WM8994ECSSLASHR datasheet(42/363 Pages) CIRRUS

42 / 363 page

WM8994

Rev 4.6

DEVICE DESCRIPTION

INTRODUCTION

The WM8994 is a low power, high quality audio codec designed to interface with a wide range of

processors and analogue components. A high level of mixed-signal integration in a very small footprint

makes it ideal for portable applications such as mobile phones. Fully differential internal architecture

and on-chip RF noise filters ensure a very high degree of noise immunity.

The analogue circuits of the WM8994 are almost entirely backwards-compatible with the WM8993

with the exception of two additional DAC channels, a dual FLL and two integrated LDO regulators.

Three sets of audio interface pins are available in order to provide independent and fully

asynchronous connections to multiple processors, typically an application processor, baseband

processor and wireless transceiver. Any two of these interfaces can operate totally independently and

asynchronously while the third interface can be synchronised to either of the other two and can also

provide ultra low power loopback modes to support, for example, wireless headset voice calls.

Four digital microphone input channels are available to support advanced multi-microphone

applications such as noise cancellation. An integrated microphone activity monitor is available to

enable the processor to sleep during periods of microphone inactivity, saving power.

Four DAC channels are available to support use cases requiring up to four simultaneous digital audio

streams to the output drivers.

Eight highly flexible analogue inputs allow interfacing to up to four microphone inputs (single-ended or

differential), plus multiple stereo or mono line inputs. Connections to an external voice CODEC, FM

radio, line input, handset MIC and headset MIC are all fully supported. Signal routing to the output

mixers and within the CODEC has been designed for maximum flexibility to support a wide variety of

usage modes. A ‘Direct Voice’ path from a voice CODEC directly to the Speaker or Earpiece output

drivers is included.

Nine analogue output drivers are integrated, including a stereo pair of high power, high quality

Class D/AB switchable speaker drivers; these can support 2W each in stereo mode. It is also possible

to configure the speaker drivers as a mono output, giving enhanced performance. A mono earpiece

driver is provided, providing output from the output mixers or from the low-

power differential ‘Direct

Voice’ path.

One pair of ground-reference headphone outputs is provided; these are powered from an integrated

Charge Pump, enabling high quality, power efficient headphone playback without any requirement for

DC blocking capacitors. A DC Servo circuit is available for DC offset correction, thereby suppressing

pops and reducing power consumption. Four line outputs are provided, with multiple configuration

options including 4 x single-ended output or 2 x differential outputs. The line outputs are suitable for

output to a voice CODEC, an external speaker driver or line output connector. Ground loop feedback

is available on the headphone outputs and the line outputs, providing rejection of noise on the ground

connections. All outputs have integrated pop and click suppression features.

Internal differential signal routing and amplifier configurations have been optimised to provide the

highest performance and lowest possible power consumption for a wide range of usage scenarios,

including voice calls and music playback. The speaker drivers offer low leakage and high PSRR; this

enables direct connection to a Lithium battery. The speaker drivers provide eight levels of AC and DC

gain to allow output signal levels to be maximised for many commonly-used SPKVDD/AVDD1

combinations.

The ADCs and DACs are of hi-fi quality, using a 24-bit low-order oversampling architecture to deliver

optimum performance. A flexible clocking arrangement supports mixed sample rates, whilst integrated

ultra-low power dual FLLs provide additional flexibility. A high pass filter is available in all ADC and

digital MIC paths for removing DC offsets and suppressing low frequency noise such as mechanical

vibration and wind noise. A digital mixing path from the ADC or digital MICs to the DAC provides a

sidetone of enhanced quality during voice calls. DAC soft mute and un-mute is available for pop-free

music playback.

The integrated Dynamic Range Controllers (DRC) and ReTune Mobile 5-band parametric equaliser

(EQ) provide further processing capability of the digital audio paths. The DRC provides compression

and signal level control to improv

e the handling of unpredictable signal levels. ‘Anti-clip’ and ‘quick

release’ algorithms improve intelligibility in the presence of transients and impulsive noises. The EQ

provides the capability to tailor the audio path according to the frequency characteristics of an

earpiece or loudspeaker, and/or according to user preferences.

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