Master the Basics: Amplify Signals

One of the main purposes of using operational amplifiers—op-amps—is to amplify electrical signals. Whether you’re designing audio systems or sensor interfaces, understanding how to build amplifier circuits is a foundational skill. In this guide, we’ll cover two basic op-amp configurations: the inverting amplifier and the non-inverting amplifier.

Inverting Amplifier

The inverting amplifier flips (inverts) and scales the input signal. It uses two resistors:

• R_in: connects the input signal to the inverting (-) terminal of the op-amp
• R_f: connects the output to the inverting (-) terminal (feedback)
• The non-inverting (+) terminal is grounded

Voltage gain formula:

Gain = -R_f / R_in

Example:

If R_f = 10kΩ and R_in = 1kΩ, then the voltage gain is -10. This means the output voltage will be 10 times the input voltage, but inverted.

Why the negative gain?

Op-amps try to make both inputs equal. Since the non-inverting input is grounded (0V), the inverting input will also stay at 0V. A positive input creates current through the resistors, and the op-amp compensates by driving its output in the negative direction to maintain balance.

Inverting Amplifier Demonstration

Built with:

• R_in = 1kΩ
• R_f = 10kΩ
• Input signal: 400mV peak-to-peak sine wave

Result:

The output signal is 10 times larger and inverted. When the input is positive, the output is negative—and vice versa.

Non-Inverting Amplifier

In a non-inverting amplifier, the input signal goes to the non-inverting (+) terminal. A feedback resistor R_f and a resistor R_2 form a voltage divider between the output and ground.

Voltage gain formula:

Gain = 1 + (R_f / R_2)

Note: You can’t build a non-inverting amplifier with a gain less than 1.

Non-Inverting Amplifier Demonstration

Built with:

• R_2 = 1kΩ
• R_f = a 10kΩ potentiometer for variable gain

Results:

• When R_f = 0Ω → Gain ≈ 1 (acts like a voltage follower)
• When R_f = 1kΩ → Gain = 2
• When R_f = 10kΩ → Gain = 11

The output is in phase with the input and scaled based on the resistor values.