Would this JFET+op-amp circuit work?

This is Figure 9-3(b) from Motchenbacher - Low-Noise Electronic System Design, so I would expect it to work, but I don't understand it:

The addition of a discrete common-source stage at the input can offer lower noise. Overall negative feedback to the source of a common-source input stage, as shown in Fig. 9-3b, raises the amplifier's input impedance.

It seems like positive feedback to me:

1. Decrease in Vin →
2. Decrease in Vgs →
3. Decrease in Id →
4. Increase in Vd → (like a common-source amplifier so far)
5. Increase in Vo →
6. Increase in Vs →
7. Decrease in Vgs →
8. Decrease in Id →
9. ...

Am I missing something?

For comparison, here's another circuit that is similar, but looks like negative feedback, and has actually been built and works:

Edit:

So that picture is from the 1993 edition. I got my paper 1973 edition off the shelf (no Ctrl+F!), and the equivalent figure is 7-3(b), but with a BJT and the op-amp pins reversed:

Overall negative feedback to the emitter of a common-emitter input stage raises the amplifier input impedance.

This makes more sense to me. If the collector voltage tries to rise, the op-amp drops the emitter voltage to pull it back down and keep the collector at 0 V. So I'm thinking the first diagram is just a mistake.

• I think the top circuit will work if the transistor is carefully biased in such a way that the (AC) voltages across R(A) and R(D) are inverted in phase. That is exactly what a transistor is such a configuration is good at. The feedback is not through R(F) to IN+, but the transistor inverts the signal then applies to IN+. Apr 10, 2015 at 19:42
• I have not worked through the math, but this looks like a source bootstrapping circuit to me (reduces the effective input capacitance). The ratio of the resistances are going to matter. There's obviously some bias (the op-amp will rail as drawn) and maybe other stuff missing. Apr 10, 2015 at 20:01
• Just a question, what software is used to draw the second figure (the "another circuit")? Apr 11, 2015 at 14:47
– user16222
Apr 11, 2015 at 15:01
• Yes I believe the op-amp pins are just drawn backwards Jul 31, 2016 at 15:00