# Re: Interesting negative capacitance circuit

• posted

It looks like something related was granted in 2012, but its fee status

>is listed as "Lapsed" ;-) > >

Nope. Go thee unto: and scroll down to the bottom under "Legal Events". Fees were paid on July 4, 2014 (does the patent office really work on July 4th?). On Mar 22, 2016, it looks like Intersil changed patent attorneys and ownership was transfered. Looks very much alive to me, although still an application.

```--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com ```
• posted

Nonsense. Show us how you analyzed it.

Bypassing the resistor makes it NOT-LIKE a current source.

Bull-crap! My analysis assumed infinite.

I was fortunate enough to have Harry B. Lee for circuit analysis because I was in the Honors EE program. Thus I didn't have to endure the Guillemin nonsense... so I'm quite comfortable doing nodal and loop analyses.

I suggest you study up ;-) ...Jim Thompson

```--
| James E.Thompson                                 |    mens     |
• posted

You assumed the admittance of the right current source was infinite, i.e. a dead short? Well...

It looked to me like the analysis was along the lines of the loop analysis for a diff-pair with a current source in the tail. With a DC-coupled diff-pair drawing say 2mA and a common mode signal, both inputs go up, and the current source draws 2mA. In differential mode one transistor decreases conductance to 1.9mA, the other increases to 2.1mA, and the current source draws...2mA. Its conductance never changes.

If the source's conductance never changes with signal, then from a small signal AC analysis perspective it's fine to treat it as if it has an infinite real impedance (zero admittance.) It's just a DC source.

My point of contention is that it looks like in this circuit the conductance of the right current source must vary with signal. If it does that, then the magnitude of its admittance must be finite, in which case it can't have a infinite (real) impedance.

Who's Guillemin, this guy?

• posted

"NegativeCapacitor.pdf" on the S.E.D/Schematics Page of my website has been updated to include simulations showing the regions of instability. ...Jim Thompson

```--
| James E.Thompson                                 |    mens     |
• posted

Infinite IMPEDANCE

You are hand-waving instead of analyzing. You apparently have no clue how to do small-signal AC analysis.

I have reposted my NegativeCapacitor.pdf...

"NegativeCapacitor.pdf" on the S.E.D/Schematics Page of my website has been updated to include simulations showing the regions of instability.

For amusement I will also do the simulations with ideal devices and see what results.

Nope... ERNST Guillemin. ...Jim Thompson

```--
| James E.Thompson                                 |    mens     |
• posted

Small-signal AC analysis is based on a set of assumptions, and my point is that I'm not sure that considering the rightmost current source to have infinite real impedance for AC is a valid assumption. I'm willing to concede that I'm wrong, but I'd like to know why.

Much appreciated.

• posted

"NegativeCapacitor.pdf" on the S.E.D/Schematics Page of my website has been further updated to include simulations using ideal active devices.

With RIN = 0, you can obtain a perfectly ideal negative capacitor.

Ideal devices can be closely approximated on an integrated circuit, thus explaining why the patent has been revived. ...Jim Thompson

```--
| James E.Thompson                                 |    mens     |
• posted

It'll appear in parallel with re2 in a small-signal analysis. If it's large compared to re2 it's effect will be negligible.

Done. See..

Message-ID: ...Jim Thompson

```--
| James E.Thompson                                 |    mens     |
• posted

I did do an analysis without making the assumption that the AC impedance of the right current source is infinite, and yes it does appear that in the limiting case it reduces to the equation given in the patent. A legible version will have to wait until I pick up more graph paper...;-)

• posted

Those skilled in the art will recognize the equations (in the patent) just above and just below [0028], match my derivation, if you make the identity substitution jw==s (I was taught Heaviside notation at about age 20 ;-) ...Jim Thompson

```--
| James E.Thompson                                 |    mens     |
• posted

The Laplace transform is a specialization of a more general class of integral transforms all derived from the Fourier transform, though many (like the Mellin transform) don't have much application to engineering.

More generally than that, they're a class of operator on a vector-space of functions.

The Laplace variant is preferred in EE because it can operate on many important functions which don't have a finite limit at infinity, like sin an cos, and has a dual space containing transforms of those functions where you don't have to resort to "distributions" which aren't locally integrable, i.e. delta functions etc.

• posted

I studied math in school, not engineering, sorry... ;-)

• posted

I remember just the parts useful to circuit design and Spice modeling ;-)

Oliver Heaviside is the person who formalized such usage in electrical circuits.

...Jim Thompson

```--
| James E.Thompson                                 |    mens     |
• posted

this is the book that has all the good shit in it:

• posted

My set of RF bibles...

...Jim Thompson

```--
| James E.Thompson                                 |    mens     |
• posted

Reference Data For Radio Engineers is handy. Old copies are cheap.

The Williams and Taylor filter book is fundamental.

```--
John Larkin         Highland Technology, Inc
picosecond timing   precision measurement  ```
• posted

Yes, pretty smart guy to invent the operational calculus. Other mathematicians of the 19th century had similar ideas, but AFAIK never applied them directly to engineering (though the Fourier transform came out of Fourier's research into solving the heat equation on bounded domains.)

It wasn't really until the early 20th century that the theory of integral transforms became formalized.

• posted

[snip]

I bought my copy in 1958

My favorite filter book...

"Synthesis of Filters" Jose Luis Herrero & Gideon Willoner

Library of Congress Number: 66-27547

(Peruse the old/used bookstores...

Math intensive, transforms required, not for those who can't already do a hand-math filter design with Laplace (and need to fall back on FilterPro :-)

But excellent for handling depth of stop bands, etc. ...Jim Thompson

```--
| James E.Thompson                                 |    mens     |
• posted

FilterPro is great. As are the tables in Williams. Either one lets me design a filter in 10 minutes and get on with life.

We have the NuHertz software too. It designs amazing LC filters, using standard component values. I can't imagine how it does that. Trial and test? FilterPro handles standard R/C values, too.

Lots of filters deserve to be Spiced, to account for opamp gbw and slew rates and such.

```--
John Larkin         Highland Technology, Inc
picosecond timing   precision measurement  ```
• posted

Lots of possible algorithms that are essentially "trial and test", but significantly more refined than just a random search of the state-space.