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Ultralow-Power Digital Correlator for Microwave PolarimetryA recently developed high-speed digital correlator is especially well suited for processing readings of a passive microwave polarimeter. This circuit computes the autocorrelations of, and the cross-correlations among, data in four digital input streams representing samples of in-phase (I) and quadrature (Q) components of two intermediate-frequency (IF) signals, denoted A and B, that are generated in heterodyne reception of two microwave signals. The IF signals arriving at the correlator input terminals have been digitized to three levels (-1,0,1) at a sampling rate up to 500 MHz. Two bits (representing sign and magnitude) are needed to represent the instantaneous datum in each input channel; hence, eight bits are needed to represent the four input signals during any given cycle of the sampling clock. The accumulation (integration) time for the correlation is programmable in increments of 2(exp 8) cycles of the sampling clock, up to a maximum of 2(exp 24) cycles. The basic functionality of the correlator is embodied in 16 correlation slices, each of which contains identical logic circuits and counters (see figure). The first stage of each correlation slice is a logic gate that computes one of the desired correlations (for example, the autocorrelation of the I component of A or the negative of the cross-correlation of the I component of A and the Q component of B). The sampling of the output of the logic gate output is controlled by the sampling-clock signal, and an 8-bit counter increments in every clock cycle when the logic gate generates output. The most significant bit of the 8-bit counter is sampled by a 16-bit counter with a clock signal at 2(exp 8) the frequency of the sampling clock. The 16-bit counter is incremented every time the 8-bit counter rolls over.
Document ID
20110020422
Acquisition Source
Goddard Space Flight Center
Document Type
Other - NASA Tech Brief
External Source(s)
http://www.techbriefs.com/component/content/article/721
Authors
Piepmeier, Jeffrey R. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Hass, K. Joseph (Idaho Univ. Moscow, ID, United States)
Date Acquired
August 25, 2013
Publication Date
August 1, 2004
Publication Information
Publication: NASA Tech Briefs, August 2004
Subject Category
Man/System Technology And Life Support
Report/Patent Number
GSC-14746-1
Distribution Limits
Public
Copyright
Public Use Permitted.

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IDRelationTitle20110020405Collected WorksNASA Tech Briefs, August 2004
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