I have a depletion mode Fet Rf preamp circuit, the circuit appears to be unbiased.
Here (half way down the page):
http://www.vlf.it/fritz/pocketrx.html
I get the 680k inline with the gate, its a Rc lowpass in conjunction with the gate capacitance.
I dont get how this works bias wise, the gate needs to be for this Fet about 2 volts lower than the drain to be in the linear region, but the drain is grounded, so is the unused dual gate, and the input gate is too through a big resistor, to me this Fet is just going to pass its Idss and stay there, unless either its some kind of grounded gate amp with no bias or it relies on the Rf being high enough voltage tp overcome the gate threshold, which I doubt it will esp with Vlf signals which will be uV.
Any ideas?
Edit: Answered my own question, a jfet can only operate with a negative bias, and I assumed the Bf966 is a Jfet, its a dmos Fet and can work with very small amounts of positive bias.
Here (half way down the page):
http://www.vlf.it/fritz/pocketrx.html
I get the 680k inline with the gate, its a Rc lowpass in conjunction with the gate capacitance.
I dont get how this works bias wise, the gate needs to be for this Fet about 2 volts lower than the drain to be in the linear region, but the drain is grounded, so is the unused dual gate, and the input gate is too through a big resistor, to me this Fet is just going to pass its Idss and stay there, unless either its some kind of grounded gate amp with no bias or it relies on the Rf being high enough voltage tp overcome the gate threshold, which I doubt it will esp with Vlf signals which will be uV.
Any ideas?
Edit: Answered my own question, a jfet can only operate with a negative bias, and I assumed the Bf966 is a Jfet, its a dmos Fet and can work with very small amounts of positive bias.
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