AS3421 Datasheet, PDF (1/61 Pages) ams AG – Low Power Ambient Noise-Cancel l ing Speaker Dr iver

Datasheet
AS3421 AS3422
Low Power Ambient Noise-Cancelling Speaker Driver
1 General Description
The AS3421/22 are speaker driver with Ambient Noise Cancelling
function for headsets, headphones or ear pieces. It is intended to
improve quality of e.g. music listening, a phone conversation etc. by
reducing background ambient noise.
The fully analog implementation allows the lowest power
consumption, lowest system BOM cost and most natural received
voice enhancement otherwise difficult to achieve with DSP
implementations. The device is designed to be easily applied to
existing architectures.
An internal OTP-ROM can be optionally used to store the
microphone gain calibration settings as well as all application
specific settings.
The AS3421/22 can be used in different configurations for best
trade-off of noise cancellation, required filtering functions and
mechanical designs.
The simpler feed-forward topology is used to effectively reduce
frequencies typically up to 2-3kHz. The feed-back topology with
either 1 or 2 filtering stages has it strengths especially at very low
frequencies. The typical bandwidth for feedback system is from 20Hz
up to 1kHz which is a little bit lower than with feed forward systems.
The filter loop for both systems is determined by measurements, for
each specific headset individually, and depends very much on
mechanical designs. The gain and phase compensation filter
network is implemented with cheap resistors and capacitors for
lowest system costs.
AS3421/22 features also an audio playback only mode which allows
the user to easily switch between ANC on and off mode. In ANC off
mode unused blocks are automatically switch off to guaranty lowest
power consumption in each operating mode.
2 Key Features
Microphone Input
128 gain steps @ 0.375dB and MUTE with AGC
Differential, low noise microphone amplifier
Single ended or differential mode
Improved supply for electret microphone
MIC gain OTP programmable
High Efficiency Headphone Amplifier
2x23mW, 0.1% THD+N @ 32Ω, 1.5V supply,
100dB SNR
Bridged mode for e.g. 300Ω loads
Click and pop less start-up and mode switching
Line Input
Volume control via serial interface or push buttons
64 steps @ 0.75dB and MUTE, pop-free gain setting
Fully differential stereo line inputs
ANC processing
Feed-forward cancellation
Feed-back cancellation with filter loop transfer function
definable via simple RC components
Simple in production SW calibration
12-30dB noise reduction (headset dependent)
10-3000Hz wide frequency active noise attenuation (headset
dependent)
Monitor Function
For assisted hearing, i.e. to monitor announcements
Fixed (OTP prog.) ambient sound amplification to compensate
headphone passive attenuation
Incremental Functions
ANC with or without music on the receiving path
Music Playback mode for lowest power consumption
OTP ROM for automatic trimming during production (4 times
programmable)
Performance Parameter
7mA @ 1.5V stereo ANC; <1µA quiescent
Extended PSRR for 217Hz
Increased TDMA noise immunity
Interfaces
2-wire serial control mode & volume inputs
Calibration via Line-In or 2-wire serial interface
Fixed 1.0-1.8V supply with internal CP
Package
AS3421 QFN24 [4x4mm] 0.5mm pitch
AS3422 QFN32 [5x5mm] 0.5mm pitch
3 Applications
The devices are ideal for wireless devices like stereo Bluetooth
headsets as well as stereo wireless headsets.
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Revision 0.90
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