A common analog design challenge is to convert a small, noisy, or perhaps near-rail signal into an accurate digital representation. Any analog design engineer worth their salt would know to employ an analog front end (AFE) to achieve this task. However, what would be the best topology: non-inverting, difference amplifier, or other, to obtain accuracy and precision at minimal complexity and cost?
Before deciding on a topology, it is important to understand the purpose of an AFE and its principles of operation, such as amplification, filtering and setting common-mode voltage. Then a deeper dive can be taken into the advantages and disadvantages of each of the popular AFE topologies to determine the best fit for a specific application. Completing the AFE design with the proper ADC is critical to guarantee the correct digital signal.
This article looks at three basic AFE topologies–the non-inverting amplifier, the difference amplifier, and the instrumentation amplifier–and their key attributes and tradeoffs, along with sources of error and non-linearity. It is presented in two parts, as pdf files (no registration required):
Part 1: Introduction, the non-inverting amplifier, and the difference amplifier, click here.
Part 2: The instrumentation amplifier, IA input/output range, amplifier specifications, tools, and conclusion, click here.
About the Author
Jason Seitz is staff applications engineer for National Semiconductor’s Precision Systems group working on National’s precision, low-power and low-voltage operational amplifiers. Previously, Seitz worked as a product quality engineer in National’s Worldwide Quality Network. Seitz received his bachelor’s of science degree in electrical engineering from the University of California at Davis and his master’s of science degree in electrical engineering at Santa Clara University.