Patent Number: 047773626
Section: summary

TECHNICAL FIELD The invention relates generally to devices which characterize the effect of particle bombardment on electronic circuits or devices. In particular, the invention relates to devices for measuring extremely fast electrical waveforms produced when an atomic or subatomic particle strikes an electronic circuit or device. BACKGROUND OF THE INVENTION Atomic and subatomic particles, such as alpha particles, are constantly streaming through the universe and striking objects at random intervals. While more frequent in outer space, many of these particles exist in earth's atmosphere as well. When such a particle strikes a sensitive electronic circuit, it can generate unwanted electron-hole pairs which can upset the operation and output of the circuit. Either or both of two techniques can be used to accommodate these particles. First, the circuit can be shielded. This is not entirely satisfactory since a shield will stop only those particles having less than a certain energy level. Second, the circuit can be designed so as to compensate for the particular electrical waveform which a particle causes. This technique has not been completely satisfactory because the waveforms, which typically have rise times on the order of 5 picoseconds, are too fast to measure with today's technology. However, there have been recent advances in devices which can sample picosecond waveforms. These devices have almost exclusively used Josephson junctions to perform the sampling and have time resolutions that today approach 2 picoseconds. So far, Josephson samplers have mostly been used to investigate electrical waveforms of circuits on the same chip and in the same cryogenic environment as the samplers. Apparatus and techniques to allow connection of a Josephson sampler to an external environment without degrading the resolution of the sampling are now being made available as sampling applications have increased. With the advent of picosecond samplers, a controlled test environment can be established to methodically inject atomic or subatomic particles onto an electronic circuit or device. The resultant electrical waveforms produced by the bombarded electronic device can then be measured with high resolution and the electronic device can thus be re-designed for compensation. Control of the characteristics of the injected particles, such as, particle type, velocity, and angle of incidence, allows an electronic circuit or device to be tested and designed for a particular application whether in space or on earth. SUMMARY OF THE INVENTION The foregoing problem is obviated by the present invention which comprises: Apparatus for measuring the electrical waveform generated by an atomic or subatomic particle incident on an electronic device, comprising: means for detecting the incidence of the particle on the device a first time interval before the particle strikes the device; means for sampling a point on the said waveform at a second time interval following detection of the incidence of the particle by the means for detecting; and means for moving the sampling point timewise along the said waveform during succeeding particle incidences so that the means for sampling measures the entirety of the said waveform. The means for detecting is chosen to have as small an effect as possible on the path and energy of the particle, so that the particle will strike the device under test in substantially the same manner as it would in actual operation. Alternatively, the means for detecting should have a predictable effect on the path and energy of the particle so that such effect can be countered later on. After the electrical waveform is sampled at one point, the invention continues to detect succeeding particle strikes which, under controlled conditions, produce the same electrical waveform. Thus, the invention can sample different points of the waveform until the entire waveform is measured. It is advantageous to average several samples at each point in order to reduce the effects of noise and the like.