What Is an Inverting Amplifier?

What Is a Non-Inverting Amplifier?

Key Differences: Focus on the Essentials

Pros and Cons: Choose What Fits

Performance Battle: Data Tells the Truth

Application First: Which One Is Best for You?

Hands-On: Build and Test Guide

Frequently Asked Questions

Definition

An inverting amplifier is a basic operational amplifier (op-amp) circuit. The input signal goes into the inverting input (negative terminal) of the op-amp. The main feature is that the output signal is opposite in phase to the input. This kind of circuit is useful when phase inversion is needed, such as in sensor signal conditioning.

Working Principle

The input signal goes through an input resistor into the inverting terminal. The op-amp uses its very high open-loop gain, along with a feedback resistor, to force the inverting terminal to act like a virtual ground. The output signal returns to the inverting input through the feedback resistor, creating a deep negative feedback loop. This structure controls the voltage gain and keeps the operation stable.

Circuit Setup

The basic circuit includes an op-amp, input resistor (Rin), and feedback resistor (Rf). The non-inverting terminal is grounded to give a reference voltage. The input signal is applied between Rin and the inverting terminal. Rf connects the output to the inverting terminal. This is a simple setup, ideal for beginners.

Definition

A non-inverting amplifier connects the input signal to the non-inverting input (positive terminal) of the op-amp. The output signal has the same phase as the input. It is a good choice for voltage followers or non-inverting gain circuits, especially in applications like impedance matching to protect weak signal sources.

Working Principle

The input signal directly drives the non-inverting terminal. The feedback path (Rf connects output to the inverting terminal, and the inverting terminal connects to ground through resistor R1) sets a stable operation point and precise gain. The virtual short property makes the inverting terminal follow the voltage at the non-inverting terminal. So, the output follows the input signal closely.

Circuit Setup

The key parts include an op-amp, the input signal connected to the non-inverting terminal, feedback resistor (Rf), and ground resistor (R1). Rf goes from the output to the inverting terminal, and R1 connects the inverting terminal to ground. Unlike the inverting amplifier, the signal source is not grounded, so there’s less load on the input.

Main Features

• High input impedance: The non-inverting terminal has very high input resistance, so it draws almost no current.
• In-phase output: Output matches the phase of the input.
• Low output impedance: Controlled by the op-amp and feedback, which helps drive loads effectively.

Input Impedance Difference

Big difference:

• Inverting amplifier: Input impedance ≈ Rin. If gain is high (small Rin), the input impedance is low. This might load the signal source.
• Non-inverting amplifier: Very high input impedance (hundreds of megaohms), ideal for high-resistance sensors.

Output Characteristics

The output phase follows the gain sign: inverting amplifier gives an inverted output, while the non-inverting amplifier gives an in-phase output. If your application needs strict phase matching, the non-inverting type is better.

Circuit Design Differences

• Input node: In inverting amplifiers, the inverting terminal acts as a virtual ground, good for summing signals. In non-inverting types, the signal goes directly to the op-amp pin.
• Grounding: Inverting amplifiers need a ground reference on the input side, so the signal source cannot float.

Inverting Amplifier Pros and Cons

Non-Inverting Amplifier Pros and Cons

Pros:

• Extremely high input impedance, perfect for weak signal sources
• Output is in phase with input, easy to understand
• Works well as a voltage buffer (when Rf = 0, gain = 1)

Cons:

• Gain must be ≥ 1 (cannot attenuate)
• Needs good CMRR (Common-Mode Rejection Ratio) to reject noise
• High-impedance node is more sensitive to noise

Frequency Response

Both circuits' bandwidth is limited by the gain-bandwidth product (GBW) of the op-amp. Imagine a frequency response graph:

• X-axis: frequency (log scale)
• Y-axis: gain (dB)

Each curve starts with different gain levels and drops at -20 dB/decade. They cross at the GBW point. The inverting type may be more stable at high frequencies due to slightly higher loop gain.

