Wolfson 公司的WM8918是用于手提音频设备的高性能超低功耗立体声DAC，DAC到耳机播放的静态功耗3.8mW，DAC的SNR为96dB，THD为-86dB，标准取样速率从8kHz到96kHz，集成的PLL提供了所有必须的时钟，主要用在PMP，无线手机和游戏机等。本文介绍了WM8918主要特性，音频信号通路框图，推荐的外接元件图以及WM8918-6201-FL32-M-REV1用户Mini板配置图，多种应用的信号通路图，电路图和材料清单，PCB布局图。
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应用：
Wireless headsets
Portable multimedia players
Handheld gaming

图1。WM8918方框图

图2。WM8918音频信号通路框图

图3。WM8918推荐的外接元件图

WM8918-6201-FL32-M-REV1用户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

图4。WM8918-6201-FL32-M-REV1板配置图

图5。DAC到耳机播放的信号通路图

图6。DAC到线输出的信号通路图

图7。线路输入到耳机播放的信号通路图


图8。WM8918-6201-FL32-M-REV1板电路图：WM8918

图9。WM8918-6201-FL32-M-REV1板电路图：MIC输入和耳机输出

图9。WM8918-6201-FL32-M-REV1板电路图：Mini板插座

图10。WM8918-6201-FL32-M-REV1板电路图：连接表格

图11。WM8918-6201-FL32-M-REV1板PCB顶层布局图
WM8918-6201-FL32-M-REV1板材料清单（BOM）：