Novel switched-capacitor circuits for delta-sigma modulators

Graduation date: 1997Oversampled delta-sigma modulation is one of the widely used A/D conversion\ud techniques for narrow bandwidth signals. In this study several new lowpass and\ud bandpass delta-sigma modulator architectures as well as novel pseudo-N-path integrators\ud that can be used in implementing these architectures are proposed.\ud By using multiplexing techniques the new lowpass delta-sigma modulator\ud architectures exchange higher clock rates with hardware complexity. For a given\ud oversampling ratio (OSR), the multiplexed first-order delta-sigma modulator achieves a\ud higher resolution. Guaranteed stability is a very desirable feature of these structures.\ud The multi-loop delta-sigma modulator architecture similarly reduces the number of\ud integrators needed to achieve high-resolution conversion for a given OSR. To ensure\ud stability a quantizer with (N+1) bits must be used, where N is the number of loops, or in\ud other words, the order of the delta-sigma modulator. Digital correction or randomizing\ud techniques can be used to eliminate the performance reduction due to digital-to-analog-\ud (D/A) converter nonlinearity error [59], [64].\ud Bandpass delta-sigma modulators are useful for applications such as AM radio\ud receivers, spectrum analyzers, and digital wireless systems. Using z --> -z[superscript N] or z --> z[superscript N] mapping, a low pass delta-sigma modulator can be transformed to a bandpass one. One\ud of the methods to implement the loop filters in bandpass delta-sigma modulators is to use Pseudo-N-Path (PNP) switched-capacitor (SC) integrators. The advantage is that the center frequency occurs exactly at an integer division of the sampling frequency because of the number of physical paths. To achieve maximum resolution, integrators that do not suffer from clock feedthrough peaks are needed. The proposed differential and single-ended novel PNP integrators address this problem [76]. To keep the opamp specifications less stringent while achieving high resolution, these PNP integrators have been further improved with gain compensation techniques [53]