Op-amp integrator

Objective

Integrate a ±1 V square wave into a triangle: Vout = −(1/RC)∫Vin dt.

Procedure

1. Run and compare input (square) and output (triangle).
2. Double the frequency: the triangle amplitude halves.

Theory

With R = 10 kΩ and C = 10 nF, 1/RC = 10 000 s⁻¹: during a 0.5 ms half-period a 1 V input ramps the output by 5 V. A 1 MΩ resistor across C limits the DC gain so the output does not drift.

Questions to answer

1. Why is the output inverted?

Components used

2 × Battery / DC source, Ceramic Capacitor 0.1uF (104), Function generator (square), Op-Amp LM741, Oscilloscope (2-channel), 2 × Resistor 220 ohm 1/4W

About the model

Time scale: for the browser simulator the source frequencies are divided by 100 and capacitors / inductors multiplied by 100; the waveforms keep their shape but run 100 times slower. Ideal wires; component models as listed in the catalogue (no parasitics, no temperature drift). Built without a breadboard so the schematic stays readable.

More Analog Circuits Lab experiments

• Op-amp differentiator
• Zero-crossing detector
• Schmitt trigger (hysteresis)
• Common-emitter amplifier
• Emitter follower (common collector)