There are many kinds of commercial memory cards on the market. Due to great improvements in modern technology, they have great amounts of capacity, low power consumption, and are easily available. Therefore a data logging system using a commercial memory card is a convenient and economic procedure. This thesis introduces a wearable data logging system for physiological recording. A front-end amplifier, analog to digital converter, and a memory card controller compose the basis of this system. The front-end amplifier uses a switched-capacitor structure, so the output waveform is discrete in regard to the time domain. This brings an advantage in saving power for not keeping charging the load capacitance. Lateral bipolar transistors fabricated in a CMOS process are used as input devices. A conventional ADC is used to convert the amplified signal into digital data. Finally MultiMediaCard is chosen as a large storage space. This thesis contributes the analysis, design and measurement of the amplifier front-end. In addition, the design and implementation of a controller circuit for sequential data storage into the MultiMediaCard memory is described. Special attention was paid to achieving a small area, low-complexity and low-power implementation suitable for integration. Measured results obtained from a preliminary FPGA implementation are reported and the functionality of a complete logger circuit is demonstrated with measured results.