Digital Cross-Correlation At 250 Mhz Using High-Performance Fpga'S

This paper describes a 250 MHz cross-correlator for radio astronomy built using field-programmable gate arrays (FPGA's). Experimental results indicate that CMOS FPGA's can operate reliably at 250 MHz, Long-term integration tests of up to 10(12) samples have been taken, demonstrating the correlator accuracy down to the limits of the testing apparatus. Recent estimates indicate that higher-performance FPGA's available early in 1998 can attain speeds of over 300 MHz using 20% fewer logic elements than previous designs. The FPGA correlator can be reconfigured for 2, 3, 4, or even 9 levels of sensitivity, permitting a tradeoff of the number of lags with the sensitivity desired.Although FPGA's have historically been more expensive than custom chips, starting this year FPGA correlators are actually less expensive than custom correlator chips. This cost reduction is due to the fact that FPGA's are standard components in the electronics industry and are produced in much higher volumes than custom correlators. As an example, a 1024-lag 4-level cross-correlator can be produced for an FPGA chip cost of less than $80 in 1998. FPGA's continue to drop in price faster than custom devices because volumes continue to increase and FPGA architectures continue to improve. The demonstrated high performance of FPGA's coupled with their extreme flexibility, reconfigurability and lower cost make FPGA's ideally suited for the next generation of large correlator arrays.