# opamp help

Discussion in 'General Electronics Chat' started by Xufyan, Sep 10, 2011.

1. ### Xufyan Thread Starter Member

Aug 3, 2010
114
0
is it possible to design an opamp circuit that take the sin of input signal,
ie,

Vo = Sin(Vi) ??

2. ### tgotwalt1158 Member

Feb 28, 2011
111
18
The attached circuit implements the mathematical relationship between the sine and cosine trigonometric functions. Mathematically, if you integrate a sine wave, you get an inverted cosine wave. Basically, it's the same waveform but shifted 90° in phase. Then, if you integrate that cosine wave, you get another 90° phase shift, producing a negative sine wave. Of course, each op amp integrator introduces an inversion as well, so the output of the first integrator is actually a non-inverted cosine wave. This is reversed again by the second integrator, so its output is still a negative sine wave. All we have to do is invert that negative sine wave to get our original sine wave back again. The attached circuit accomplishes this.

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3. ### russ_hensel Distinguished Member

Jan 11, 2009
820
47
more or less right but not an answer to the question.

4. ### russ_hensel Distinguished Member

Jan 11, 2009
820
47
For what range of v in? For what rate of change? You can use sin x aprox x for small x. Then using diodes you can insert some break points to improve the aprox. This approach runs into serious problems for x > pi/2. Try looking up piece wise linear circuits. If this does not work consider a microcontroller.

5. ### JMac3108 Active Member

Aug 16, 2010
349
66
Do you really need a circut that ouptus the sine of an arbitrary input signal? If you have a particular type of input signal in your application, it will be easier to come up wth a circuit to take the sine of it.

6. ### Xufyan Thread Starter Member

Aug 3, 2010
114
0
the AC side is far so easy , integrating a square wave twice gives a sine wave and integrating triangle waves output sine wave but what if i apply Dc voltage at the input side of Opamp ? how it will generate sin output ?
like if the input is 0.5volts the output must be sin(0.5)

is there any way to convert dc voltage to Square wave ? so that i can then convertit into sin wave ??

Last edited: Sep 11, 2011
7. ### tgotwalt1158 Member

Feb 28, 2011
111
18
Here are some Sine Functions and their graphs. If you could produce equivalent op-amp circuit, you will achieve your goal.
See the attached files

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