The MOSbius Field-Programmable Transistor Array Is Like an FPGA for Analog Circuit Design

A team at Columbia University's department of electrical engineering is looking to make it easier for students to experiment with analog electronics in hardware — by developing the transistor-level equivalent of a field-programmable gate array (FPGA), dubbed MOSbius.

"The MOSbius chip contains nMOS and pMOS [N-type and P-type metal-oxide semiconductor] devices as individual transistors," the team behind the project explains, "as well as in typical configurations like current mirrors, differential pairs, common source configuration, simple operational transconductance amplifiers or inverters. [The] transistors and circuits on the MOSbius chip allow the student to create an electronic circuit that they can evaluate experimentally."

"As these [transistors] are the building blocks of most analog integrated circuits today," project lead Peter Kinget explains in a piece for IEEE Spectrum, "designing with the MOSbius provides experience that's directly relevant to creating real chips. We program the MOSbius's matrix using a Raspberry Pi Pico running a Python script that turns a simple JSON text file into the desired bitstream. If you want, though, you can use pretty much any 3.3-volt microcontroller that supports Python."

In effect, the MOSbius is a field-programmable transistor array (FPTA) — inspired by, but different to, a field-programmable gate array (FPGA). By being able to control the chip at the level of individual transistors, it's possible to use the MOSbius as a device in a range of analog circuits. "The origin of the MOSbius was serendipitous," Kinget notes. "While preparing a set of students’ IC projects to be fabricated, we realized we had room to squeeze one more chip into the batch if we could meet the shipping deadline. Six weeks later, the MOSbius was off to production!"

More information on the MOSbius is available on the project website; Kinget is making a small number of excess units available at a "nominal price" of $150, and is working on a revised design that may be produced in larger quantities if a commercial partner for the project can be found.