Square root circuit

On Fri, 03 Jul 2015 10:27:51 -0700, John Larkin Gave us:

No, you jacked off at the mouth about his prior reference to security, and I immediately knew it was the water device you referred to.

A new corner you trapped yourself into here.

On Fri, 03 Jul 2015 12:31:58 -0500, John S Gave us:

My brain and memory works. Apparently your does not, as you prefer to jack off at the mouth towards folks you know nothing about.

You know nothing about the group either as JL made no specific reference. He knew that JF would know what he referred to, and some of us who actually read the group's posts remember as well. So, it was obvious to me what device JL mentioned. I guess you have Alzheimer's

You? You're just a childish putz, ala KRW.

Dumb solution (sorry if someone already suggested this)

LTC6992 + SPDT analog switch + LPF

Probably about 7 parts total with no particular tolerances, calibration or worries about temperature. Only question would be the acceptability of the $3.83 LTC6992.

I can see that making a cool square-er, but how does it take the root?

Yeah, has to go in a feedback loop, of course. I *knew* someone sharp (or less dull than I was when I wrote it) would pick it up while I was out.. face-palm.

I like the squaring bit.

There must be a clever simple PWM way to do a square root. Somehow.

Why so many opamps? I was just going to expand on the inverting amp with a ladder of diode and R1

George H.

Why so many opamps? I was just going to expand on the inverting amp with a ladder of diode and R1

George H.

Nice part, thanks. I don't mind the need for a feedback loop. I worry about how it works at zero volts?

George H.

If if you set up a PWM waveform such that the mark-to-period ratio is that of of the square root of your voltage to be squared rooted to a (necessaril y larger) reference voltage, two PWM modulators in succession - the second working on the - filtered - output of the first, the output of the second w ill be the voltage you want squared rooted, and the output of the first wil l be the square root.

It will be slow vis-a-vis the PWM frequency, which could be quite fast.

Be advised that a diode can be used for square law operations. Been around since the '20s methinks.

Instead of LTC6992 you can make usable 0-100% PWM with a much cheaper LM311 (or nowadays more likley MCP6561) and voltage reference of your preference, for maximum cheap-skateness a TL431 :)

piglet

You don't need an opamp at all; just soft clip at a couple of levels with diodes, two or three segments. All you want is a slope change downstream of the PID... 10:1 or so should be enough.

The gain gets infinite. That's always interesting.

If you believe that MOSFETs are squarers, you can just connect G & D and drive the drain with a current. Of course there's a large and poorly controlled offset voltage.

Cheers

Phil Hobbs

Actually it goes to zero. It is sort of large nearby, though. ;)

Cheers

Phil Hobbs

Seems a log amp is we'zz all been talking about? If so does any one use the log104 ic? it was Burr-Brown. I think TI may be a supplier now. Just thought ...

Jamie