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Ping Jim Thompson Sine Shaper question ????

Not necessarily. Some posters (JL on several occasions) have expressed issues with quads where common bias circuitry caused undesirable cross-talk between OpAmps (or comparators) in the same package.

I don't do hardly any designs with jelly-bean parts so I can't say with certainty which parts would have cross-talk issues.

It just struck me that rail-to-rail output devices are unlikely to have the problem.

Singles would work.

An alternate solution is to add 8 more diodes and 8 more resistors... preventing railing. I can post that solution if there is interest... next week sometime... another deadline looms ;-) ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| STV, Queen Creek, AZ 85142    Skype: skypeanalog |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 

             I'm looking for work... see my website. 

Thinking outside the box...producing elegant & economic solutions.
Reply to
Jim Thompson
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ah, got ya :)

Zeners would do it, is that what you mean?

NT

Reply to
tabbypurr

No. A "catcher" loop that stops the OpAmp back-swing when it isn't in "clamp" mode. ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| STV, Queen Creek, AZ 85142    Skype: skypeanalog |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 

             I'm looking for work... see my website. 

Thinking outside the box...producing elegant & economic solutions.
Reply to
Jim Thompson

I'm not imagining it. Maybe show us some time when your deadlines are dead.

NT

Reply to
tabbypurr

Interesting and pretty idea. I wonder how many degrees of freedom you need to allow for the not quite ideal tanh function of real components.

I gave it a try in a spreadsheet and optimising for |x| < pi/2 got a surprisingly good fit to a sine wave using least squares.

pseudosine(x) = (tanh(ax)-bx)*c

where a = 0.3374, b = 0.2708, c = 9.386

A slightly lucky solution got an even better fit requiring the residuals to be multiplied by 1000 to be viisible on the same graph. Leading error term is about 0.02% of third harmonic judging by eye.

a = 0.3813, b = 0.27166, c = 9.125

Insisting on having absolutely no discontinuity in gradient at the peak ties down the solution but might not be minimum THD.

I can't quite reproduce your results exactly but the conclusion is that it ought to work rather well with a bit of fine tuning. It is a bit tetchy about the parameter tuning > 3 sig fig needed ideally.

--
Regards, 
Martin Brown
Reply to
Martin Brown

Quicky...

In the sine shaper case this "R" will affect the sizing of the PWL step resistors. ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| STV, Queen Creek, AZ 85142    Skype: skypeanalog |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 

             I'm looking for work... see my website. 

Thinking outside the box...producing elegant & economic solutions.
Reply to
Jim Thompson

Right, cheers. Not come across that one. My remaining braincell was trying to think in terms of adding feedback when output got within a diode drop of a rail.

NT

Reply to
tabbypurr

Oh, I like it. Thanks.

George H. (A thread on simple (1) opamp circuits would be fun for me... right, I'll start on when I have more time.)

Reply to
George Herold

+1

NT

Reply to
tabbypurr

+2 ;-) ...Jim Thompson

-- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at

formatting link
| 1962 |

I'm looking for work... see my website.

Thinking outside the box...producing elegant & economic solutions.

Reply to
Jim Thompson

are you allowed 2 votes? I won't tell though.

NT

Reply to
tabbypurr

Accumulating ;-) ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| STV, Queen Creek, AZ 85142    Skype: skypeanalog |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 

             I'm looking for work... see my website. 

Thinking outside the box...producing elegant & economic solutions.
Reply to
Jim Thompson

Yep, I can see how to do that with a pair of opamps. One monostable to set pulse width, 2nd integrator to add the incoming pulses analoguely.

NT

Reply to
tabbypurr

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