Design and Implementation of a Low-Power SAR-ADC with Flexible Sample-Rate and Internal Calibration

Abstract: The objective of this Master's thesis was to design and implement a low power Analog to Digital Converter (ADC) used for sensor measurements. In the complete measurement unit, in which the ADC is part of, different sensors will be measured. One set of these sensors are three strain gauges with weak output signals which are to be pre-amplified before being converted. The focus of the application for the ADC has been these sensors as they were considered a limiting factor. The report describes theory for the algorithmic and incremental converter as well as a hybrid converter utilizing both of the two converter structures. All converters are based on one operational amplifier and they operate in repetitive fashions to obtain power efficient designs on a small chip area although at low conversion rates. Two converters have been designed and implemented to different degrees of completeness. One is a 13 bit algorithmic (or cyclic) converter which uses a switching scheme to reduce the problem of capacitor mismatch. This converter was implemented at transistor level and evaluated separately and to some extent also with sub-components. The second converter is a hybrid converter using both the operation of the algorithmic and incremental converter to obtain 16 bits of resolution while still having a fairly high sample rate.