Back Andersson, Stefan

Emrich, Anders

Larsson-Edefors, Per

Ryman, Erik J

Ryman, Erik

Chalmers Publication Library

  1/1 
Correlator
8x2 8 CML
1:8 
LVDS
clk
8x2
signal
offset
Bias 
ctrl
data out
readout clk
readout enable
reset
correlator enable
Development of a Cross-Correlator System for Space-Borne Earth Observation 
Interferometric Imaging 
 
E. Ryman1, 2, A. Emrich1, S. Back Andersson1, P. Larsson-Edefors2 
 
1Omnisys Instruments, 2Chalmers University of Technology 
 
Synthetic aperture radiometry in the microwave region constitutes a new way of performing earth 
observation. Previously applied from a low earth orbit, there are now efforts being put into placing 
such an instrument in a geostationary earth orbit (GEO); this includes the geostationary 
atmospheric sounder (GAS) and the geostationary synthetic thinned aperture radiometer 
(GeoSTAR). These instruments will provide temperature and moisture distribution data from the 
atmosphere in a spatial and temporal resolution that was previously unattainable, due to cloud 
occlusion and large aperture requirements. A key component in these kinds of synthetic aperture 
instruments is the cross-correlator. 
 
A digital cross-correlator chip with 64 
inputs has been implemented in a 65-nm 
CMOS process. It performs pair-wise, one-
bit, zero-lag cross-correlation between all 
input signals. Tests have confirmed 
functionality at clock frequencies of at 
least 2.5 GHz. Power consumption has 
been measured to 0.13 mW/prod/GHz at 
nominal voltage. Radiation tests of the 
digital correlator chip have been 
performed at the Radiation Effects Facility 
at Texas A&M University. A variety of ion 
beams were used in a number of different 
testing scenarios to find weaknesses of 
the design, such as readout logic single 
event upsets (SEU) causing severe data 
corruption. Cross-sectional data from the 
radiation tests have been run through the Space Environment Information System (SPENVIS) to 
predict SEU behavior for GEO. An average SEU rate of ~1/day is expected when using 10 mm Al 
shielding. It is expected that errors in significant bits can be detected and discarded while less 
significant errors will be masked by integration. 
 
An 8-channel comparator chip, with the purpose of performing sampling of the analog input 
signals, has been implemented in a 130-nm BiCMOS process. Features such as core and output 
driver bias control have been included for performance/power consumption tuning. Clock return 
output, flip-flop sampling and current mode logic (CML) output drivers facilitate integration of the 
proposed correlator system, Fig. 1. Per-channel tuning pins are included for adjustment of input 
dc offsets. The comparator chip has been experimentally verified to perform sampling at a rate of 
at least 2.5 GS/s. 
 
The 64-input correlator system, currently under development, will bring together eight 
comparators and one digital correlator in a single unit. We expect that this correlator system will 
be working at 1 GS/s within a power budget of 2.5 W, making it well suited for space application. 
Fig. 1. Cross-correlator system schematic and die photos. 


Development of a Cross-Correlator System for Space-Borne Earth Observation Interferometric Imaging

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