2.3. Operational Transconductance Amplifier Experiments#
With the MOSbius chip you can build an OTA from scratch and then measure its DC, AC, transient, noise … performance including probing the waveforms at internal nodes. You have to choose a topology, select transistor sizes, and bias currents. You further have to insert a frequency compensation network and feedback network.
Many topologies can be built including:
single-stage OTAs,
two-stage Miller-compensated OTAs,
folded-cascode OTAs,
and even a fully differential two-stage Miller-compensated OTA.
The chip has enough transistors to build four single-ended OTAs making possible experiments of small analog systems.
The student can do hand calculations to size the OTA, run simulations to verify biasing, small-signal parameters and performance, and then compare measured results to calculations and simulations.
Last but not least, the experiments require careful thinking about how to conduct the circuit-parameter characterization and how to deal with non-idealities like loading, parasitics or offsets (which are often overlooked in simulations).