The article explains how a capacitance multiplier circuit can be built using an operational amplifier configured as a voltage follower and two resistors. An ideal op-amp multiplies the voltage difference between its inverting and non‑inverting inputs by a large factor and outputs the result relative to the supply midpoint. In a voltage follower, the output is connected to the inverting input, causing the output voltage to track the input voltage with sub‑millivolt accuracy.

The capacitance multiplier combines this follower with a capacitor charging through a resistor. Current through the first resistor is (Vsignal – Vcap) divided by its resistance, and current through the second resistor is (Vsignal – Vcap) divided by the second resistor’s value. The total input current equals the sum of the two currents. The ratio of total current to the current through the first resistor is 1 plus the ratio of the first resistor value to the second resistor value, indicating that the capacitor charges more slowly than in a simple RC circuit. This ratio can be interpreted as an effective capacitance that is the product of the actual capacitance and the resistor ratio.

By selecting appropriate resistor values, a 1 µF capacitor can be made to behave as a 1 mF capacitor, increasing the effective capacitance without adding energy storage capability. The technique is useful for signal filtering or timing applications and can employ smaller, lower‑cost components with better specifications than traditional capacitors. However, advances in capacitor technology and the availability of digital timing solutions have reduced the practical advantage of the multiplier in many cases.

The author notes that the circuit is less useful today but remains an illustrative example of op‑amp application. A variant that swaps the capacitor and resistor is suggested for further exploration.