14 bit ΣΔ A Modulator with Multi Bit Feedback

This paper presents a first order ΣΔ Analog to Digital Converter for current measurement in motor controls. The converter consists of a time continuous differential integrator at the input with external capacitors and a four bit pulsewidth modulator in the feedback branch. Highly symmetrically switching inverters are used to couple the differential feedback signal back to the input of the converter. The circuit is implemented in a 1.2 μm CMOS N-Well Process and requires 2 mm
²
for the analog and digital parts of the modulator. Power consumption is about 20 mW. Measurements show the feasibility of this structure for a resolution of 14 bit.