PhD orals on Photoelectronic Analog to Digital Conversion, 10 am Thu Dec 6th, CIS-X 101

Rafael Aldana raldana at
Mon Dec 3 16:11:08 PST 2007

Department of Electrical Engineering
Stanford University
CIS Extension Auditorium
Thursday, December 6th 2007 10:00- 11:00 am
Refreshments: 9:45 am

Miniaturization has primarily benefited digital, rather than analog,
electronics both in terms of speed and cost. This has led to an increasing
need to convert analog signals to digital at high speed. Historically this
Analog to Digital Converters and other information encoding systems were
based in electron beam deflection, in the form of oscilloscopes and cathode
ray tubes; but inherent limitations due to price, size and versatility made
them, if not obsolete, at least far less common than in previous ages.
Recent advances in microfabrication seem able to make these systems attain
performances comparable, if not better than those of their replacements.
In this work we present one of such a miniaturized system, a Niquyst rate
analog to digital converter, and establish the fundamental and practical
limits of its performance. For that purpose we built an electron beam based
analog to digital converter with sampling rate of 3GHz and 5 bits of
resolution. In it, a pulsed electron beam is swept through a set of
deflection plates to which the analog signal is fed; the lateral deflection
imparted by the plates is proportional to the signal to be sampled. The
electron bunches travel through a field free region and hit a
Metal-Semiconductor-Metal detector column at a position that determines the
digital code.
The system has two characteristics that make it a great candidate for fast
ADCs: the use of a pulsed electron beam, resulting from a low jitter
mode-locked laser illuminating a photocathode; and the use of spatial
quantization. The main advantage of the proposed system is its versatility,
given by the use of multiple electron beams generated using a photocathode
illuminated by laser pulses staggered in time, the deflection of all
multiple beams with a single set of traveling wave plates, and the use of
detector columns with variable detector configurations.

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