A self-calibrated 2–1–1 cascaded continuous-time ΔΣ modulator

A 2-1-1 cascaded continuous-time DeltaSigma modulator (DSM) is self-calibrated with LMS-based adaptation. Its noise cancellation filter (NCF) is derived using a parameter-based continuous-time (CT) to discrete-time (DT) transform. These techniques reduce the quantization noise leakage due to the mismatch between analog modulator and digital NCF. A 0.18-mum CMOS prototype operating at 360 MHz with a 1-V
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full-scale demonstrates a leakage noise spectral density below 10 nV/radicHz over a 30-MHz bandwidth after the capacitors in the Gm-C loop filters are self-trimmed with a 1.1% step. This level of noise leakage is well below the noise floor of most CT DSM designs.