odd JFET configuration

Question

I was looking at figure 33 of the OP77 datasheet, and the JFET labeled D2 has an odd connection. Based on the way the circuit works that JFET must be a diode right? So why is the JFET connected as it is in the figure?

I thought this was a duplicate (http://electronics.stackexchange.com/questions/16966/transistor-as-low-leakage-diode/) But now I see that question asked about the BJT, while your question asks about the JFET. — The Photon, Mar 27 '13 at 20:53

score 7 · Accepted Answer · answered Mar 27 '13 at 22:31

7

The JFET is acting as a diode. So why not just use a diode? The main reason for using a JFET as a diode is that it has low leakage compared to ordinary diodes.

answered Mar 27 '13 at 22:31

Kaz

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any recommendations on a SMD or through hole JFET that would work? – David Mar 27 '13 at 23:02

score 2 · Answer 2 · answered Mar 27 '13 at 21:55

2

It is acting like a diode. Because the circuit in question is an absolute value amplifier it has to handle positive signal excursions differently to how it handles negative signals because basically it's a precision full-wave rectifier.

answered Mar 27 '13 at 21:55

Andy aka

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odd JFET configuration

2 Answers2