CROSS CORRELATOR ASIC
Omnisys has implemented a high-speed, low-power cross-correlator ASIC in a 65-nm CMOS process. The ASIC will be used for synthetic aperture radiometry from geostationary orbiting earth observation satellites, providing a revolutionary lightweight and compact solution with an outstanding image quality.
The chip is based on a commercial 65-nm process technology with a 1.0-1.2 V nominal voltage range. It performs cross-correlation on all individual signal pairs from 64 digital 1-bit inputs which amounts to 2016 individual cross-correlation products. The experimental evaluation, using a specially developed PCB, demonstrates that the 3mm2 chip has a top performance of 3.6 GHz at a 1.2 V supply, at which it dissipates 790 mW. The layout uses both standard- and high-VT devices; the latter helps reducing standby power significantly. Neither the architecture nor the process is radiation hardened, but with technology scaling comes an intrinsical hardening. While the design will fail in the case of a hard error, a single-event upset, SEU, will not cause any major problem. In the event of an SEU, the bit flip is treated as noise during the integration or it will cause an unnatural spike, which is easily detected and removed in the resulting data.
- Observation in the microwave band traditionally requires heavy and bulky antennas with large aperture to achieve the required spatial resolution. Using synthetic aperture by interferometry can save both weight and space during launch.
- Using synthetic aperture interferometry will give the possibility of acquiring the entire image simultaneously which will improve image quality by avoiding time skew visible when using single dish scanning.
- Applying synthetic aperture radiometry using crosscorrelation in space requires great reductions in power dissipation and hardware size compared to the large ground-based correlators. Using process technologies in the sub-65-nm range makes it possible to fit a cross-correlator, with performance enough for synthetic aperture imaging from geostationary earth orbit, or GEO, into a single low-power ASIC.
MAIN APPLICATION FIELDS
For future improvements in weather forecasting and climatology, earth observation in the microwave band can give important information on temperature and humidity distribution. Performing microwave sounding from a GEO would give the additional advantage of continuous coverage of a large part of the earth surface, making it possible to study dynamic weather phenomena.