analog circuit to compute sine of voltage

Isn't that a VCO? XR2206 came to mind... Dunno if that old chip is still around.

D from BC British Columbia Canada.

Oh, and by the way, an input voltage range corresponding to -180 degrees to +180 degrees is sufficient.

Actually, I don't want the circuit itself to be an oscillator, just to produce the sine of a given input voltage. That is, if the input voltage is fixed over time, then so would the output be. I imagine analog computers must have had circuits like this in the old days...

Oh... a phase shifter for sin.

I'm not sure but, isn't that some quirky thing of electronics where the signal is distorted to give the appearance of a different initial phase?

It's phasey but dunno if it's good enough... Patent 3571732

The output is square though. Filter it for sine? The idea here can be IC'ized if crafty at electronics

I suppose a hardcore solution would be using a DDS chip.

Beats me.. just tossing out ideas..

D from BC British Columbia Canada.

Analog Devices used to make a dedicated chip for this, the AD639. It worked pretty well, too. RIP.

Cheers,

Phil Hobbs

Oops .. ignore my 2nd post..

It's typical.. but I'll say microcontroller. Onboard A/D converter >math (or look up table) > DAC Often that's too heavy for most.

As for analog computing with op amps, I'm only familiar with add, subtract, multiply and divide.

Sine series is 3 5 7 sin(x) = x - x + x + x ..... - - - 3! 5! 7!

Ugh.. I wouldn't want to do that with op amps..

D from BC British Columbia Canada.

I found a data sheet at

. That's EXACTLY what I need. Darn, it's discontinued!

In the datasheet there is a patent cited, where you can see the schematic:

If you want to build it for your own usage, you can use this patent without paying for it (at least this is the regulation in Germany). But you may need many parts.

What are your frequency, delay and precision requirements? As D from BC suggested, with a microcontroller it would be easy.

--
Frank Buss, fb@frank-buss.de
http://www.frank-buss.de, http://www.it4-systems.de

dumbfuck. An Analog!!! Got it? Not a digital. He's talking about Opamp/transistor circuit, The answer is Yes, there is a circuit that will do what he wants, it need to be implemented. Why should I tell? this isn't easy, If I am paid, yes I can do it for him.

You can filter my posts if you don't like'm.. :P

D from BC British Columbia Canada.

For sure.. I'd rather learn assembly from scratch than do trig with op amps. :P There's probably a sin math assembly routine downloadable somewhere. If so, I'd say that's 90% of the work done.

This might be an example of how ugly it gets with op amps:

Figure 4 Cube generator. 4 op amps 4 transistors. That helps with the 1st part (X^3/3!) for the series for sin. The other ^/! parts are needed for more accuracy.

D from BC British Columbia Canada.

This means the delay and frequency of the input voltage changes are low. One idea would be to build a sine oscillator and a sample-and-hold circuit, which samples the sine output after some time n, starting from zero crossing from low to high, where n is proportional to the input voltage. I don't know how to build this, but should be straight forward to design for an analog expert, maybe with two quad op-amps.

--
Frank Buss, fb@frank-buss.de
http://www.frank-buss.de, http://www.it4-systems.de

See figure 8 on p.7:

-- Joe

It's possible to do a few terms of the Taylor series with multipliers and such like, but I agree that digitally makes the most sense unless there are some really weird constraints.

There was once a demand for that sort of thing.. hence this (obsolete) chip from AD:

Best regards, Spehro Pefhany

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"it\'s the network..."                          "The Journey is the reward"
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Embedded software/hardware/analog  Info for designers:  http://www.speff.com

I should have scrolled down first..

Best regards, Spehro Pefhany

--
"it\'s the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

Depending on the accuracy and the stability required, you can make a piecewise approximation of sin in the range of +/- Pi/2 using an opamp with the diodes in the feedback path or something like that.

The more accurate solution would be the following:

1. Generate a frequency
2. Divide it by triggers to get the phases 0, 90, 180, 270.
3. Pass the phases through the VCAs controlled by the input voltage. Then add them together. So the resultant phase would be controlled by the input.
4. Synchronously rectify to get the desired Sin(x) output.

And, of course, you can make Sin(x) by a microcontroller.

Vladimir Vassilevsky DSP and Mixed Signal Consultant

This sounds very interesting, especially so because you exhibit the fortitude ( or maybe the cluelessness, dunno ) to attempt a purely analog solution. There may be some confusion on dependent system variables here though. By driving a motor in simulation of a pendulum, you are really talking about the angular displacement of the motor shaft, for which measurement you have a shaft encoder, and this is the output you want to control. The angular displacement is the double integral of the torque which in turn is proportional to the motor current drive. This arrangement then naturally lends itself to what is called an implicit analog circuit representation of the second order differential equation of angular displacement variation in time, but there are some details to work out to simulate a lossless self-sustaining oscillatory system, and I suspect you may be talking about large displacements for which the equation is nonlinear.

Yep. I used that part some 30 years ago to make a function generator for GenRad's portable testers.

I still have that schematic somewhere here. If anyone wants to see it, let me know, and I'll scan it into a PDF... it's only on paper right now.

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Sure, I like collecting schematics of antique solid state electronics...

If you don't mind the function having knees in it, you can do a fairly good job with a couple of packages quad of rail to rail op-amps. Each op-amp amplifies the input voltage with a different gain. The outputs of the op-amps are summed together with resistors.

Near zero volts all of the op-amps are providing gain so the slope of F(X) is large. As you move away from zero, the op-amps start hitting the rails (each in turn) and reducing the slope of F(X). When the lowest gain op-amp hits the rail, you are at the peak.

With two packages of quad op-amps, you can do a 16 point curve.