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Receivers Unlimited Technology
A Brief History of Time Variant Technology
Physicists involved in nuclear and particle physics research have been working on improving the detection and processing of photons in capacitive detectors for almost 50 years. To make accurate measurements of detected photons, it is very important to reduce noise from the preamplifier electronics. In the end, physicists have the same problems as optical receiver designers, they need to improve the signal to noise ratios for detected current pulses. Since the founders of Receivers Unlimited were physicists involved in radiation detection, it is possible to build on this technology base.
Starting in the 1960s and early 70s there was considerable interest in nuclear radiation detection. Articles such as "Signal to Noise Ratio in Nuclear Pulse Amplifiers with High Repetition Rates" appeared as early as 1966. By 1982, the state of the art had advanced to time variant integrators and amplifiers. "Gated Integrators" were commercially available and Nuclear Instruments and Methods included articles such as, "Signal Evaluation in Multielectrode Radiation Detectors by Means of Time Dependent Weighting Vector".(Here, a "weighting vector" would be called a transfer function in optics.)
Over several decades, the physicists involved in nuclear radiation detection had analyzed the problem of charge deposited at a high rate on a capacitive detector and arrived at the optimum solution for signal to noise. That optimum solution is no longer debated, it is simply a matched filter implemented by time variant electronics.
Receivers Unlimited
Receivers Unlimited has built on these decades of research in nuclear radiation detection and applied these principles to detection of communication signals. The optical communications signals consist of current pulses deposited in capacitive detector - a situation very similar to nuclear radiation detection.
There are 3 advances from nuclear radiation detection that can be directly applied to optical receiver(TIA) design:
1. Time domain models to allow simplification of noise and filtering analysis.
2. Time domain analysis leads to obvious identification of matched filter.
3. Matched filter can be optimally implemented in time variant circuits.
Finally, it is possible to build on and improve upon 50 years of nuclear radiation detection, because optical communication current pulses are subject to one constraint that nuclear radiation is not subject to:
4. The arrival time of each communication pulse is known in advance.
As a result, the time variant designs from Receivers Unlimited actually improve upon the state of the art in nuclear radiation detection
Summary
Receivers Unlimited is able to apply the nuclear radiation detector analysis and results to optical communications. In addition, Receivers Unlimited has intellectual property that enhances TIA performance over the basic nuclear detector results.
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