Biomedical electronics has gained significant attention in healthcare industry, where biomedical devices are becoming widespread for use in the diagnosis of disease or other conditions, or in the cure, mitigation and prevention of disease. They are used in wide variety of conditions such as cardiac pacemakers for cardiac arrhythmia, cochlear implants for deafness or retinal implants for blindness? large amount of activity is being researched in brain-machine interfaces for paralysis, stroke, and blindness. A general biomedical device comprises energy source, analog preprocessing, analog-to digital conversion (ADC), digital signal preprocessing, and communication subsystem, each of which must be designed for minimum energy consumption to adhere to the stringent energy constraint. The ADC is one of the key building blocks in all biomedical electronic systems. As of particular interest in this thesis, the ADC is an important block in the sensing stage of the biomedical systems, such as implantable devices, for accurate detection of the physiological signals like electrocardiogram (ECG) and electroencephalogram (EEG).