Pre-Production
WM8985
DEVICE DESCRIPTION
INTRODUCTION
The WM8985 is a low power audio codec combining a high quality stereo audio DAC and ADC, with
flexible line and microphone input and output processing.
FEATURES
The chip offers great flexibility in use, and so can support many different modes of operation as
follows:
MICROPHONE INPUTS
Two pairs of stereo microphone inputs are provided, allowing a pair of stereo microphones to be
pseudo-differentially connected, with user defined gain. The provision of the common mode input pin
for each stereo input allows for rejection of common mode noise on the microphone inputs (level
depends on gain setting chosen). A microphone bias is output from the chip which can be used to
bias both microphones. The signal routing can be configured to allow manual adjustment of mic
levels, or to allow the ALC loop to control the level of mic signal that is transmitted.
Total gain through the microphone paths of up to +55.25dB can be selected.
PGA AND ALC OPERATION
A programmable gain amplifier is provided in the input path to the ADC. This may be used manually
or in conjunction with a mixed analogue/digital automatic level control (ALC) which keeps the
recording volume constant.
AUXILIARY ANALOG LINE INPUTS (AUXL, AUXR)
The inputs, AUXL and AUXR, can be used as a stereo line input or as an input for warning tones (or
‘beeps’) etc. These inputs can be summed into the record paths, along with the microphone preamp
outputs, so allowing for mixing of audio with ‘backing music’ etc as required.
Additional stereo analog signals might be connected to the Line inputs of WM8985 (e.g. melody chip
or FM radio), and the stereo signal listened to via headphones, or recorded, simultaneously if
required.
ADC
The stereo ADC uses a 24-bit high-order over sampling architecture to deliver optimum performance
with low power consumption.
HI-FI DAC
The hi-fi DAC provides high quality audio playback suitable for all portable audio hi-fi type
applications, including MP3 players and portable disc players of all types.
OUTPUT MIXERS
Flexible mixing is provided on the outputs of the device. A stereo mixer is provided for the stereo
headphone or line outputs, LOUT1/ROUT1, and additional summers on the OUT3/OUT4 outputs
allow for an optional differential or stereo line output on these pins. Gain adjustment PGAs are
provided for the LOUT1/ROUT1 and LOUT2/ROUT2 outputs, and signal switching is provided to
allow for all possible signal combinations.
PP, Rev 3.4, October 2006
27
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
