环境噪音消除" title="环境噪音消除">环境噪音消除" title="环境噪音消除">环境噪音消除（ANC）功能的扬声器放大器，能降低本底环境噪音，从而提高了手持设备，耳机，语音通信设备等的音频质量。ANC处理的带宽10-2000Hz，噪音降低10-30dB，主要用于耳机，手持设备，手机，免提卡和语音通信设备。本文介绍了AS3400/10/30主要特性，反馈和正馈方框图，反馈应用案例电路图与差分正馈应用案例电路图。
The AS3400/10/30 are speaker driver with Ambient Noise Cancelling function for handsets, 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 microphones gain calibration settings.
The AS3400/10/30 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 low frequency background noise. The feed-back topology with either 1 or 2 filtering stages can be used to reduce noise for a larger frequency range, and to even implement transfer functions like speaker equalization, Baxandall equalization, high/low shelving filter and to set a predefined loop bandwidth.
The filter loop is optimized by the user for specific handset electrical and mechanical designs by dimensioning simple R, C components. Most handset implementations will make use of a single noise detecting microphone. Two microphones could be used to allow for increased flexibility of their location in the handset mechanical design. Using the bridged mode allows to even drive high impedance headsets.
AS3400/10/30主要特性：
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
?? 2x34mW, 0.1% THD @ 16Ω, 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 volume pin
?? 64 steps @ 0.75dB and MUTE, pop-free gain setting
?? Single ended stereo or mono differential mode
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)
?? 10-2000Hz 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
?? Volume controlled ambient sound amplification mixed with fixed (OTP prog.) attenuation of LineIn
Incremental Functions
?? ANC with or without music on the receiving path
?? Improved dynamic range playback
?? OTP ROM for automatic trimming during production (4 times programbable)
Performance Parameter
?? 5/3.8mA @ 1.5V stereo/mono ANC; <1μA quiescent
?? Extended PSRR for 217Hz
Interfaces
?? 2-wire serial control mode & volume inputs
?? Calibration via Line-In or 2-wire serial interface (patent pending)
?? Single cell or fixed 1.0-1.8V supply with internal CP
Package
?? AS3400, AS3410 QFN24 [4x4mm] 0.5mm pitch
?? AS3430 QFN32 [5.x5mm] 0.5mm pitch
AS3400/10/30应用：
The devices are ideal for Ear pieces, Headsets, Hands-Free Kits, Mobile Phones, and Voice Communicating Devices.
图1。AS3400反馈方框图
图2。AS3400前馈方框图
图3。AS3400前馈ANC方框图
图4。AS3430反馈应用案例电路图
图5。AS3430差分正馈应用案例电路图
详情请见：
http://www、austriamicrosystems、com/content/download/143123/756655/85634
