Low power subsystem maintains natural voice quality in noisy environments
1 min read
National Semiconductor has launched what it claims to be the industry's first analogue audio subsystem with integrated noise reduction for use in smartphones and full featured phones.
The PowerWise LM49155 is designed to improve the talker's voice-signal-to-background-noise ratio while retaining natural speech quality. According to National, phone users can now experience clearer voice calls in noisy environments on both transmit and receive ends of the communications link.
The LM49155 is also said to enable increased accuracy of voice recognition systems by minimising background noise.
The audio subsystem consumes 3.7mA of quiescent current for the earpiece amplifier and microphone amplifier signal path. National Semiconductor claims it 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.
The LM49155 provides uplink noise suppression and downlink signal-to-noise ratio (snr) enhancement in a 36 bump micro smd package measuring 3.4x3.4mm. The subsystem includes a 1.35W Class D speaker driver with automatic level control, ground-referenced headphone amplifier with click-pop suppression, and mixing and volume control.
The uplink noise suppression technology rejects far-field noise through a two-microphone amplifier implementation. Downlink voice intelligibility is improved by enhancing the snr between the handset's earpiece signal level and the ambient noise level.
The LM49155 preserves uplink near-field voice signals within close range, while rejecting acoustic noise more than 0.5metres away from the microphones. In addition, it provides continuous downlink signal adjustments so the caller's voice is always clearly heard regardless of the listener's environment.
