I am planning to do a preamplifier opamp style with dual FET input.
I would like to use MOSFET ZVN3306A.
My question is how low current I should be able to run in the MOSFET pair?
For a good result.
For a starter I have a schematic using 10mA per FET.
Is this enough?
Are there any better MOSFETs to use?
For lower currents.
I would like to use MOSFET ZVN3306A.
My question is how low current I should be able to run in the MOSFET pair?
For a good result.
For a starter I have a schematic using 10mA per FET.
Is this enough?
Are there any better MOSFETs to use?
For lower currents.
I'd guess the reason for running at 10mA would be to get sufficient gm. If you want to run lower then presumably you'd be looking for a FET with higher gm.
Balanced against that desire for higher gm for an input stage FET you'd probably want as low input capacitances as you can manage. This dual FET from Diodes looks about as low as I've seen in discrete FETs for capacitances, it also looks as though its gm is quite a bit better than the 3306. Its only 20V though : https://www.diodes.com/assets/Datasheets/ds31481.pdf
Ah I see the package is not at all suitable for DIY, way too tiny. What a pity.
Balanced against that desire for higher gm for an input stage FET you'd probably want as low input capacitances as you can manage. This dual FET from Diodes looks about as low as I've seen in discrete FETs for capacitances, it also looks as though its gm is quite a bit better than the 3306. Its only 20V though : https://www.diodes.com/assets/Datasheets/ds31481.pdf
Ah I see the package is not at all suitable for DIY, way too tiny. What a pity.
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Thanks.
The reason I want to try this is that OPA2134 has FET input.
It is not the same as JFET input.
But for chips as OPA2134 they they have very small FETs with good data at low current.
I should inform that I am looking for best TO-92 transistors.
I will not go into SMD SOIC for time being.
The reason I want to try this is that OPA2134 has FET input.
It is not the same as JFET input.
But for chips as OPA2134 they they have very small FETs with good data at low current.
I should inform that I am looking for best TO-92 transistors.
I will not go into SMD SOIC for time being.
I looked around for something in a larger package - this one from Toshiba I have managed to DIY with, its 1.6mm long and has very good gm for a MOSFET (even a gm plot for the relevant currents, starting at 1mA) : https://toshiba.semicon-storage.com/info/docget.jsp?did=11219&prodName=SSM3K35FS
I just read your note on TO-92s. I'm not aware of anything in a leaded package which comes close in performance to these Toshiba SMTs.
I just read your note on TO-92s. I'm not aware of anything in a leaded package which comes close in performance to these Toshiba SMTs.
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