  Measuring the bioelectric signals is one of the key functions in wearable
healthcare devices and implantable medical devices. The use of wearable
healthcare devices has made continuous and immediate monitoring of personal
health status possible. Implantable medical devices have played an important
role throughout the fields of neuroscience, brain-machine (or brain-computer)
interface, and rehabilitation technology. Over the last five decades, the
bioelectric signals have been observed through a variety of biopotential
recording front-ends, along with advances in semiconductor technology scaling
and circuit techniques. Also, for reliable and continuous signal acquisition,
the front-end architectures have evolved while maintaining low power and low
noise performance. In this article, the architecture history of the
biopotential recording front-ends developed since the 1970s is surveyed, and
overall key circuit techniques are discussed. Depending on the bioelectric
signals being measured, appropriate front-end architecture needs to be chosen,
and the characteristics and challenges of each architecture are also covered in
this article.
