513 Tetrahedral Oscillator
513 : Tetrahedral Oscillator
- Author: Juvenal Romero Pedraza, Gael Gabino Diaz Ojeda, Mario Ranferi Romero Salgado.
- Description: Tetrahedral oscillator based on coupled CMOS inverter pairs with capacitive load tuning.
- GitHub repository
- Open in 3D viewer
- Clock: 0 Hz
How it works
This project implements a compact tetrahedral-style oscillator in SKY130 for the Tiny Tapeout analog flow. The circuit is built as a semi-custom Magic layout using SKY130 standard-cell inverters and buffers as the active devices, with MIM capacitors used as distributed load elements.
The oscillator is inspired by the tetrahedral oscillator concept described by
Richelle L. Smith and Thomas H. Lee. This implementation is adapted to the
Tiny Tapeout 1x2 analog layout template and uses four buffered observation
nodes routed to uo_out[0] through uo_out[3].
The design uses the 1.8 V supply domain:
VDPWR: 1.8 V supplyVGND: grounduo_out[0]touo_out[3]: buffered oscillator observation outputs
How to test
Power the design from VDPWR = 1.8 V and VGND = 0 V. Observe
uo_out[0] through uo_out[3] with a high-impedance oscilloscope probe or a
frequency counter input that does not overload the output drivers.
Post-layout extracted simulation was run with Magic extraction and ngspice.
The PEX testbench is in tb/tt_um_tetrahedral-oscilator_pex_tb.spice, and it
saves the four output waveforms as uo_out_0, uo_out_1, uo_out_2, and
uo_out_3.
The measured post-layout transient waveforms oscillate around the 1.8 V logic range. A frequency near 12 MHz is practical to measure with standard university lab equipment such as a 50 MHz or 100 MHz oscilloscope, provided the output is probed with a high-impedance probe.
Tooling extensions (non-invasive)
To improve observability and reproducibility without altering the validated layout collateral, this project documents and uses additional support tooling:
- GDS2WebGL (
https://github.com/s-holst/GDS2WebGL) as a browser-based GDS visualizer flow for interactive inspection. - png2layout (PNG-2-Layout) to convert transparent PNG images into Manhattan-clean pixelated GDS shapes with DRC-oriented cleanup.
- sky-flow (sky130-flow-gui) to automate PDK and VLSI software setup, create specific route recipes, run ngspice simulations, inspect waveform results, and provide extra numerical/flow utilities.
These tools are treated as complementary infrastructure around the project and not as replacements for the documented Tiny Tapeout handoff artifacts.
External hardware
No external passives or bias sources are required. Use standard 1.8 V power and high-impedance probing on the output pins.
IO
| # | Input | Output | Bidirectional |
|---|---|---|---|
| 0 | osc_out_0 | ||
| 1 | osc_out_1 | ||
| 2 | osc_out_2 | ||
| 3 | osc_out_3 | ||
| 4 | |||
| 5 | |||
| 6 | |||
| 7 |