IMPROVED NULL CANCELLATION IN A 6^th-ORDER Σ-Δ MODULATOR REALIZED WITH TWO 3^rd-ORDER SECTIONS

Alan J. Davies, Godi Fischer, Hans-Helge Albrecht, Jürgen Hess

Abstract

This paper presents an improved rnethod to digitally correct for statit, analog circuit imnperfections in a two-stage, 6^th order, cascaded (6-3) sigma-delta modulator. By adding a digital correction term to the output of die digital noise cancellation filter, the first stage parasitic quantization noise due to finite amplifier gain and C-Ratio mismatches can be completely removed. A 6-3 modulator implemented as a fully differential switched-capacitor circuit, designed for an OSR of 16, has heen fabricated in a 1.2 µm double-poly n-well CMOS process. Improvements have been made in the null cancellation leading to approximately a 10 dB increase in SNDR ovor a range of signal amplitudes from 12 µVolts to 500 mV. A peak SNDR/SFDR of 87/100 dB for a 1 MHz sample rate and 84/93 dB for a 2.5 MHz sample rate have heen achieved.

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IMEKO TC

TC4 - Measurement of Electrical Quantities

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