Sylvain Munaut Combines Two Tiny Tapeout Projects to Create an Open-Silicon Software-Defined Radio
While the resulting SDR won't be winning any awards for performance or features, it's a great example of Tiny Tapeout's flexibility.
Sylvain Munaut has created a basic software-defined radio (SDR) the hard way — by combining two open-silicon projects submitted for production on two Tiny Tapeout shuttle runs: an analog-to-digital converter (ADC) and a radio-frequency mixer.
"Tiny Tapeout allows anyone to easily design custom silicon using the SKY130 Open-PDK and get it taped-out at low cost by combining hundreds of projects on the same chip," Munaut explains of Matt Venn's project for ultra-low-cost integrated circuit production. "On the Tiny Tapeout 6 shuttle, Carsten Wulff taped out an eight-bit SAR [Successive Approximation] ADC. And on the Tiny Tapeout 7 shuttle, Kolos Koblász taped out an RF mixer. I decided to combine both of these, a Glasgow [Interface Explorer] USB interface, and some GNU Radio software to build a small demo SDR!"
Venn's Tiny Tapeout, covered in more detail here, is designed to lower the barrier to entry in the chip design field by making it possible to have your own design fabricated as a silicon chip for as little as a hundred dollars — by breaking a single chip down into tiles and allowing dozens or hundreds of designs to coexist side-by-side. Now into its tenth production run, Tiny Tapeout's sixth run saw a major breakthrough for the project: its first support, since expanded, for analog and mixed-signal designs.
Taking advantage of this newly-added support, Carsten Wulff submitted a modified version of a SAR ADC he designed a few years earlier for a newer process node — and was followed by Kolos Koblász who submitted an RF mixer design for the seventh production run. The two designs are separate, but coincidentally compatible: "It just so happens that the ADC has a differential input," Munaut explains, "and the RF mixer has a differential output — so it's almost like they were made to be connected together."
Taking advantage of this happy accident of chance, Munaut combined chips from Tiny Tapeout 6 and Tiny Tapeout 7 — which provide anyone with full access to any of the projects submitted for production during that run — and adapted them into a basic software-defined radio, using a Raspberry Pi RP2040 microcontroller on the chips' carrier boards and a Glasgow Interface Explorer to provide a USB interface compatible with the GNU Radio software.
The project is documented in the video embedded above and on Munaut's YouTube channel; more information on Tiny Tapeout is available on the official website.