Hi all,
I need to design a current source that will charge a capacitor, because the capacitor is very small( about 0.7 pF) I need a 1-10 nA current source, somebody can help me, and suggest how I can design such current source?
The circuit I'm designing measures changes in MEMS capacitor.
P.S
I need linear charge of the capacitor, so I need constant current source.
Well, you'll find that 10Ghm: resistors are about as rare as 700 femtofarad capacitors.
Are you pulling our legs? linear charging a 700 fF cap?
Sensitive to non-linear charging is it?
It just needs a few electrons!
Seriously, I would suggest attaching a larger .01uF or so capacitor in parallel with the tiny cap. Charge them both with the manageable constant current, then disconnect the larger cap. Use a connection smaller than a gnat's eyelash.
Any current source that I can imagine will have at least a few picofarads of stray output capacitance. You will have to periodically discharge the capacitor, and that switch adds more stray capacitance.