GenxiTechSolutions

How Does a Non-Inverting Amplifier Work?

LTspice schematic of a non-inverting op-amp amplifier with 10k and 20k resistors

A non-inverting amplifier is one of the most common op-amp circuits used to boost a signal's voltage without flipping its polarity — meaning the output waveform stays perfectly in phase with the input. In this article, we'll break down how it works, derive the gain formula, and walk through a real simulation in LTspice where a 5V signal is amplified to 15V.

What Is a Non-Inverting Amplifier?

In a non-inverting amplifier, the input signal is applied directly to the op-amp's non-inverting (+) terminal, while a voltage divider made of two resistors (R1 and R2) feeds a portion of the output back into the inverting (-) terminal. This creates negative feedback, which stabilizes the gain and keeps the output in phase with the input.

LTspice schematic of a non-inverting op-amp amplifier with 10k and 20k resistors
LTspice schematic: non-inverting amplifier with R1 = 10k, R2 = 20k, and a ±18V dual supply.

The Gain Formula

The closed-loop gain of a non-inverting amplifier is given by:

Av = 1 + (R2 / R1)

Where:

  • R2 is the feedback resistor (connected between the output and the inverting input)
  • R1 is the resistor connected between the inverting input and ground

Worked Example: 5V In, 15V Out

Using the LTspice circuit above, R1 = 10kΩ and R2 = 20kΩ. Plugging these into the formula:

Av = 1 + (20k / 10k) = 1 + 2 = 3

The input source is a 5V peak sine wave at 50kHz with no DC offset — SINE(0 5 50k). Since the gain is 3, the output becomes:

Vout = Av × Vin = 3 × 5V = 15V peak

The op-amp is powered from a ±18V dual supply (V3 = +18V, V2 = -18V), which gives enough headroom so the 15V peak output never clips against the rails.

LTspice simulation waveform showing 5V input amplified to 15V output with no DC offset
Simulation result: red trace is the 5V input, blue trace is the amplified 15V output — both centered at 0V with no DC offset.

Why There's No DC Offset

Because R1 connects straight to ground and the input signal itself has zero DC component, there's no DC bias introduced into the circuit. The output waveform is simply the input scaled by the gain and stays centered on 0V, just like the simulation confirms.

Key Takeaways

  • Non-inverting amplifiers keep the output in phase with the input.
  • Gain is always ≥ 1, calculated as 1 + (R2/R1).
  • A dual supply (like ±18V here) allows the output to swing both positive and negative without clipping.
  • With no DC offset at the input and R1 tied to ground, the output stays centered at 0V.

Frequently Asked Questions

An op-amp circuit where the input signal connects to the non-inverting (+) terminal, producing an output that is in phase with the input and amplified by a fixed gain.

Gain (Av) = 1 + (R2/R1), where R2 is the feedback resistor and R1 connects the inverting input to ground.

Because of the "+1" in the formula, a non-inverting amplifier can never have a gain below 1, unlike an inverting amplifier which can attenuate signals.

No, as long as the input has no DC component and R1 is tied to ground, the output stays centered at 0V.

A dual supply gives the output enough voltage headroom to swing both positive and negative without clipping against the power rails.
🤖

GenxiTech Assistant

Online · AI Powered · Always Ready