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Old 20th January 2010, 02:36 AM   #1
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Default Matching Jfets

I am matching Jfets (J74/K170) with a curve tracer.

When matching same channel Jfets for preamp, should I choose closest Idss or closest gradiant pairs?

What about matching N-P channel Jfets?

Thanks
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Old 20th January 2010, 07:14 AM   #2
h_a is offline h_a  Europe
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I could imagine that in a differential pair closest gradient could be better, but without checking it with a distortion analyzer we will never know.

Don't expect too much from matching, the very most people are happy with IDSS-sorted jfets.

N to P matching is usefull to lower offset, but with respect to distortion cancellation I never had the time to test it, but I'm still thinking of it.

Have fun, Hannes
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Old 20th January 2010, 01:58 PM   #3
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Thank you, that's what I think too. Matching uses up a lot of time but the result is still ????
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Old 20th January 2010, 02:08 PM   #4
AndrewT is offline AndrewT  Scotland
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closest gradient over the SAME current range.
That requires the gradient to be measured at fixed matching currents.
How do you do that at a fixed and repeatable Tj?

The above condition virtually demands selecting the same Idss to yield the same gradient at a lesser operating current.
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