Next-Generation RF Front-End Design Methods for Direct \Delta\Sigma Receivers

RF-to-digital conversion is a recent approach to digital-intensive wireless receiver operation. Such converters often employ delta-sigma (ΔΣ) modulation to transcend the traditional divide between receiver RF front-ends and baseband analog-to-digital converters (ADC). Research on the direct delta-sigma receiver (DDSR) architecture is one example of the emergence of next-generation ΔΣ modulators. It embeds a direct conversion receiver front-end as part of a feedback-type ΔΣ modulator structure with an active loop filter, which extends ADC operation to RF and changes the role of the low-noise amplifier (LNA) and mixing stages. RF-to-digital converters thus merge the two formerly separate design domains, requiring a paradigm shift in both RF and ADC design methods. Accordingly, this paper uses the DDSR as an example to bridge the gap between RF and ADC design, by providing a systematic understanding of the role, modeling, and design strategy of the related complete RF front-end. Most importantly, the analysis produces new design equations that link analog RF stage properties to their continuous-time (CT) ΔΣ modulator coefficients, thus providing a useful circuit design tool.