《WM8974资料》由会员分享，可在线阅读，更多相关《WM8974资料（87页珍藏版）》请在金锄头文库上搜索。
1、w WM8974Mono CODEC with Speaker Driver WOLFSON MICROELECTRONICS plc To receive regular email updates, sign up at http:/ Production Data, Rev 4.5, September 2008 Copyright 2008 Wolfson Microelectronics plc DESCRIPTION The WM8974 is a low power, high quality mono CODEC designed for portable applicatio
2、ns such as Digital Still Camera or Digital Voice Recorder. The device integrates support for a differential or single ended mic, and includes drivers for speakers or headphone, and mono line output. External component requirements are reduced as no separate microphone or headphone amplifiers are req
3、uired. Advanced Sigma Delta Converters are used along with digital decimation and interpolation filters to give high quality audio at sample rates from 8 to 48ks/s. Additional digital filtering options are available in the ADC path, to cater for application filtering such as wind noise reduction, pl
4、us an advanced mixed signal ALC function with noise gate is provided. The digital audio interface supports A-law and -law companding. An on-chip PLL is provided to generate the required Master Clock from an external reference clock. The PLL clock can also be output if required elsewhere in the syste
5、m. The WM8974 operates at supply voltages from 2.5 to 3.6V, although the digital supplies can operate at voltages down to 1.71V to save power. The speaker and mono outputs use a separate supply of up to 5V which enables increased output power if required. Different sections of the chip can also be p
6、owered down under software control by way of the selectable two or three wire control interface. WM8974 is supplied in a very small 4x4mm QFN package, offering high levels of functionality in minimum board area, with high thermal performance. FEATURES Mono CODEC: Audio sample rates:8, 11.025, 16, 22
7、.05, 24, 32, 44.1, 48kHz DAC SNR 98dB, THD -84dB (A-weighted 8 48ks/s) ADC SNR 94dB, THD -83dB (A-weighted 8 48ks/s) On-chip Headphone/Speaker Driver with cap-less connect - 40mW output power into 16 / 3.3V SPKVDD - BTL speaker drive 0.9W into 8 / 5V SPKVDD Additional MONO Line output Multiple analo
8、g or Aux inputs, plus analog bypass path Mic Preamps: Differential or single end Microphone Interface - Programmable preamp gain - Psuedo differential inputs with common mode rejection - Programmable ALC / Noise Gate in ADC path Low-noise bias supplied for electret microphones OTHER FEATURES 5 band
9、EQ (record or playback path) Digital Playback Limiter Programmable ADC High Pass Filter (wind noise reduction) Programmable ADC Notch Filter On-chip PLL Low power, low voltage - 2.5V to 3.6V (digital: 1.71V to 3.6V) - power consumption limit only) signals below this threshold are unaffected by the l
10、imiter. Signals above the upper threshold are attenuated at a specific attack rate (set by the LIMATK register bits) until the signal falls below the threshold. The limiter also has a lower threshold 1dB below the upper threshold. When the signal falls below the lower threshold the signal is amplifi
11、ed at a specific decay rate (controlled by LIMDCY register bits) until a gain of 0dB is reached. Both threshold levels are controlled by the LIMLVL register bits. The upper threshold is 0.5dB above the value programmed by LIMLVL and the lower threshold is 0.5dB below the LIMLVL value. WM8974 Product
12、ion Data w PD, Rev 4.5, September 2008 38 VOLUME BOOST The limiter has programmable upper gain which boosts signals below the threshold to compress the dynamic range of the signal and increase its perceived loudness. This operates as an ALC function with limited boost capability. The volume boost is
13、 from 0dB to +12dB in 1dB steps, controlled by the LIMBOOST register bits. The output limiter volume boost can also be used as a stand alone digital gain boost when the limiter is disabled. Production Data WM8974 w PD, Rev 4.5, September 2008 39 REGISTER ADDRESS BIT LABEL DEFAULT DESCRIPTION 3:0 LIM
14、ATK 0010 Limiter Attack time (per 6dB gain change) for 44.1kHz sampling. Note that these will scale with sample rate. 0000=94us 0001=188s 0010=375us 0011=750us 0100=1.5ms 0101=3ms 0110=6ms 0111=12ms 1000=24ms 1001=48ms 1010=96ms 1011 to 1111=192ms 7:4 LIMDCY 0011 Limiter Decay time (per 6dB gain cha
15、nge) for 44.1kHz sampling. Note that these will scale with sample rate: 0000=750us 0001=1.5ms 0010=3ms 0011=6ms 0100=12ms 0101=24ms 0110=48ms 0111=96ms 1000=192ms 1001=384ms 1010=768ms 1011 to 1111=1.536s R24 DAC digital limiter control 1 8 LIMEN 0 Enable the DAC digital limiter: 0=disabled 1=enable
16、d 3:0 LIMBOOST 0000 Limiter volume boost (can be used as a stand alone volume boost when LIMEN=0): 0000=0dB 0001=+1dB 0010=+2dB (1dB steps) 1011=+11dB 1100=+12dB 1101 to 1111=reserved R25 DAC digital limiter control 2 6:4 LIMLVL 000 Programmable signal threshold level (determines level at which the limit
