NS 公司的LM49155 是高度集成的PowerWise音頻子系統，集成了噪音抑制麥克風放大器，1.35W單聲道帶ALC的D類放大器，帶AGC的AB類耳機驅動器，帶開關機聲抑制的高效立體聲參考地耳機放大器以及I2C模式選擇和音量控制。主要用于手機和手提電子設備。本文介紹了LM49155主要指標，簡化方框圖以及典型應用電路。
Uplink Noise Suppression & Downlink SNR Enhancement Analog Audio Subsystem
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 I2C 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.
The LM49155 speaker amplifier features National’s unique output limiter that provides both a no-clip feature and speaker protection. The E2S 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).
LM49155主要指標：
■ Uplink Far Field Noise Suppression Electrical FFNSE at f = 1kHz 34dB (typ)
■ Downlink SNR Enhancement Earpiece Amplifier
Near-Field SNR Enhancement 6 to 18dB (typ)
Downlink SNRIE 16dB (typ)
■ Class D Loudspeaker Amplifier RL = 15μH+8Ω+15μH
POUT, THD+N ≤ %, VDD = 5.0V 1.35W (typ)
■ Headphone Amplifier RL = 32Ω
POUT, THD+N ≤ %, HPVDD = 1.8V 19mW (typ)
LM49155主要特性：
■ Noise cancellation for uplink and downlink without DSPtype artifacts, distortions or delays
■ Adapting AGC on ambient noise level & downlink signal strength for earpiece
■ Downlink adjustable noise-reducing high pass filter
■ E2S Class D Amplifier with ALC
■ Ground Referenced Headphone Outputs with Advanced Click Pop Suppression
■ Micro-power shutdown
LM49155應用：
■ Mobile Phones
■ Portable Electronic Devices
圖1。LM49155簡化方框圖
圖2。LM49155典型應用框圖
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