Wolfson 公司的WM8918是用于手提音頻設備的高性能超低功耗立體聲DAC，DAC到耳機播放的靜態功耗3.8mW，DAC的SNR為96dB，THD為-86dB，標準取樣速率從8kHz到96kHz，集成的PLL提供了所有必須的時鐘，主要用在PMP，無線手機和游戲機等。本文介紹了WM8918主要特性，音頻信號通路框圖，推薦的外接元件圖以及WM8918-6201-FL32-M-REV1用戶Mini板配置圖，多種應用的信號通路圖，電路圖和材料清單，PCB布局圖。
The WM8918 is a high performance ultra-low power stereo DAC optimised for portable audio applications.
The device features stereo ground-referenced headphone amplifiers using the Wolfson ‘Class-W’ amplifier techniques - incorporating an innovative dual-mode charge pump architecture - to optimise efficiency and power consumption during playback. The ground-referenced headphone and line outputs eliminate AC coupling capacitors, and both outputs include common mode feedback paths to reject ground noise.
Control sequences for audio path setup can be pre-loaded and executed by an integrated control write sequencer to reduce software driver development and minimise pops and clicks via Wolfson’s SilentSwitch™ technology.
The analogue input stage can be configured for single ended or differential inputs. Up to 3 stereo microphone or line inputs may be connected. The input impedance is constant with PGA gain setting.
A stereo digital microphone interface is provided, with a choice of two inputs. The analogue or digital microphone inputs can be mixed into the headphone or line output paths.
A dynamic range controller provides compression and level control to support a wide range of portable recording applications in conjunction with the digital microphone interface. Anti-clip and quick release features offer good performance in the presence of loud impulsive noises.
ReTuneTM Mobile 5-band parametric equaliser with fully programmable coefficients is integrated for optimization of speaker characteristics. Programmable dynamic range control is also available for maximizing loudness, protecting speakers from clipping and preventing premature shutdown due to battery droop.
Common audio sampling frequencies are supported from a wide range of external clocks, either directly or generated via the FLL.
The WM8918 can operate directly from a single 1.8V switched supply. For optimal power consumption, the digitalcore can be operated from a 1.0V supply.
WM8918主要特性：
3.8mW quiescent power consumption for DAC to headphone playback
DAC SNR 96dB typical, THD -86dB typical
2.4mW quiescent power consumption for analogue bypass playback
Control write sequencer for pop minimised start-up and shutdown
Single register write for default start-up sequence
Integrated FLL provides all necessary clocks
- Self-clocking modes allow processor to sleep
- All standard sample rates from 8kHz to 96kHz
Stereo digital microphone input
3 single ended inputs per stereo channel
1 fully differential mic / line input per stereo channel
Digital Dynamic Range Controller (compressor / limiter)
Digital sidetone mixing
Ground-referenced headphone driver
Ground-referenced line outputs
32-pin QFN package (4x4mm, 0.4mm pitch)
WM8918應用：
Wireless headsets
Portable multimedia players
Handheld gaming
圖1。WM8918方框圖
圖2。WM8918音頻信號通路框圖
圖3。WM8918推薦的外接元件圖
WM8918-6201-FL32-M-REV1用戶Mini板
The WM8918-6201-FL32-M-REV1 Customer Mini Board is compatible with the 6201-EV1-REV3 customer evaluation board and together provide a complete hardware platform for evaluation of the WM8918. The WM8918 Customer Mini Board can also be used independently and connected directly to a processor board using flying wires or appropriate headers. This document will cover both, but performance data will be based on the Wolfson system with 6201-EV1-REV3 main board.
Configurations covered are listed below:
Electrical S/PDIF DAC to headphone playback
Optical S/PDIF DAC to lineout playback
Line-in bypass to headphone output
USB streaming DAC to headphone playback
圖4。WM8918-6201-FL32-M-REV1板配置圖
圖5。DAC到耳機播放的信號通路圖
圖6。DAC到線輸出的信號通路圖
圖7。線路輸入到耳機播放的信號通路圖
圖8。WM8918-6201-FL32-M-REV1板電路圖：WM8918
圖9。WM8918-6201-FL32-M-REV1板電路圖：MIC輸入和耳機輸出
圖9。WM8918-6201-FL32-M-REV1板電路圖：Mini板插座
圖10。WM8918-6201-FL32-M-REV1板電路圖：連接表格
圖11。WM8918-6201-FL32-M-REV1板PCB頂層布局圖
WM8918-6201-FL32-M-REV1板材料清單（BOM）：
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