WM8945
Production Data
DEVICE DESCRIPTION
INTRODUCTION
The WM8945 is a highly integrated low power hi-fi CODEC designed for portable devices such as
digital still cameras and multimedia phones. Flexible analogue interfaces and powerful digital signal
processing (DSP) in a 2.96 x 3.06mm footprint make it ideal for small portable devices.
The WM8945 supports up to 4 analogue audio inputs. One single-ended or pseudo differential
microphone / line input is selected as the ADC input source. The two auxiliary inputs can be selected
as line inputs to the ADC, or as direct signal paths to the output mixers. An integrated bias reference
is provided to power standard electret microphones. A digital microphone interface is also supported,
with direct input to the DSP core via the ADC.
The hi-fi ADC and DAC operate at sample rates from 8kHz up to 48kHz. A high pass filter is available
in the ADC path for removing DC offsets and suppressing low frequency noise such as mechanical
vibration and wind noise. A digital tone (‘beep’) generator allows audio tones to be injected into the
DAC output path.
The WM8945 provides a powerful DSP capability for configurable filtering and processing of the
digital audio path. The DSP provides low-pass / high-pass filtering, notch filters, 5-band EQ, dynamic
range control and a programmable DF1 digital filter. The tuned notch filters allow narrow frequency
bands to be attenuated, to provide filtering of motor noise or other unwanted sounds; the 5-band EQ
allows the signal to be adjusted for user-preferences. The dynamic range control provides a range of
compression, limiting and noise gate functions to support optimum configuration for recording or
playback modes. The DF1 filter allows user-specified algorithms to be implemented in the digital
signal chain.
The Wolfson ReTune™ feature is a highly-configurable DSP algorithm which can be tailored to cancel
or compensate for imperfect characteristics of the housing, loudspeaker or microphone components
in the target application. The ReTune™ algorithm coefficients and register contents are calculated
using Wolfson’s WISCE™ software; lab bench tests and audio reference measurements must be
performed in order to determine the optimum settings.
The digital signal routing between the ADC, DAC and I2S digital audio interface can be configured in
different ways according to the application requirements. The DSP functions may be applied to the
ADC record path, or the DAC playback path.
Three analogue output mixers are provided, connected to 3 analogue output pins. A mono line output
and mono BTL headphone/speaker may be connected to these outputs.
The WM8945 incorporates an LDO regulator for compatibility with a wide range of supply rails; the
internal LDO can also reduce any interference resulting from a noisy supply rail. The LDO regulator
can also be used to provide a regulated supply voltage to other circuits.
I2C or SPI control interface modes for read/write access to the register map. A single external clock
provides timing reference for all the digital functions; an integrated Frequency Locked Loop (FLL) also
provides flexibility to perform frequency conversions and to remove noise/jitter from the external
clock. The FLL can be configured for reduced power consumption, or for different filtering
requirements of the reference source.
Additional functions include a 4-wire controller for interface to standard resistive touch panels, a 12-bit
auxiliary ADC for DC measurement / battery monitoring, and also a current-mode video buffer
providing excellent video signal reproduction at low operating voltages. Up to 4 GPIO pins may be
configured for miscellaneous input/output, or for status indications from the Touch panel, AUXADC or
temperature monitoring functions.
PD, May 2011, Rev 4.1
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
