For many purposes the Source and Drain are interchangeable and if you flip an FET it will still mostly work.
really? can you post some example FET? all i know is nFET and pFET which i dont believe work the way you've stated. the 2 way transistor that i know but never used is triac?
This is right, Shafri!
For most of the J-FETs, the channel construction is exactly the same for its Source and Drain ends.
For example, see the BFJ309 (an N-Ch UHF RF amplifier JFET in SOT-23 package) with the marking '6U' (the
MMBFJ309LT1 actually) the DS1000 has in the front-end as a mixer/amplifier of the DC and the AC components of the under-test signal.
Though the pins of that JFET are 1=Drain, 2=Source and 3=Gate, in the
DS1000 schematics I have posted it can clearly be seen that, though in the Ch1 (and Ch2) analog front-end schematic sheet it is biased "correctly" (with pin 2 as Source and pin 1 as Drain), in the Trigger Input Front-End it is NOT(!), with pin 2 acting as the Drain and pin 1 as the Source. Yet, the device works fine!
And this is not a schematic's typo, since that strange biasing of the specific component can be confirmed in any of the high resolution PCB pictures available of the DS1000.
Actually, just read the first feature of that component, in the On-Semiconductor datasheet posted above in page #1, clearly stating that:
"
Drain and Source are Interchangeable"
EDIT:
The same exactly states Fairchild (as a fourth feature) for their version of
BFJ309!
-George