Quantifying Biomedical Amplifier Efficiency: The noise efficiency factor

There has been a long-standing interest in controlling and instrumenting the human body. Whether to restore lost function with neural prosthetics, monitor blood glucose levels, or augment human capabilities, there are countless opportunities for sensors inside (
e.g.,
ingestible, injectable, and implantable) and outside (
e.g.,
wearable) the body. However, many challenges exist when instrumenting the body. First, many use cases (
e.g.,
implanted sensors) require long-term recording to capture anomalous behavior—sometimes with limited accessibility—necessitating ultralow power consumption. Second, the power reduction challenge is further exacerbated by size constraints, which limit battery capacity or harvestable energy levels. Third, the signals of interest are often low bandwidth (kHz) and small in amplitude (µV to mV); thus, low-noise front ends are needed. Addressing these challenges has led to a large body of work on the design of highly power-efficient, low-noise amplifiers for biomedical integrated circuits.