Smartphones audio chip cuts out noise in


The LM49155 is a fully integrated audio subsystem designed for portable handheld applications such as cellular phones. The LM49155 combines a Noise Suppression microphone amplifier, a 1.35W mono class D amplifier with ALC, class AB earpiece driver with AGC, a high efficiency, stereo, ground referenced headphone amplifier with click pop suppression and I 2C modes select and volume control.

The LM49155 features analog fully differential input, and differential output microphone amplifier designed to reduce background acoustic noise, while delivering superb speech clarity in voice communication applications. Downlink SNR enhancement with an advanced acoustic AGC technology to adjust output levels.

Smartphones audio chip cuts out noise in

The LM49155 speaker amplifier features National’s unique output limiter that provides both a no-clip feature and speaker protection. The E 2S class D amplifier features a patented, ultra low EMI PWM architecture that significantly reduces RF emissions while preserving audio quality and efficiency. The headphone drivers feature National’s ground referenced architecture that creates a ground-referenced output from a single, low-voltage supply.

The LM49155 is available in an ultra-small 36-bump micro SMD package (3.434mm x 3.459mm x 0.6mm).

Notice: This document is not a full datasheet. For more information regarding this product or to order samples please contact your local National Semiconductor sales office or visit


  • Noise cancellation for uplink and downlink without DSP-type artifacts, distortions or delays
  • Adapting AGC on ambient noise level & downlink signal strength for earpiece
  • Downlink adjustable noise-reducing high pass filter
  • E 2S Class D Amplifier with ALC
  • Ground Referenced Headphone Outputs with Advanced Click Pop Suppression
  • Micro-power shutdown

National Semiconductor has added a noise reduction circuit to its analogue audio chip for minimising background noise in smartphones.

The LM49155 provides uplink noise suppression and downlink signal-to-noise ratio (SNR).

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.

Power consumption is specified at 3.7mA of quiescent current for the earpiece amplifier and microphone amplifier signal path.

The LM49155’s uplink noise suppression technology rejects far-field noise through a unique 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.

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