What sort of devices are used in applications such as creating a 1nA current source?
Most transistors (both bipolar and JFET) that I find enter cutoff at this level. collector cutoff current of the analog devices MAT02 matched NPN BJT pair is 3nA (these things cost 20 bucks a pop)
IDoff of the J113 JFET is 1nA
a circuit with extremely high gain in a feedback configuration might be able to hold these devices on the edge of cutoff to make them source such low currents, but are there [discretely packaged] devices available for extremely low current applications?..I'm having a bear of a time finding any
EDIT: its also rare that datasheets spec devices down to such low levels, or even provide any information at such low levels. I'm not sure if I fully trust the SPICE2 models for these devices either, at low levels.
Most transistors (both bipolar and JFET) that I find enter cutoff at this level. collector cutoff current of the analog devices MAT02 matched NPN BJT pair is 3nA (these things cost 20 bucks a pop)
IDoff of the J113 JFET is 1nA
a circuit with extremely high gain in a feedback configuration might be able to hold these devices on the edge of cutoff to make them source such low currents, but are there [discretely packaged] devices available for extremely low current applications?..I'm having a bear of a time finding any
EDIT: its also rare that datasheets spec devices down to such low levels, or even provide any information at such low levels. I'm not sure if I fully trust the SPICE2 models for these devices either, at low levels.
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