Other
Scientific paper
Jan 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007esasp.643..231a&link_type=abstract
Workshop on Dust in Planetary Systems (ESA SP-643). September 26-30 2005, Kauai, Hawaii. Editors: Krueger, H. and Graps, A., p.2
Other
2
Scientific paper
Solar UV radiation and solar wind, which give cosmic dust grains their charges, can also interfere with the in-situ measurement of those dust charges. They can generate small currents, equivalent to detector leakage currents, which are collected on the sensing electrodes of a dust charge detector. They increase the noise of the detector and can drive it into saturation. In order to safely discharge the currents, a new charge-sensitive amplifier (CSA) has been developed using a double-gate junction field-effect transistor (JFET), a low-leakage input protection diode, and a second feedback loop. Positive currents are safely discharged via the JFET's first gate(G1)-to-source junction, while negative currents are discharged via the protection diode. The currents generate a low-amplitude, low-frequency bias voltage at G1, which would drive a conventional JFET into saturation. To compensate for the bias voltage at G1, a low-frequency baseline-restorer-type feedback loop generates another bias voltage, one that controls the JFET's second gate, G2, in such a way that the JFET is always operating in its optimum range. This CSA does not require an input capacitor or a feedback resistor, which would generate their own noise and thereby increase the overall noise of the CSA. A CSA lab model with these features has been built and tested. Its noise is <100 electrons (rms) in a frequency band from 10 kHz to greater than 10 MHz at room temperature and at a detector capacitance of 5 pF.
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