WM8978GEFLSLASHV datasheet(15/78 Pages) WOLFSON

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WM8978

PP Rev 1.7 January 2005

DEVICE DESCRIPTION

INTRODUCTION

The WM8978 is a low power audio codec combining a high quality stereo audio DAC and ADC, with

flexible line and microphone input and output processing. Applications for this device include stereo

digital camcorders, and digital still cameras with either mono or stereo record and playback

capability.

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 for a pair of stereo microphones to be

pseudo-differentially connected, with user defined gain using internal resistors. 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 indeed 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.

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.

ADC

The stereo ADC uses a multi-bit high-order 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.

WM8978GEFL/V Datasheet(PDF) 15 Page - Wolfson Microelectronics plc

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