# opamp help

#### Xufyan

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

Vo = Sin(Vi) ??

#### tgotwalt1158

Joined Feb 28, 2011
110
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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#### russ_hensel

Joined Jan 11, 2009
825
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.
more or less right but not an answer to the question.

#### russ_hensel

Joined Jan 11, 2009
825
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.

#### JMac3108

Joined Aug 16, 2010
348
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.

#### Xufyan

Joined Aug 3, 2010
114
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.
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 ??

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#### tgotwalt1158

Joined Feb 28, 2011
110
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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