Basically I want a circuit that can convert a sine wave to cosine wave. I cannot use a passive circuit like LR circuit since my frequency of operation is very low ( a few Hz) so the passives would be very huge. What I was trying to do was a op-amp differentiator circuit ; since differentiation of sine is cos. The image of the circuit I am using is attached. http://img683.imageshack.us/i/circuitl.jpg/ My values are R2=157k,R1=1k, C1=.1u, C2=220p : input frequency - 10 Hz However, I am getting a distortion as shown below http://img215.imageshack.us/i/waveforms.jpg/ Any comments/suggestions? If there is any other way of doing this, I am open for it.