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 The Projects Forum Working on an electronics project and would like some suggestions, help or critiques? If you would like to comment or assist others with their projects, this is the place to do it.

#11
09-22-2010, 07:11 PM
 Papabravo Senior Member Join Date: Feb 2006 Location: Michigan, USA (GMT-5) Posts: 5,850

You can also use an integrator to convert a sine to a cosine. If you have a choice between an integrator and a differentiator you should always choose the integrator.
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#12
09-24-2010, 05:38 AM
 JoeJester Senior Member Join Date: Apr 2005 Location: Grand Prairie, TX, USA Posts: 2,361

The OPs component's values failed to follow the Application Note.

Consider this simulation using the TLC 2201 and the Application Note:
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 differentiator.PNG (80.8 KB, 15 views) differentiator-1.PNG (12.2 KB, 14 views)
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Last edited by JoeJester; 09-24-2010 at 05:56 AM.
#13
09-24-2010, 10:19 AM
 t06afre Senior Member Join Date: May 2009 Posts: 5,939

Perhaps it would be more easy for you to create a "quadrature oscillator" such an oscillator give out a sine and cosine wave.
#14
09-24-2010, 04:36 PM
 dayalrohan New Member Join Date: May 2009 Posts: 7

Quote:
 Originally Posted by JoeJester The OPs component's values failed to follow the Application Note. Consider this simulation using the TLC 2201 and the Application Note:
Not sure what I did wrong,

R2C1 = designed to give 0 dB gain at fc=10 Hz, hence their values. fh is a order higher. Can you give me your designed values?

Also I get correct results in my simulations as well (I use LTspice).

I was thinking of an integrator, but the output will have a DC bias equal to the supply voltage, getting rid of that bias is going to be difficult at such a low frequency. I can use a RC type load I guess to chop off that DC and get that AC on the R load.

I am inclining towards a quadrature type oscillator myself; havent made one ever, does the signal come out nice practically ( I mean distortion free).

Also
@tom66
Removing the compensating components (non-essential), I just increase the noise in the output but the distortion remains.
#15
09-24-2010, 06:42 PM
 JoeJester Senior Member Join Date: Apr 2005 Location: Grand Prairie, TX, USA Posts: 2,361

Quote:
 R2C1 = designed to give 0 dB gain at fc=10 Hz,
According to the application note ... fc = 10f and fh = 100f (both formulas) f (10 Hz) will be -20 dB.
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#16
09-25-2010, 09:45 AM
 DickCappels Senior Member Join Date: Aug 2008 Location: Thailand Posts: 866

From the distortion, it looks like the output of the opamp is capacitively coupled to the non-inverting input, causing hysteresis. Try grounding the noninverting input instead of returning it to ground through a resistor, and that would solve the problem if its coupling via stray capacitance. I think you can get away with leaving R3 out of the circuit because the input bias currents on the inputs of the TLC2201IP are very low.

Other than the stray C, the circuit as you show it is fine.

Last edited by DickCappels; 09-25-2010 at 09:46 AM. Reason: added a phrase
#17
09-28-2010, 02:20 AM
 dayalrohan New Member Join Date: May 2009 Posts: 7

Quote:
 Originally Posted by DickCappels From the distortion, it looks like the output of the opamp is capacitively coupled to the non-inverting input, causing hysteresis. Try grounding the noninverting input instead of returning it to ground through a resistor, and that would solve the problem if its coupling via stray capacitance. I think you can get away with leaving R3 out of the circuit because the input bias currents on the inputs of the TLC2201IP are very low. Other than the stray C, the circuit as you show it is fine.
Well, I tried that as well. As far as I could see, no appreciable change. My simulation runs fine, so it must be something on BB (practical) that is skewing up things. In fact, I coupled a capacitor as high as 100 pF between non-inverting input and output but could not see the same result in simulation.

I tried other options like:

1. Integrator - too much phase delay in my range ( 2-30 Hz)
2. Quadrature oscillator circuit - too much noise, resembles a triangular wave rather than a sine wave.

Any help or any other circuit to convert sine to cos would be really appreciated
#18
09-28-2010, 03:59 AM
 DickCappels Senior Member Join Date: Aug 2008 Location: Thailand Posts: 866

That brings us back to crossover distortion. Is your power supply voltage adequate? Sometimes crossover distortion is helped by a load resistor to ground.
#19
09-28-2010, 02:00 PM
 dayalrohan New Member Join Date: May 2009 Posts: 7

Quote:
 Originally Posted by DickCappels That brings us back to crossover distortion. Is your power supply voltage adequate? Sometimes crossover distortion is helped by a load resistor to ground.
supply is nice, have checked it on oscilloscope for any ac ripple. (I am using +/- 5V)

Even tried a generous offering of bypassing capacitors at the + and - supply near the op-amp.

I thought this was going to be done in 10 minutes, boy was I wrong

 Tags converter, cosine, sine

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