Sigma didn’t like the image quality results produced by the California-based Foveon subsidiary, so it pulled the plug on its eagerly-awaited full frame stacked sensor camera. That decision took guts (and private ownership). We now learn from a video released at the CP+ (Japanese) conference that the specific problem appears to have to do with the lack of an on-chip analog-to-digital converter (ADC) and power supply.
Sigma indicated it would start from scratch, and that the scratch start would happen in Japan rather than in the US.
The ADC issue was a big deal five or six years ago, when Sony sensors had adapted on-chip ADCs. Since Sony made sensors for most of the other full frame camera producers, including Nikon, only Canon was left with off-chip ADC processing, and the higher read noise associated with it. Many teeth gnashed and hands wrung in online fanboy debates about image quality. It all died down with the release of the Canon 5D Mark IV, which finally showed Canon had mostly caught up.
The Foveon folks don’t appear to have been taking notes. To be fair, the progress in image quality across the industry over the past five years has been remarkable, and designs originally intended to be released a year ago didn’t have quite such a high bar to top. Back when Sigma hired another California firm to produce the sensors, it may be that the image quality baked into the design would be enough to carve a market out from the then-popular Sony A7 II and canon 5D Mark IV.