AS3421/22 Low Power Ambient Noise-Cancelling Speaker Driver Line Input 1 General Description Volume control via serial interface or push buttons The AS3421/22 are speaker driver with Ambient Noise Cancelling 64 steps 0.75dB and MUTE, pop-free gain setting function for headsets, headphones or ear pieces. It is intended to Fully differential stereo line inputs improve quality of e.g. music listening, a phone conversation etc. by reducing background ambient noise. ANC processing The fully analog implementation allows the lowest power Feed-forward cancellation consumption, lowest system BOM cost and most natural received voice enhancement otherwise difficult to achieve with DSP Feed-back cancellation with filter loop transfer function implementations. The device is designed to be easily applied to definable via simple RC components existing architectures. Simple in production SW calibration An internal OTP-ROM can be optionally used to store the 12-30dB noise reduction (headset dependent) microphone gain calibration settings as well as all application specific settings. 10-3000Hz wide frequency active noise attenuation (headset dependent) The AS3421/22 can be used in different configurations for best trade-off of noise cancellation, required filtering functions and Monitor Function mechanical designs. For assisted hearing, i.e. to monitor announcements The simpler feed-forward topology is used to effectively reduce Fixed (OTP prog.) ambient sound amplification to compensate frequencies typically up to 2-3kHz. The feed-back topology with headphone passive attenuation either 1 or 2 filtering stages has it strengths especially at very low frequencies. The typical bandwidth for feedback system is from 20Hz Incremental Functions up to 1kHz which is a little bit lower than with feed forward systems. ANC with or without music on the receiving path The filter loop for both systems is determined by measurements, for each specific headset individually, and depends very much on Music Playback mode for lowest power consumption mechanical designs. The gain and phase compensation filter OTP ROM for automatic trimming during production (4 times network is implemented with cheap resistors and capacitors for programmable) lowest system costs. AS3421/22 features also an audio playback only mode which allows Performance Parameter the user to easily switch between ANC on and off mode. In ANC off 7mA 1.5V stereo ANC <1A quiescent mode unused blocks are automatically switch off to guaranty lowest Extended PSRR for 217Hz power consumption in each operating mode. Increased TDMA noise immunity Interfaces 2 Key Features 2-wire serial control mode & volume inputs Microphone Input Calibration via Line-In or 2-wire serial interface 128 gain steps 0.375dB and MUTE with AGC Fixed 1.0-1.8V supply with internal CP Differential, low noise microphone amplifier Package Single ended or differential mode AS3421 QFN24 4x4mm 0.5mm pitch Improved supply for electret microphone AS3422 QFN32 5x5mm 0.5mm pitch MIC gain OTP programmable High Efficiency Headphone Amplifier 3 Applications 2x23mW, 0.1% THD+N 32, 1.5V supply, 100dB SNR The devices are ideal for wireless devices like stereo Bluetooth Bridged mode for e.g. 300 loads headsets as well as stereo wireless headsets. Click and pop less start-up and mode switching www.ams.com/ANC Revision 1.10 1 - 61AS3421/22 Datasheet - Applications Figure 1. AS3421 Feed Forward ANC Block Diagram Figure 2. AS3422 Feed-Back Block Diagram www.ams.com/ANC Revision 1.10 2 - 61