Noise cancelling headphone speaker driver cuts costs in tiny packaging

March 17, 2016 // By Graham Prophet
ams’ cost-effective AS3412 opens up, the company says, mass market opportunities for active noise cancellation, such as in the bundled head-sets supplied with smartphones, bringing ANC to this price-point for the first time.

The device extends the ams family of ANC speaker drivers, drawing on the analogue noise cancellation technology developed by ams and in use by many audio equipment manufacturers.

The AS3412 offers typical noise cancellation performance of up to 30dB of external noise attenuation over an audible frequency range of 20 Hz – 2 kHz. A highly integrated solution, the AS3412 combines its ANC circuitry with a speaker driver, capable of driving 2 x 34 mW into a 32 Ω load, in a 2.2 x 2.2 x 0.4 mm chip-scale package. Operating from a 1.6V-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 inter-faces.

 

Supported by a development kit including a software GUI, firmware and simulation environment, 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 bill-of-materials 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.

 

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

 

The audio performance provided by the speaker driver function of the AS3412 is suited to headsets used with