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WM8731SEDS/R 数据表(PDF) 43 Page - Wolfson Microelectronics plc |
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WM8731SEDS/R 数据表(HTML) 43 Page - Wolfson Microelectronics plc |
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43 / 63 page ![]() WM8731 / WM8731L Production Data w PD Rev 4.3 August 2006 43 USB MODE SAMPLE RATES In USB mode the MCLK/crystal oscillator input is 12MHz only. SAMPLING RATE ADC DAC MCLK FREQUENCY SAMPLE RATE REGISTER SETTINGS DIGITAL FILTER TYPE kHz kHz MHz BOSR SR3 SR2 SR1 SR0 48 48 12.000 0 0 0 0 0 0 44.1 (Note 2) 44.1 (Note 2) 12.000 1 1 0 0 0 1 48 8 12.000 0 0 0 0 1 0 44.1 (Note 2) 8 (Note 1) 12.000 1 1 0 0 1 1 8 48 12.000 0 0 0 1 0 0 8 ((Note 1) 44.1 (Note 2) 12.000 1 1 0 1 0 1 8 8 12.000 0 0 0 1 1 0 8 (Note 1) 8 (Note 1) 12.000 1 1 0 1 1 1 32 32 12.000 0 0 1 1 0 0 96 96 12.000 0 0 1 1 1 3 88.2 (Note 3) 88.2 (Note 3) 12.000 1 1 1 1 1 2 Table 21 USB Mode Sample Rate Look-up Table Notes: 1. 8k not exact, actual = 8.021kHz 2. 44.1k not exact, actual = 44.118kHz 3. 88.1k not exact, actual = 88.235kHz 4. All other combinations of BOSR and SR[3:0] that are not in the truth table are invalid The table above can be used to set up the device to work with various sample rate combinations. For example if the user wishes to use the WM8731/L in USB mode with the ADC and DAC sample rates at 48kHz and 48kHz respectively then the device should be programmed with BOSR = 0, SR3 = 0, SR2 = 0, SR1 = 0 and SR0 = 0. The ADC and DAC will then operate with a Digital Filter of type 0, refer to Digital Filter Characteristics section for an explanation of the different filter types. The BOSR bit represents the base over-sampling rate. This is the rate that the WM8731/L digital signal processing is carried out at and the sampling rate will always be a sub-multiple of this. In USB mode, with BOSR = 0, the base over-sampling rate is defined at 250fs, with BOSR = 1, the base over-sampling rate is defined at 272fs. This can be used to determine the actual audio sampling rate produced by the ADC and required by the DAC. Example scenarios are, :- 1. with a requirement that the ADC data sampling rate is 8kHz and DAC data sampling rate is 48kHz the device is programmed with BOSR = 0 (250fs), SR3 = 0, SR2 = 0, SR1 = 1, SR0 = 0.The ADC will then be exactly 8kHz ( derived from 12MHz/250 x 1/6 ) and the DAC expects data at exactly 48kHz ( derived from 12MHz/250 ). 2. with a requirement that ADC data rate is 8kHz and DAC data rate is 44.1kHz the device is programmed with BOSR = 0 (272fs), SR3 = 0, SR2 = 0, SR1 = 1, SR0 = 0. The ADC will not output data at exactly 8kHz, instead it will be 8.021kHz ( derived from 12MHz/272 x 2/11 ) and the DAC at 44.118kHz ( derived from 12MHz/272 ). A slight (sub 0.5%) pitch shift will therefore results in the 8kHz and 44.1kHz audio data and (more importantly) the user must ensure that |
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