Radiant energy – Invisible radiant energy responsive electric signalling – Semiconductor system
Reexamination Certificate
1999-09-23
2001-10-30
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Semiconductor system
C250S370010, C250S370150
Reexamination Certificate
active
06310350
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to high resolution, broad band x-ray microcalorimeters and specifically to the electronic readout for these x-ray spectrometers.
2. Description of Related Art
When operated below 300 mK, cryogenic microcalorimeters offer nearly 100% efficiency between 100 eV and 10 keV and an energy resolution of a few electron volts. Currently available x-ray detectors cannot match such capabilities simultaneously. As a consequence, microcalorimeters are being used to improve the spectroscopy of astrophysical and laboratory plasmas as well as enhancing the sensitivity of present-day x-ray fluorescence methods for trace element determination in biological specimens, geological and environmental waste samples. This includes microanalysis using electron excitation in scanning electron microscopes, x-ray fluorescence using synchrotron radiation and proton excitation.
In a microcalorimeter, x-ray photons are absorbed and thermalized in a detector which is weakly coupled thermally to a cold bath. The rise in the detector's temperature as a result of the x-ray absorption is measured with a thermal sensor, producing an electrical signal that is proportional to the x-ray energy. For operation at temperatures below 4K these thermal sensors, or thermistors, take advantage of the strong temperature dependence of resistance in doped semiconductor crystals such as silicon or germanium. The electrical resistance of the sensor is determined by hopping conduction of free carriers, a process that is characteristic of doped germanium at cryogenic temperatures. See, U.S. Pat. No. 5,777,336.
The semiconductor thermistor used in such a microcalorimeter is impedance-matched to a JFET negative voltage feedback circuit. See, Silver et al. SPIE, Vol. 1159 at 423 (1989). An energy resolution of 5.9 eV at 1.5 keV and 7 eV at 6 keV has been achieved with neutron transmutation-doped (NTD) germanium-based thermistor technology. The thermalization time of the NTD-based detectors is about 10-20 &mgr;s and the thermal recovery time, ≦500 &mgr;s.
Up to now, a microcalorimeter has required a matching JFET preamplifier to operate successfully. There are many space-based and industrial applications that could benefit from operating multi-element arrays of these microcalorimeters. The corresponding number of preamplifiers and data processors could seriously drain available resources if the array consists of 50 or more microcalorimeters and their associated preamplifiers and data processors. Multiplexing a single JFET preamplifier among several microcalorimeters would be extremely advantageous in such cases.
SUMMARY OF THE INVENTION
In one aspect, the multi-element microcalorimeter array includes at least two microcalorimeters with each microcalorimeter including a detector coupled thermally to a cold bath. Each detector has a thermal sensor to generate a signal proportional to a rise in the detector's temperature. A single negative voltage feedback JFET preamplifier circuit is provided. This circuit includes a JFET with a gate, and the signals from thermal sensors are connected to this gate. The output of the preamplifier circuit is proportional to radiation energy absorbed by the detector. Each detector has a different thermal recovery time so that the individual detector channels may be identified easily.
In a preferred embodiment the thermal sensor is a thermistor which may be a neutron transmutation-doped (NTD) germanium-based semiconductor. Each thermistor is impedance-matched to the JFET preamplifier. It is preferred that each detector have fast thermalization times and high signal-to-noise ratios. The thermal recovery times of the detectors may be altered by the construction of the thermal link to the cold bath. It is also preferred that the signal from the thermal sensors be confined to frequencies in which Johnson noise predominates. The invention is particularly adapted for detecting x-ray energy.
It is, therefore, an object of the present invention to provide a method to multiplex one JFET preamplifier among several semiconductor-based microcalorimeters. The negative voltage feedback amplifier circuit offers the possibility to multiplex a single JFET between at least two detectors. Due to the virtual ground established by the negative feedback, more than one thermistor can be connected to the gate of the JFET without introducing cross-talk between the channels. The individual detector channels are identified easily by engineering the thermal recovery time to be slightly different for each detector channel. In general, the connection of multiple channels will increase the noise per channel as seen at the output of the JFET preamplifier. This potential noise increase can be overcome by using detectors with fast thermalization times and high signal-to-noise ratios. The signal of interest can then be confined to frequencies where the Johnson noise dominates and is controllable to a desired level. This multiplexing scheme makes it possible to reduce the overall number of preamplifier and post-processing channels for a large multi-element array. This reduction in turn significantly lowers the JFET heat load, mass and power requirements for the spectrometer array and is especially important for space-based applications where mass and power are at a premium. Where mass and power are not limited, the multiplexing scheme of the invention offers the opportunity to add more pixels to the array at no cost to the electronics and without jeopardizing the heat load and lifetime of the cryogen which forms the cold bath.
REFERENCES:
patent: 5777336 (1998-07-01), Silver et al.
Madden Norman W.
Silver Eric H.
Choate Hall & Stewart
Hannaher Constantine
Pasternack Sam
LandOfFree
Multiplexed microcalorimeter array does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Multiplexed microcalorimeter array, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Multiplexed microcalorimeter array will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2575595