This work focuses on the design of low-power fully-integrated pulse oximeter front-ends and transimpedance amplifiers. Mathematical modelling and numerical simulations are employed to systematically quantify the trade-offs involved in the design of such a front-end and investigate the specific challenges arising from the requirements for low- power and full integration. The response speed, stability, power consumption and noise characteristics of the front-end's transimpedance amplifier are identified as significant points of interest. The performance of several transimpedance amplifier topologies is investigated. Topologies based on switched integration of the input are shown to be advantageous and employed in the design of a mixed-signal pulse oximeter front-end which was fabricated in the AMS 0:35 m technology. Extensive electrical and physiological measurements are reported showing that the proposed front-end can achieve LED power consumptions below 400 W and a total power consumption of less than 1 mW with a mean signal-to-noise ratio exceeding 39 dB at the detector. This performance is among the best ever reported and an order of magnitude better than most commercial pulse oximeters. Ways to lower this power consumption even further are identified. This work also reports on a novel self-biased photoreceptor (transimpedance amplifier) topology. A detailed comparison with previous state-of-the-art designs is carried out that provides new, useful insights on the photoreceptors' performance. The proposed design is concluded to be beneficial for applications where extremely low power and fast settling are of high significance.