WM8950 datasheet(12/52 Pages) WOLFSON

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WM8950

Preliminary Technical Data

PTD Rev 2.1 June 2005

DEVICE DESCRIPTION

INTRODUCTION

The WM8950 is a low power audio ADC, with flexible line and microphone input. Applications for this

device include games console accessories, digital still cameras, voice recorders and other general

purpose audio applications.

FEATURES

The chip offers great flexibility in use, and so can support many different modes of operation as

follows:

MICROPHONE INPUTS

Microphone inputs are provided, allowing for either a differential microphone input or a single ended

microphone to be connected.

These inputs have a user programmable gain range of -12dB to

+35.25dB using internal resistors. After the input PGA stage comes a boost stage which can add a

further 20dB of gain. A microphone bias is output from the chip which can be used to bias the

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.

AUX INPUT

The device includes a mono input, AUX, that can be used as an input for warning tones (beep) etc.

This path can also be summed into the input in a flexible fashion, either to the input PGA as a

second microphone input or as a line input. The configuration of this circuit, with integrated on-chip

resistors allows several analogue signals to be summed into the single AUX input if required.

ADC

The mono ADC uses a multi-bit high-order oversampling architecture to deliver optimum

performance with low power consumption. Various sample rates are supported, from the 8ks/s rate

typically used in voice dictation, up to the 48ks/s rate used in high quality audio applications.

DIGITAL FILTERING

Advanced Sigma Delta Converters are used along with digital decimation and interpolation filters to

give high quality audio at sample rates from 8ks/s to 48ks/s.

Application specific digital filters are also available which help to reduce the effect of specific noise

sources such as ‘wind noise’. The filters include a programmable ADC high pass filter, an IIR filter

with fully programmable coefficients, and a 5-band equaliser that can be applied to the record path in

order to improve the overall audio sound from the device.

AUDIO INTERFACES

The WM8950 has a standard audio interface, to support the transmission of audio data from the

chip. This interface is a 4 wire standard audio interface which supports a number of audio data

formats including I

2S, DSP Mode, MSB-First, left justified and MSB-First, right justified, and can

operate in master or slave modes.

CONTROL INTERFACES

To allow full software control over all its features, the WM8950 offers a choice of 2 or 3 wire MPU

control interface. It is fully compatible and an ideal partner for a wide range of industry standard

microprocessors, controllers and DSPs. The selection between 2-wire mode and 3-wire mode is

determined by the state of the MODE pin. If MODE is high then 3-wire control mode is selected, if

MODE is low then 2-wire control mode is selected.

In 2 wire mode, only slave operation is supported, and the address of the device is fixed as 0011010.

CLOCKING SCHEMES

WM8950 offers the normal audio clocking scheme operation, where 256fs MCLK is provided to the

ADC.

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