JFET Common Source DC Amplifier Temperature Compensation

[Vladimir Vassilevsky]

D from BC wrote:

What are some ways to temperature compensate a common source JFET DC
amplifier.

Vdd=5V
|
10K
|
+------------Vout (biased for 50% Vdd)
|d
signal--->[ N JFET
|s
|
Gnd

Here we go:

http://www.abvolt.com/misc/jfet2.gif

Paycheck time

Neato!

DC amp: check
Thermal compensation: check
BW to 2Mhz: check (Looks fast! (1) (2))
Amplifies below rail voltage: check
Inverting output: n/a check
Uses matched dual JFET pack: check
Low noise: op amp noise introduced (eh...might be ok).. check
Parts count: great
Prone to oscillation: dunno yet

(1) No gain!
(2) I suspect thermal compensation can be traded off for more gain by
including negative feedback about the op amp.

Added two resistors. Now there is gain.

http://www.abvolt.com/misc/jfet_3.gif

In some ways this circuit is like the inclusion of Rs... Gain is
traded off for thermal stability.

This schematics is a sort of the differential amplifier.

Impressive

Sure, as I always do.


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com