National Semiconductor has introduced the analogue audio subsystem with integrated noise reduction for use in smartphones and full-featured phones. The PowerWise LM49155 improves the talker's voice-signal-to-background-noise ratio while retaining natural speech quality. The subsystem delivers noise reduction at low power consumption, consuming 3.7mA of quiescent current for the earpiece amplifier and microphone amplifier signal path. The subsystem can be used to enable the rapid integration of noise suppression performance in telephone handsets. The LM49155 provides uplink noise suppression and downlink signal-to-noise ratio enhancement in a 36-bump, micro SMD package measuring 3.4×3.4mm. The subsystem includes a high-efficiency, 1.35W Class D speaker driver with automatic level control, ground-referenced headphone amplifier with click-pop suppression, and mixing and volume control. The noise suppression technology is also available in a discrete noise-processing IC, the LMV1099. It delivers 34dB uplink far-field noise suppression at 1kHz, near-field SNR enhancement of 6 to 18dB, and downlink SNR improvement of 16dB. The device provides uplink and downlink total harmonic distortion plus noise (THD+N) of 0.1%, shutdown current at 0.07µA, and supply current of 3.7mA. The IC operates from a supply voltage range of 2.7 to 5.5V, and is supplied in a 25-bump micro SMD package.
