I'm using this simple circuit to amplify a small signal:
Input voltage is defined by:
Vin = 1.5V + 5mV*sin(wt) with
w = 5 kHz / (2*Pi).
The op-amp I use is the MCP6142 (application requires very low current consumption). I use the second op-amp only to probe the output signal from first op-amp (as scope impedance - 1 MOhm - is much higher than the resistances I use).
The problem I have is that some extra spectral components are added to the output signal:
Here is a capture of the input and output signals over time:
We can see that the input signal - blue - is "pure" as it is generated by the waveform generator of the scope. However the output signal - yellow -, though it is correctly amplified, has some extra spectral components, whose frequencies are multiples of the input frequency. Do you have any idea why this happens?