Op-Amps: Practical Integrator

An integrator circuit is built as shown in the figure with the 10 Mohm resistor in parallel with the capacitor for leak resistance.

 

The input and output wave forms for 1kHz square wave inputs is graphed using a computer.

 

When the 10Mohm resistor is removed, there is considerably more noise in the wave form. The 10 Mohm resistor effectively reduces the leak resistance of the capacitor. If we assume a leak resistance of 100 Mohm already in the capacitor, as was discussed in the text, then the 10 Mohm parallel resistor creates a equivalent resistance of 9 Mohm.

So much more noise when compared to the other wave forms.