NXP New TFA9911 Smart Sensing Amplifier Turns Smartphone Speaker Into Microphone, Vibration Sensor with Superior Audio Performance

March 21 2016, 03:10

NXP Semiconductors recently introduced a new smart sensing amplifier, TFA9911, featuring a high efficiency class-D audio amplifier, sophisticated speaker boost and protection, and combining speaker sensing and processing algorithms to optimize recording and calling experiences. The device transforms speaker into a microphone and features vibration detection, which enables development of new “tap” activating use cases for smartphones.

The new NXP TFA9911 features new speaker protection algorithms to increase loudness while maintaining the audio quality at speaker limit capability. It also allows Speaker-as-a-Microphone (SaM) applications using earpiece or back speaker as additional microphones for excellent performance in loud and windy environments, and Speaker-as-a-Vibration-Sensor (SaV), using a speaker as vibration sensor for tap detection.

The new amplifier provides smartphones with superior audio performance in noisy environments such as concerts or sporting events and enables loud and clear playback without saturating or distorting the sound. The new NXP device utilizes its speakers as microphones to improve the smartphone’s recording quality. Also, the amplifier equips smartphones with a vibration sensor for reliable “tap” detection on both sides of the phone, allowing users, for instance, to tap their finger on the back of the phone to take a “selfie” with a single hand. Apart from smartphones, target applications for the TFA9911 may include tablets, Portable Navigation Devices (PND), notebook computers, portable media players and small audio systems

The TFA9911 is the combination of a high efficiency class-D audio amplifier with a sophisticated speaker boost and protection algorithm, and state-of-the-art audio processing software for noise suppression and audio zooming. It can deliver 7.2 W peak output power into an 8 Ω speaker at a supply voltage of 3.6 V. The internal boost converter raises the supply voltage to 9.5 V, providing ample headroom for major improvements in sound quality.

A safe working environment is provided for the speaker under all operating conditions. The TFA9911 maximizes acoustic output while ensuring diaphragm displacement and voice coil temperature do not exceed their rated limits. This function is based on a speaker box model that operates in all loudspeaker environments (e.g. free air, closed box or vented box). Furthermore, advanced signal processing ensures the quality of the audio signal is never degraded by unwanted clipping or distortion in the amplifier or speaker. An integrated Dynamic Range Compressor (DRC) allows the speaker to operate at the highest possible power rating without suffering physical damage.

According to NXP, unlike competing solutions, the adaptive sound maximizer algorithm uses feedback to accurately calculate both the temperature and the excursion, allowing the TFA9911 to adapt to changes in the acoustic environment. Also, internal intelligent DC-to-DC conversion boosts the supply rail to provide additional headroom and power output. The supply voltage is only raised when necessary. This maximizes the output power of the class-D audio amplifier while limiting quiescent power consumption.

The TFA9911 also features a Speaker-as-Microphone function allowing the speaker to be used as a dynamic microphone when it’s not playing back audio. This feature provides best performances in high sound pressure environments like concerts. The included LifeVibes AudioCapture host software processes both speaker and microphone audio enabling high quality audio capture (music, speech…) during camcording, meetings or other recordings.

The TFA9911 also incorporates advanced battery protection. By limiting the supply current when the battery voltage is low, it prevents the audio system from drawing excessive load currents from the battery, which could cause a system undervoltage. The advanced processor minimizes the impact of a falling battery voltage on the audio quality by preventing distortion as the battery discharges.

The device features low RF susceptibility because it has a digital input interface that is insensitive to clock jitter. The second order closed loop architecture used in a class-D audio amplifier provides excellent audio performance and high supply voltage ripple rejection. The audio input interface is I²S and the control settings are communicated via an I²C-bus interface.

The device also provides the speaker with robust protection against ESD damage. In a typical application, no additional components are needed to withstand a 15 kV discharge on the speaker. The TFA9911 is available in a 49-bump WLCSP (Wafer Level Chip-Size Package) with a 400 μm pitch. Evaluation kits and other support tools are already available.

Application design tools are available for the TFA9911 in combination with the Maximus smart amplifier and LifeVibes audio processing software.
More about LifeVibes AudioCapture.
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