模数转换基础.ppt

Number of data (Rule of thumb) Overload on purpose. The input signal must sweep more than the input range to generate all codes. Tips for Histogram Method for ramp wave histogram for sine wave histogram (One code occurs at least 10 times.) ADC Dynamic Performance Specifications Total harmonic distortion (THD) Signal-to-noise plus distortion (SND) Effective Number of Bits (Neff) Signal-to-noise ratio (SNR) Spurious free dynamic range (SFDR) Components of Distortion Measurement Fundamental Harmonic Noise Spur Bin Number Total Harmonic Distortion, THD The total harmonic distortion (THD) is the ratio of the rms sum of the first N harmonic components (typically up to the 5th harmonic) to the rms value of a full-scale input signal. THD is expressed in dB. Hf H4 H2 H3 H5 Signal-to-Noise Ratio, SNR Signal to Noise Ratio (SNR) is the ratio of the rms value of the input signal to the rms sum of all other spectral components below Nyquist frequency, excluding harmonics and DC. Hf H4 H2 H3 H5 Signal-to-Noise plus Distortion, SND (SINAD) Signal to Noise Distortion is the ratio of the rms value of the input signal to the rms sum of all other spectral components below Nyquist frequency, including everything but DC. Hf H4 H2 H3 H5 Spurious Free Dynamic Range, SFDR Spurious free dynamic range (SFDR) is the ratio of the largest spectral component excluding DC to the rms value of the full-scale input signal. Vmsc Vf Quantization Error of an ADC Effective Number of Bits, Neff, ENOB The theoretical resolution of an ADC is reduced by Quantization noise DNL INL Missing Codes Noise The quantization noise is expressed by the effective number of bits. For a linear ADC, it is calculated as: Neff = SNR – 1.76 6.02 This means that the maximum resolution of the tested ADC is that of an ideal ADC with Neff bits. Theoretical/Measured SNR B= Number of Bits L = Number of Levels = 2B q = Quantization Step Size AC Average Power = Quick Reference Test Example 1 There are 8 bi