Switched current sigma-delta A/D converter for a CMOS subscriber line analog front end

This paper describes the design and testing of a 1-bit A/D converter based on the sigma-delta modulation principle. Unlike the conventional realisations using the switched capacitor approach, the current switching technique uses the current level as a variable. In order to check the feasibility and advantages of this technique, a first order 1-bit A/D converter and a second order 1-bit A/D converter were designed. In the first order 1-bit A/D converter a time-continuous current-integrator is used as filter. The circuit has been designed realised and tested. In the second order 1-bit A/D converter the filter is based on the analog sampling and processing of a current signal. The second order filter is implemented with class AB switched current memory cells. The design has been simulated and processed in ES2 1.5 μm CMOS technology