Speaker driver brings ANC to mass-market headphones

The AS3412 offers outstanding noise cancellation performance, typically providing up to 30dB of external noise attenuation over an audible frequency range from 20Hz to 2kHz. A highly integrated solution, the AS3412 combines its ANC circuitry with a speaker driver, capable of driving 2x34mW into a 32Ω load, in a 2.2x2.2x0.4mm chip-scale package. Operating from a 1.6-1.8V power supply, the IC is suitable for use with battery-powered equipment such as smartphones. The AS3412’s power and audio system is also compatible with USB Type-C and with Lightning interfaces.

Supported by an easy-to-use development kit including a software GUI, firmware and simulation environment, the compact AS3412 can readily be integrated into end product designs. Unlike more complex digital implementations, the AS3412 only requires a small number of supporting components, including a filter network composed of low-cost capacitors and resistors.

This means that a high-performance ANC sensor solution can be implemented with the AS3412 at a lower BOM cost than was previously possible. This enables consumer product OEMs to offer sophisticated noise-cancellation capability for the first time to users of low-cost headset and headphone products, including the bundled headsets supplied with new smartphones and media players.

An additional advantage of the AS3412 is provided by its integrated depletion-mode MOSFET, which provides a built-in bypass function. This simplifies the mechanical design of the end product by eliminating the need for a bulky bypass switch, enabling the speaker driver to continue to provide an audio output even when there is insufficient battery power remaining to support the ANC function.

The AS3412 itself draws a very low current from the battery even in noise cancellation mode. Typical power consumption in normal feed-forward operation, with a 260µA load for twin microphones, is just 11.5mW.

The audio performance provided by the speaker driver function of the AS3412 is well suited to headphones used with smartphones or media players, offering a signal-to-noise ratio of 112.5dB and a total harmonic distortion and noise figure of less than 0.01% at a music output power of 30mW.

Anna Wutke, Marketing Manager, Audio Sensors business line, ams, commented: "The experience of listening in silence to crystal-clear sound, even in a noisy environment, has in the past been enjoyed only by users of high-end headphones. With the introduction of the highly integrated AS3412, ams is now making it possible to fit ANC functionality inside a traditional hands-free headset dongle, even in low-cost headsets, to provide noise-free listening to the mass audio market."

The AS3412 ANC solution is available now in production volumes for $1.50 each in 100,000 unit quantities. An evaluation board for the AS3412 active noise cancellation speaker driver is available from the ams ICdirect online store.