The PowerWise LM49155 from National Semiconductor is the industry’s first analog audio subsystem with integrated noise reduction for use in smart phones and full-featured phones, according to the company. It dramatically improves the user’s voice-signal-to-background-noise ratio while retaining natural speech quality, National says, noting that users can enjoy clearer voice calls in noisy environments on the transmit and receive ends of the communications link. The LM49155 also enables the increased accuracy of voice recognition systems by minimizing background noise. 

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The LM49155 is designed to deliver noise reduction at the lowest power consumption, consuming 3.7 mA of quiescent current for the earpiece amplifier and microphone amplifier signal path. The subsystem’s ease of use enables the rapid integration of noise suppression performance in phone handsets, without the added development time required to write and test voice-processing programming code for a DSP or microprocessor, National says.

Furthermore, the LM49115 provides uplink noise suppression and downlink signal-to-noise ratio (SNR) enhancement in a 36-bump micro-SMD (surface-mount device) package measuring 3.4 by 3.4 mm. It includes a high-efficiency, 1.35-W class D speaker driver with automatic level control (ALC), a ground-referenced headphone amplifier with click-pop suppression, and mixing and volume control.

The uplink noise suppression technology rejects far-field noise through a unique two-microphone amplifier implementation. Enhancing the SNR between the handset’s earpiece signal level and the ambient noise level improves the downlink voice intelligibility. The LM49155 also preserves uplink near-field voice signals within close range while rejecting acoustic noise more than 0.5 m away from the microphones. And, the subsystem provides continuous downlink signal adjustments so the caller’s voice is always clearly heard regardless of the listener’s environment.

This noise suppression technology is available in the company’s LMV1099 discrete noise-processing IC as well. It delivers 34-dB uplink far-field noise suppression at 1 kHz, near-field SNR enhancement of 6 to 18 dB, and downlink SNR improvement of 16 dB. Also, it provides uplink and downlink total harmonic distortion plus noise (THD+N) of 0.1%, shutdown current at 0.07 µA and supply current of 3.7 mA. It operates from a supply voltage range of 2.7 to 5.5 V and comes in a 25-bump micro-SMD package.

Available now, the LM49155 costs $2.25 and the LMV1099 costs $1.50, both in 1000-unit quantities.

National Semiconductor

www.national.com/pf/LM/LM49155.html

www.national.com/pf/LM/LMV1099.html