This interview introduces Professor Peter Kingette from Columbia University and his innovative project, Mosbius, a programmable transistor array chip designed to facilitate hands-on integrated circuit (IC) design experiments. The platform, comprising the custom chip, breadboard, and a USB instrument, aims to make complex IC design concepts accessible and measurable for students and professionals. Kingette emphasizes the critical role of measurements in the IC design cycle, arguing that practical lab experience bridges the gap between theory, simulation, and real-world silicon behavior, a skill often lacking in new graduates.
The discussion covers the Mosbius chip's architecture, featuring various N and P transistors with different drive strengths, internal configurable buses (up to 10 nodes), and external pin access. Demonstrations include a "blinking LED" relaxation oscillator and a more advanced delta-sigma analog-to-digital converter, showcasing how users can configure circuits, analyze waveforms, and compare real measurements to LTSpice simulations. The chip, fabricated in a 65nm IO device process, is designed for robustness and has withstood accidental over-voltage applications in university labs. While GDS files are proprietary, a custom SPICE library and detailed lab manuals are openly available, with plans for broader distribution of kits to universities worldwide. Future aspirations include design contests and potential mixed-signal integrations with FPGAs.
Summarizing the Mosbius Project
0:02 Introduction to Mosbius: Peter Kingette, a professor at Columbia University, introduces Mosbius, a programmable transistor array chip designed for hands-on, accessible integrated circuit (IC) design experiments. The name "Mosbius" combines MOSFET and the Mobius loop.
0:46 Professor Kingette's Background & Teaching Philosophy: Kingette emphasizes practical, project-based teaching, including designing and testing student-taped-out chips. He believes in making measurement an integral part of the learning experience, connecting theory, simulation, and real-world silicon.
4:38 Importance of Measurements: Measurements are crucial because silicon behaves physically, often differently from simulations. Practical experience helps designers understand real-world challenges like loading and parasitics, which are often overlooked in simulation-only environments.
8:46 Importance of Documentation: Testing chips designed by others, or even one's own, highlights the critical need for thorough design documentation and datasheets.
9:55 Mosbius Setup & Blinking LED Demo: The core setup includes a Mosbius chip on an adapter PCB, a breadboard for external components, and a compact USB instrument (oscilloscope, power supplies, waveform generator, digital I/O) connected to a laptop. A blinking LED relaxation oscillator demonstrates configuring on-chip transistors and observing internal waveforms, including hysteresis.
15:53 Design Cycle & Reconciliation: The Mosbius platform enables students to experience the full IC design cycle: conceive, simulate (using provided LTSpice library and models), fabricate (conceptually, via Mosbius), measure, and then reconcile differences between theoretical analysis, simulation results, and actual measurements.
18:11 Mosbius Chip Architecture: The chip acts as a "programmable transistor array," featuring various N and P transistors. Users can connect any of the 65 pins to 10 internal buses via 650 configurable transmission gate switches. This allows for flexible circuit construction, either internally on-chip or externally on the breadboard.
21:17 Component Selection: Mosbius focuses on providing on-chip MOS transistors (including matched pairs, current mirrors, operational amplifiers, and output stages) as they are harder to find off-chip. Resistors and capacitors are intended to be external components, preserving chip pins for transistor access.
24:08 Transistor Sizing Methodology: Devices are characterized by their GM over ID (transconductance over drain current) at a specific bias, promoting learning about relative sizing in analog design.
25:49 Design Accessibility: While the GDS layout (TSMC 65nm IO process) is proprietary due to NDAs, the Mosbius project provides detailed architectural information and an open-source SPICE library with models close to the actual chip, enabling accurate simulation.
33:23 Safety and Robustness: The chip features ESD protection and an on-board voltage limiter (2.5V VDD). It has shown significant robustness, surviving use in a lab with 100 students and tolerating accidental 5V inputs without failure.
42:01 Educational Resources & Kit Availability: A comprehensive laboratory manual is publicly available on mosbius.org, with solutions provided to instructors upon request. Approximately 150 kits are being produced for distribution to universities globally for fall semester courses.
44:11 Future Initiatives: Plans include organizing design contests (potentially lending kits for events), exploring mixed-signal integrations (e.g., pairing Mosbius with an FPGA), and considering a smaller version compatible with Tiny Tapeout's limited pin count.
50:24 Advanced Experiment: Delta-Sigma Converter: An advanced experiment demonstrates a first-order, one-bit delta-sigma analog-to-digital converter. The demo shows how the converter uses density modulation of ones and zeros to approximate an analog waveform and how noise shaping is visible in the frequency domain. This complex circuit uses nearly all Mosbius transistors and buses, highlighting the platform's capabilities for advanced learning.
58:24 Contact Information: Interested individuals can find more information and contact Peter Kingette via mosbius.org.