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CS5126 数据表(PDF) 11 Page - Cirrus Logic |
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CS5126 数据表(HTML) 11 Page - Cirrus Logic |
11 / 32 page larly, the acquisition time for the external sam- ple/hold amplifiers must not exceed the mini- mum conversion time of 192 master clock cycles (7.8 µs for 48kHz stereo sampling). Oversampling The CS5126 can alternatively be used to over- sample one channel (monaural) by 2X simply by tying the L/R input high or low. This moves much of the anti-alias burden from analog filters to digital post-filtering. The analog filters’ cor- ner can be pushed out in frequency with lower roll-off, allowing lower passband ripple and more linear phase in the audioband. Digital FIR filtering, meanwhile, can be used to implement high roll-off filters with ultra-low passband rip- ple and perfectly linear phase. Oversampling not only improves system-level filtering performance, but it also enhances the ADC’s dynamic range and distortion charac- teristics. All noise energy in a sampled, digital signal aliases into the baseband between dc and one-half the sampling rate. For an ideal succes- sive-approximation ADC the noise spectral con- tent is white. Therefore, in a 2X oversampling scheme such as 96kHz sampling the ADC’s noise will be be spread uniformly from dc to 48kHz. Digital post-filtering then rejects noise outside of the 20kHz or 22kHz bandwidth, re- sulting in improved signal-to-noise and dynamic range. For a white noise spectrum, a 2X reduc- tion in bandwidth yields a 3dB improvement in dynamic range. Due to its on-chip self-calibration scheme, the CS5126’s dynamic range is limited only by white broadband noise rather than signal-depend- ent DNL errors. Therefore, the CS5126 picks up a full 3dB improvement in dynamic range to 95dB when implemented in 2X oversampling schemes. Oversampling and digital filtering also enhance the ADC’s distortion performance. Consider for example a full-scale 15kHz input signal to the CS5126 sampling at 96kHz. Sampling distortion produces THD of approximately 0.005% (86dB) at the converter’s output. Most of the distortion energy resides in the second and third harmonics VA- VD- AINL* AINR VREF AGND REFBUF +5V* SCLK CLKIN SDATA DGND HOLD +5V -5V Voltage Reference 0.1 µF 0.1 µF f /256 clk f /16 clk fclk 10 Ω Anti Alias Filter Analog Input + 1 µF + 1 µF + 1 µF + 1 µF 1nF 10 Ω 200 Ω CS5126 * AINR can alternatively be used with L/R grounded SLEEP VD+ VA+ L/R 0.1 µF 0.1 µF 0.1 µF Figure 9. Monaural 2X Oversampling Connections CS5126 DS32F1 11 |
类似零件编号 - CS5126 |
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类似说明 - CS5126 |
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