WM8976 datasheet(20/108 Pages) WOLFSON

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WM8976

Pre-Production

PP Rev 3.0 April 2006

OUT3 and OUT4 can be configured to provide an additional stereo lineout from the output of the

DACs, the mixers or the input microphone boost stages. Alternatively OUT4 can be configured as a

mono mix of left and right DACs or mixers, or simply a buffered version of the chip midrail reference

voltage. OUT3 can also be configured as a buffered VMID output. This voltage may then be used as

a headphone ‘pseudo ground’ allowing removal of the large AC coupling capacitors often used in the

output path.

AUDIO INTERFACES

The WM8976 has a standard audio interface, to support the transmission of data to and from the

chip. This interface is a 3 wire standard audio interface which supports a number of audio data

formats including I2S, DSP/PCM Mode (a burst mode in which LRC sync plus 2 data packed words

are transmitted), 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 features, the WM8976 offers a choice of 2 or 3 wire control

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

microprocessors, controllers and DSPs.

Selection between the modes is via the MODE pin. In 2 wire mode the address of the device is fixed

as 0011010.

CLOCKING SCHEMES

WM8976 offers the normal audio DAC clocking scheme operation, where 256fs MCLK is provided to

the DAC and ADC.

A PLL is included which may be used to generate these clocks in the event that they are not

available from the system controller. This PLL uses an input clock, typically the 12MHz USB or ilink

clock, to generate high quality audio clocks. If this PLL is not required for generation of these clocks,

it can be reconfigured to generate alternative clocks which may then be output on the GPIO pins and

used elsewhere in the system.

POWER CONTROL

The design of the WM8976 has given much attention to power consumption without compromising

performance. It operates at very low voltages, and includes the ability to power off any unused parts

of the circuitry under software control, and includes standby and power off modes.

OPERATION SCENARIOS

Flexibility in the design of the WM8976 allows for a wide range of operational scenarios, some of

which are proposed below:

Multimedia phone; High quality playback to a stereo headset, a mono ear speaker or a loudspeaker

is supported, allowing Hi-Fi playback to be mixed with voice and other analogue inputs while

simultaneously transmitting a differential output from the microphone amplifier. A 5-band EQ enables

Hi-Fi playback to be customised to suit the user's preferences and the music style, while

programmable filtering allows fixed-frequency noise (e.g. 217Hz) to be reduced in the digital domain.

Camcorder; The provision of a microphone preamplifier allows support for both internal or external

microphones. All drivers for speaker, headphone and line output connections are integrated. The

selectable ‘application filters’ after the ADC provide for features such as ‘wind noise’ reduction, or

mechanical noise reducing filters.

Digital still camera recording; Support for digital recording is similar to the camcorder case. But

additionally if the DSC supports MP3 playback, and perhaps recording, the ability of the ADC to

support full 48ks/s high quality recording increases device flexibility.

AUXILIARY ANALOGUE INPUTS

An analogue stereo FM tuner or other auxiliary analogue input can be connected to the AUX inputs of

WM8976, and the stereo signal listened to via headphones.

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