AMS AS3501 EB

The AS3500/01/02 is a speaker driver with ambient noise cancellation for mobile phones, headsets, or earphones. It is designed to improve the quality of applications such as music listening and phone calls by reducing background ambient noise. The fully analog implementation achieves minimum power consumption, lowest system BOM cost, and the most natural received voice enhancement — qualities that DSP-based implementations struggle to match. The device is designed for easy integration into existing architectures. An internal OTP-ROM can optionally be used to store microphone gain calibration settings. The AS3500/01/02 supports multiple configurations to achieve the optimal balance between noise cancellation, required filtering functionality, and mechanical design. A simpler feedforward topology is used to effectively reduce low-frequency background noise. Feedback topologies with 1 or 2 filter stages can be used to reduce noise over a wider frequency range, and can even realize transfer functions such as speaker equalization, Baxandall equalization, high/low shelf filters, as well as set a predefined loop bandwidth. Users can optimize the filter loop for the electrical and mechanical design of a specific mobile phone by sizing simple resistor (R) and capacitor (C) components. Most mobile phone implementations will use a single noise-sensing microphone. Two microphones can be used to increase placement flexibility within the mechanical design of the phone. Bridge mode can even be used to drive high-impedance headphones.

• Microphone input: 128-step gain, 0.375dB per step, with AGC and mute; differential, low-noise microphone amplifier; single-ended or differential mode; electret microphone bias supply; microphone gain configurable via OTP.
• High-efficiency headphone amplifier: 2×34mW output power at 1.5V supply into 16Ω load, THD 0.1%, SNR 100dB; bridge mode for loads such as 300Ω; click- and pop-free startup and mode switching.
• Line input: volume control via serial interface or volume pin; 64 steps, 0.75dB per step, with mute and pop-free gain setting; single-ended stereo or mono differential mode.
• ANC processing: feedforward noise cancellation; feedback noise cancellation with loop transfer function defined by simple RC components; simple software calibration in production; 12–30dB noise reduction (headphone-dependent); 10–2000Hz broadband active noise attenuation (headphone-dependent).
• Monitor function: for hearing assistance, i.e., monitoring announcements; fixed (OTP-programmable) ambient sound amplification to compensate for passive headphone attenuation; volume-controllable ambient sound amplification mixed with line input at fixed (OTP-programmable) attenuation.
• Incremental features: ANC with or without music on the receive path; improved dynamic range playback; simple, low-cost single noise-sensing microphone implementation; OTP ROM for automatic fine-tuning during production.
• Performance: 5/3.8mA current in stereo/mono ANC mode at 1.5V supply; standby current below 1μA; enhanced PSRR at 217Hz.
• Interface: 2-wire serial control mode and volume input; calibration via line input or 2-wire serial interface; single-cell battery or fixed 1.0–1.8V supply with internal CP.
• Package: AS3500, AS3501 in QFN24 [4×4mm], 0.5mm pitch; AS3502 in QFN32 [5×5mm], 0.5mm pitch.

Earphones, headphones, hands-free kits, mobile phones, voice communication devices