Noise and Distortion

• Input noise: Inverting amplifiers create more thermal noise because of Rin. Comparison charts show non-inverting amplifiers have lower input noise at low frequencies. However, XX Electronics’ low-noise op-amp kits can reduce noise in both types.
• Distortion: Deep negative feedback ensures good linearity. Inverting amplifiers often have lower Total Harmonic Distortion (THD) due to their virtual ground mode.

Linearity

Thanks to negative feedback, both circuits are highly linear in their operating range. The op-amp model and closed-loop gain determine the accuracy. XX Electronics’ high-precision op-amp Δ (±0.001%) greatly improves linearity.

Power and Efficiency

Power usage depends on the op-amp’s static current and resistor values. For low-power design, choose low quiescent current op-amps and avoid very small resistors (which increase current). XX Electronics chips provide full performance with <1mA current.

Best Use for Inverting Amplifier

• Current-to-voltage (Transimpedance) conversion: Converts weak current signals (like from photodiodes) into voltage. Virtual ground helps gather current effectively.
• Signal inversion: Used in audio transmission and some filter designs.
• Summing amplifier: Combines multiple voltage inputs into one (weighted addition) at the virtual ground.

Best Use for Non-Inverting Amplifier

• Voltage buffer (follower): Isolates front and back stages (high input, low output impedance). Ideal for high impedance sensors like piezo ceramics or humidity sensors. Use XX Electronics buffer IC to improve isolation.
• Amplify high-impedance signals: Good for biosignals or piezo microphones.
• Fixed gain (>1) amplification: For sensors with standard output (e.g., bridge sensor differential output to single-ended non-inverting amplifier).

Mixed Selection Strategy

• Source impedance:

High? → Non-inverting

Low? → Either

• Gain requirement:

Need gain <1? → Inverting

• Phase requirement:

Must keep same phase? → Non-inverting

• Circuit complexity:

Need summing? → Inverting

• Noise resistance:

Sensitive to common-mode noise? → Use non-inverting with high CMRR op-amp

Build Steps

1. Choose components: General op-amps (like NE5532/LM358) or XX Electronics precision kits (with matched resistors).
2. Build circuit: Use a breadboard or PCB. Check all connections.
3. Power up: Use ±12V or ±15V dual power supply. Add bypass capacitors.

Test Methods

• Input: Use a signal generator with sine wave (e.g., 1kHz, 100mV).
• Observe: Use dual-channel oscilloscope to view input (CH1) and output (CH2).
• Key measurements:

1. Gain: Vout(p-p) / Vin(p-p) ≈ |Av|
2. Phase: Inverted output flips waveform; non-inverting matches input. Use oscilloscope’s phase tool.
3. DC offset: Use multimeter to check output voltage when input = 0V. Should be near zero.

Troubleshooting

• No output/saturation:

Check if power is on and voltage is correct

Check op-amp pin connections

Measure static voltage at input/output

• Wrong gain:

Check resistor values again

Inspect connection points

• Noise/oscillation:

Add 0.1μF ceramic capacitors near power pins

Keep feedback wires short

Add small capacitor (a few pF to tens of pF) across Rf to compensate

How to identify inverting and noninverting amplifier?

You can differentiate inverting and non-inverting operational amplifier (op-amp) configurations by their phase shift: the output of an inverting amplifier is 180° out of phase with the input, while the output of a non-inverting amplifier is in phase (0° shift) with the input.

What is a inverting amplifier?

The inverting amplifier, a core op-amp circuit, produces an amplified output signal that is phase-shifted by 180° relative to its input signal.

What does an inverting amplifier do?

An inverting amplifier boosts the input signal but reverses its phase (providing a 180° shift). Its functions include changing signal amplitude, setting gain levels, and preparing signals for numerous applications.

What is a non inverting amplifier?

The non-inverting amplifier, a fundamental op-amp circuit, boosts the input signal's amplitude without altering its phase (resulting in 0° phase shift).