Re: gEDA-user: A couple o' questions

[Bob Paddock <bob.paddock@xxxxxxxxx>]

On Saturday 08 April 2006 04:40 pm, John Doty wrote:

> > However, your other example of the op amp with the output grounded has
> > knocked me down. Very smart application!.
> 
> Ran into that one about 30 years ago when I was a grad student at  
> MIT. Mike Shao, another grad student (now Mr. Optical Interferometry  
> at JPL) had gotten a piezoelectric actuator driver from somebody but  
> couldn't figure out the strange topology, asked me to explain it to  
> him. Cascode transistors on the low voltage rails carried the current  
> out from the opamp to high voltage rails, where there were mirrors,  
> making a transconductance amplifier that had an output swing of  
> several hundred volts, just the thing to drive a piezo. I don't know  
> who came up with this.

While I'm sure Linear Tech. did not come up with, it is explained
here for anyone interested:

"How to Ring a Phone with a Quad Op Amp"

Summary:

http://www.linear.com/pc/downloadDocument.do?navId=H0,C1,C1003,C1042,C1031,C1061,P1266,D4338

Detailed description:

http://www.linear.com/pc/downloadDocument.do?navId=H0,C1,C1154,C1009,C1045,P1657,D4174