"A Modified Delta-Sigxa Quantizer To Obtain High Resolution A/D Conversion With Small Excess Sample Rates"

There are a number of techniques [1] which use a combination of excess sample rate and signal processing to obtain enhanced resolution analog-to-digital conversion (ADC) from a reduced resolution quantizer. The common thread in these techniques is the formation of correlated data by sampling and quantizing a bandlinited signal at a rate considerably above its Nyquist rate. Coherent signal processing of these correlated samples improves the signal to quantizing noise ratio by the processing gain (ie., the ratio of coherent gain to incoherent gain) of the processing. This improvement in signal to noise ratio (SNR) is viewed as the conversion of excess sample rate to additional bits of quantization. Feedback and spectral noise shaping improves the rate at which we can exchange the excess sample ratio for improved resolution. One system which successfully ap- plies both techniques is the delta-sigma modulator. This paper presents a number of modifications to the standard delta-sigma configuration which permits high resolution conversion while operating at small excess sample ratios.