As a growing number of countries adopt legislation that prohibits the use of handheld mobile phones while driving, demand for hands-free kits and wireless headsets is on the rise. The challenging sound environment within automobiles, however, places an increased burden on the audio processing systems within those devices. And with mobile phone users struggling to hear and be heard in noisy environments, system designers are working hard to integrate more-advanced audio processing into portable audio devices.
Mobile products must accomplish these tasks in smaller form factors with better battery life, as well as with echo cancellation and noise suppression functionality. Analog IC makers such as Analog Devices, Maxim Integrated Products, National Semiconductor, Texas Instruments and On Semiconductor are responding with audio chips that improve sound quality by driving louder volume from speakers and removing the output frequency distortions common with DSP- or microprocessor-software-based systems.
One technique is to use a boost converter to drive higher output power. In May, TI (Dallas) rolled the TPA2014D1, which provides output drive capability of up to 1.5 watts per channel across an 8-ohm load, ensuring that volume is maintained even when the battery discharges to its minimum voltage.
TI has also fielded the TPA2016D2, which provides a 1.7-W drive capability across an 8-ohm load. TI said the Class-D amplifier is the first stereo device to incorporate dynamic range compression for automatically adjusting the audio to the desired loudness range while protecting the speaker and preventing clipping and distortion.
On Semiconductor (Phoenix) recently announced the latest member in its BelaSigna family of audio processors, formerly offered by AMI Semiconductor. Marketed under the brand name BelaSigna 300, the high-fidelity audio processors target portable communication devices. The dual-core architecture lets multiple advanced audio algorithms, such as echo cancellation and noise reduction, run simultaneously while maintaining ultralow power consumption. A 24-bit open-programmable DSP core and a configurable accelerator signal processing engine deliver the flexibility of a generic DSP with the power consumption and size of a fixed-function ASIC, On Semi said. Advanced analog audio inputs, combined with the 24-bit signal path, boost audio quality.
Claiming to have lowered the bar for power consumption, National Semiconductor Corp. (Santa Clara, Calif.) has brought out the first device in a line of audio products incorporating far-field noise suppression technology. The technology delivers more natural-sounding voice quality by eliminating the output-frequency distortions and other audio artifacts common with DSP- or microprocessor-software-based systems that use subband frequency processing algorithms to implement noise suppression.
National's PowerWise LMV1088 dual-input microphone array amplifier reduces background noise and improves voice communication clarity in mobile phones, two-way radios and powered headsets. It consumes one-tenth the power (1 mA) of comparable DSP- or microprocessor-software-based systems.
As speaker apps become more compact, stereophonic sound quality is jeopardized. The 3-D stereo enhancement in the MAX9775 from Maxim Integrated Products emulates stereo sound in situations where the speakers must be positioned close together. Wave interference cancels the left channel in the vicinity of the listener's right ear and vice versa, yielding an “apparent” separation between the speakers that is a factor of four or greater than the actual physical separation, Maxim said.
The part integrates a mono 80-mW DirectDrive receiver amplifier, a stereo 80-mW Direct-Drive headphone amp, and a Class D stereo 1.5-W audio power amp. Maxim (Sunnyvale, Calif.) also offers the MAX9776, which provides the mono 80-mW receiver amp, the stereo 80-mW DirectDrive headphone amplifier and a mono Class D amp.
Analog Devices' SSM2317 is a fully integrated, high-efficiency Class-D audio amp. The application circuit requires a minimum of external components and operates from a single 2.5-V to 5.5-V supply. It is capable of delivering 3 W of continuous output power with less than 1percent THD + N driving a 3-ohm load from a 5.0-V supply. The SSM2317's high-efficiency, low-noise modulation scheme does not require external LC output filters. The modulation continues to provide high efficiency even at low output power. Spread-spectrum pulse density modulation provides lower EMI radiated emissions than is provided by other Class-D architectures.
Pop-and-click suppression circuitry minimizes voltage glitches at the output during turn-on and turn-off.
| A 3-D stereo enhancement function allows the MAX9775 to
widen the stereo sound field, immersing the listener in a cleaner, richer sound than is typically found in portables