National Semiconductor has introduced the PowerWise LMV1088 dual-input microphone array amplifier - the first in a line of audio products using analog far-field noise suppression technology (see/hear online demo). The device is said to reduce background noise and improve voice communication clarity in applications such as mobile phones, two-way radios and powered headsets, while at the same time consuming one-tenth the power of comparable DSP or microprocessor-based software-based systems.
According to the company, the far-field noise suppression 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 sub-band frequency processing algorithms to implement noise suppression.
Unlike DSPs and processors, the LMV1088's continuous-time analog processing provides instantaneous response to voice and background noise signals, and allows integration of noise suppression performance in phone handsets or powered headsets without requiring the development time to write and test voice-processing programming code.
The amplifier draws 1 mA of supply current. Other specifications include a PSRR of 85 dB at 1 KHz, an SNR of 60 dB and less than 1% THD+N.
The LMV1088 is designed for use with two microphones in an end-fire array configuration. The microphones can be spaced in a line 1.5 to 2.5 cm apart from each other, or the equivalent acoustic path distance. The optimal distance for the person speaking into the handset or headset microphone is 2 to 10 cm.
Automatic calibration circuitry compensates for the microphones' gain and frequency response variations, eliminating the need to use matched microphone sets, while allowing flexible placement of the microphones in the final product. The calibration data is stored in internal EEPROM.
The calibration sequence chooses the optimized coefficients for the two microphones' spacing and acoustical environment. The LMV1088 features four I2C-compatible, selectable operating modes: default noise reduction, microphone 1 pass through, microphone 2 pass through or microphone 1 & 2 sum.
The LMV1088 is available in a miniature 3.5- x 3.5-mm, 36-bump micro SMDxt package and priced at $9.95 each in 1,000-unit quantities.
National Semiconductor, 1-800-272-9959, www.national.com
Online demo of LMV1088 noise suppression
LMV1088 information page
LMV1088 datasheet (PDF)