Low Power Digital Correlator System for PATH Mission

The NASA's PATH mission employs GeoSTAR spectral radiometer processing data from antenna consisting of three arms, each holding 128 microwave receivers. Each of the 384 receivers amplifies RF signals, and down-converts them to an intermediate frequency (IF). As a result, 768 in-phase (I) and quadrature (Q) signals are produced with a frequency of 10 to 500MHz. The IF signals have to be normalized and digitized with 1Gs/s sampling rate for further cross-correlation. Each signal from one arm of the receiver must be cross-correlated with all signals from the other two arms, therefore a system containing 196,000 parallel cross-correlation blocks is needed. Since the GeoSTAR is a space born instrument, low power dissipation and ensuring system reliability, through processing redundancy, are one of the most important requirements. A system assembled by using off-the-shelf components would be extremely power inefficient, bulky, and unreliable. Therefore, a system that is based on application specific integrated circuits (ASICs) is required. While working on the NASA's SBIR Phase II project "Low Power Cross-Correlator ASIC" (NNX13CP01C), Pacific Microchip Corp. has developed and fabricated an ASIC that includes 128-element array of 2-bit 1GS/s ADCs, and 4096 parallel cross-correlation cells. The ASIC was designed based on the GeoSTAR radiometer requirements, therefore it is intended to be the key component in the cross-correlator system which is being developed. The system will contain means correlation results further post-processing and control of ASICs.