Systems and methods are described that relate to a body-mountable device. The body-mountable device includes a first light source and a second light source, which may emit light having at least a first and second wavelength, respectively. The body-mountable device includes at least one sensor configured to detect light having the first wavelength and the second wavelength. The body-mountable device includes a battery, a communication interface, and a controller. The controller includes a memory, a processor, and a sigma-delta analog-to-digital converter (ADC) having one or more channels. The controller performs various operations, such as causing the first light source and the second light sources to emit light and receiving information indicative of at least one physiological parameter via the at least one sensor. The controller may also perform processing, via the sigma delta ADC, the information indicative of the at least one physiological parameter so as to provide physiological data.
