players and Recorders
CD and Minidisc Recorders
BLOCK DIAGRAM
MUX
MUX
VOL
VOL
ADC
ADC
DIGITAL
FILTERS
DIGTAL AUDIO INTERFACE
CONTROL INTERFACE
DAC
DAC
VOL/
MUTE
VOL/
MUTE
H/P
DRIVER
H/P
DRIVER
C
S
S
Σ
Σ
RHPOUT
LHPOUT
ROUT
LOUT
RLINEIN
LLINEIN
VMID
D
(
D
AVDD
AGND
0dB/
20dB
MICIN
+12 to -34.5dB,
1.5dB Steps
C
+6 to -73dB
1 dB Steps
HPVDD
HPGND
+6 to -73dB
1 dB Steps
+12 to -34.5dB,
1.5dB Steps
D
(
A
D
B
D
A
OSC
X
X
M
MICBIAS
MUTE
Bypass
Bypass
Side Tone
Side Tone
CLKIN
DIVIDER
(Div x1, x2)
CLKOUT
DIVIDER
(Div x1, x2)
ATTEN/
MUTE
MUTE
MUTE
ATTEN/
MUTE
MUTE
MUTE
MUTE
MUTE
MUTE
WM8731