Pre-Production
WM8976
DEVICE DESCRIPTION
INTRODUCTION
The WM8976 is a low power audio CODEC combining a high quality stereo audio DAC and mono
ADC, with flexible line and microphone input and output processing. Applications for this device
include multimedia phones, digital camcorders, and digital still cameras with record and playback
capability.
FEATURES
The chip offers great flexibility in use, and so can support many different modes of operation as
follows:
MICROPHONE INPUT
A microphone input is provided, allowing a microphone to be pseudo-differentially connected, with
user defined gain using internal resistors. The provision of the common mode input pin allows for
rejection of common mode noise on the microphone input (level depends on gain setting chosen). A
microphone bias is output from the chip which can be used to bias the microphone. The signal
routing can be configured to allow manual adjustment of mic level, or to allow the ALC loop to control
the level of mic signal that is transmitted.
Total gain through the microphone path 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.
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. The left input can be summed into the record path, along with the microphone preamp
output, so allowing for mixing of audio with ‘backing music’ etc as required.
ADC
The ADC uses a 24-bit delta sigma oversampling 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. The output buffers can be configured in several ways,
allowing support of up to three sets of external transducers; ie stereo headphone, BTL speaker, and
BTL earpiece may be connected simultaneously. Thermal implications should be considered before
simultaneous full power operation of all outputs is attempted.
Alternatively, if a speaker output is not required, the LOUT2 and ROUT2 pins might be used as a
stereo headphone driver, (disable output invert buffer on ROUT2). In that case two sets of
headphones might be driven, or the LOUT2 and ROUT2 pins used as a line output driver.
PP Rev 3.0 April 2006
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
