Do you really need to Match SMD JFETs?

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Do you really need to Match SMD JFETs?

Postby Jcknowles89 » 03 Jul 2019, 16:18

Hey all,

about to start building a Phase 90. Was doing some research and from what I saw the type of JFET used to Bias the Op amp phase shifters doesn't matter as long as they're matched (correct me if I am wrong on this). I normally try to use SMD JFETs in most of my builds (MMBFJ201 or MMBF5457) just because they are easier to get a hold of. I have also heard that SMD JFETS have significantly better Tolerances and don't necessarily need to be Matched? Anyone confirm this?

Thanks,
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Re: Do you really need to Match SMD JFETs?

Postby Dirk_Hendrik » 04 Jul 2019, 14:59

I would not dare to blatantly confirm. But my own experience is that when I use JFEt's that come from the same reel there's very little difference. First, and only, time I did JFET matching I got such identical results I started to doubt my setup.
Sorry. Plain out of planes.

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Re: Do you really need to Match SMD JFETs?

Postby julessouren » 07 Jul 2019, 19:44

Just my 2 inexperienced cents, but I believe the actual wafer production quality is independent of the device packaging.

So, you might have a big wafer of transistors, being cut up into individual dies. Depending on performance or spec, they might bin or name the parts differently, but nothing has changed in the wafer production process when going from rather obsolete THT TO-92 packaging to modern SMD SOT-23 packages.

In other words, the individual fets on the wafer still have a (too) wide parameter spread, just as much with SMD devices as with THT devices.
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