[sdiy] JFET input protection

[Scott Nordlund]

> Hi
>
> What kind of protection is required for inputs that have discrete jfet as
> the buffer? Is simple series resistor enough or do I need to add
> zener diodes? (with the increase in nonlinear input capacitance)
>
> Antti

ESD is typically a very small charge at high potential.  A JFET has quite
high gate impedance, so very high voltages can build up and ruin things.
I think a resistor will not help much as it will only slow the charge
in an insignificant sort of way.  A series resistor, capacitor and 
resistor to ground would probably help (and also likely defeat the 
purpose of using a JFET).  A series resistor and clamping diodes might be
best.  The gate should be able to tolerate voltages significantly beyond
the power supply rails (unlike an IC), so this may give you a little
freedom to choose diodes that have small capacitance but high voltage
drop, or something like that.

As always, if you know better, feel free to correct me!
 		 	   		  
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