wm2002 Wolfson Microelectronics plc, wm2002 Datasheet - Page 7

• Manufacturer Part Number: wm2002
• Description: Stereo Headphone Driver With Wolfson Myzonetm Ambient Noise Cancellation
• Manufacturer: Wolfson Microelectronics plc

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TYPICAL APPLICATIONS
Figure 1 Typical Application
WOLFSON MYZONE
w
Noise Cancelling Input
(ANC microphones)
Line Input (audio source)
Line Input (audio source)
MICBIAS
MICVDD
MICRN
MICLN
MICRP
MICLP
INLN
INLP
INLN
INLP
A typical application circuit is illustrated in Figure 1, showing the line inputs, ANC microphone inputs,
and stereo headphone output.
The Wolfson myZone
using destructive interference to reduce the acoustic energy of the ambient sound.
The ANC engine is configured using parameters that are determined during product development
and programmed on integrated OTP memory. The configuration settings are specific to the acoustic
properties of the target application. The primary acoustic elements in an application are typically the
microphones and the speaker, but other components such as the plastics and the PCBs also have
significant importance to the acoustic coefficient data.
Note that the WM2002 configuration parameters are determined during development and are
programmed in the OTP memory during production calibration. These parameters are application-
specific, and must be recalculated following any change in the design of the acoustic elements of
that application. Any mismatch between the acoustic coefficient data and the target application will
give inferior ANC performance.
The ANC engine employs digital circuits to process the ambient noise (microphone) signals; these
inputs are digitized by two Analogue to Digital Converters (ADCs), then filtered and processed in
accordance with the acoustic parameters programmed into the WM2002. The noise cancellation
signals are then output via two Digital to Analogue Converters (DACs) and mixed with the received
voice or audio playback (line) signals.
The ANC engine can support multiple noise cancellation filter coefficients, to enable best
performance under different ambient noise conditions and different audio playback conditions. Other
user-selectable options are also available, such as mute/talk-through modes.
Noise cancellation is applied selectively to different audio frequency bands; a low frequency limiter
ensures that the ANC algorithms deliver noise reduction in the most sensitive frequency bands,
without introducing distortion in other frequency bands.
The ANC engine is adaptive to different ambient noise levels in order to provide the most natural
sound at the headphone audio output. It also incorporates a noise gating function, which ensures that
the noise cancellation performance is optimised across a wide range of input signal conditions.
TM
WM2002
AMBIENT NOISE CANCELLATION (ANC)
VMID
VMID
VMID
VMID
and Microphone Bias
Analogue Reference
M
U
X
M
U
X
M
U
X
M
U
X
Line PGA
-6dB to +6dB in 1dB steps
Mic PGA
-6dB to +30dB in 1dB steps
Mic PGA
-6dB to +30dB in 1dB steps
Line PGA
-6dB to +6dB in 1dB steps
+
+
+
+
-
-
-
-
LED driver
ADC L
ADC L
TM
(ANC) engine within the WM2002 improves the intelligibility of a voice call by
Digital Microphone Interface
CANCELLATION
AMBIENT NOISE
Sequencer
Control
TM
Control Interface
Memory
OTP
DAC L
DAC R
LDO Regulators
Suppression
Pop & Click
reference
Bandgap
Product Brief, August 2010, Rev 1.1
-1
-1
Oscillator
Charge Pump
DC-DC Boost
Converter
VREF
M
U
X
BATTVDD
CPVOUT
CPGND
CFB2
CFB1
HPOUTLP
HPOUTLN
HPOUTRP
HPOUTRN
HPGND
Stereo Headphone
WM2002
7