Op-Amp Calculator

Calculate voltage gain and output voltage for operational amplifier circuits in inverting, non-inverting, and voltage follower configurations.

Operational Amplifier Formulas: Inverting Amplifier: Gain = -Rf / Rin Vout = Vin × (-Rf / Rin) Phase shift: 180° Input impedance: ≈ Rin Non-Inverting Amplifier: Gain = 1 + (Rf / Rin) Vout = Vin × (1 + Rf/Rin) Phase shift: 0° Input impedance: Very high (>1MΩ) Voltage Follower (Buffer): Gain = 1 Vout = Vin Rf = 0 (output to inverting input) Gain in Decibels: Gain (dB) = 20 × log₁₀(|Gain|) Where: • Rf = Feedback resistor • Rin = Input resistor • Vin = Input voltage • Vout = Output voltage
Example 1 (Non-Inverting Amplifier): Rin = 10 kΩ Rf = 90 kΩ Vin = 0.1 V Gain = 1 + (90/10) = 10 Vout = 0.1 × 10 = 1 V Gain (dB) = 20 × log₁₀(10) = 20 dB Example 2 (Inverting Amplifier): Rin = 10 kΩ Rf = 100 kΩ Vin = 0.5 V Gain = -100/10 = -10 Vout = 0.5 × (-10) = -5 V Gain (dB) = 20 dB (magnitude) Phase: 180° inverted Example 3 (Unity Gain Buffer): Configuration: Voltage Follower Vin = 2.5 V Gain = 1 Vout = 2.5 V High input impedance, low output impedance Perfect for impedance matching Example 4 (High Gain Amplifier): Rin = 1 kΩ Rf = 1000 kΩ (1 MΩ) Vin = 0.01 V Gain = 1 + (1000/1) = 1001 Vout = 0.01 × 1001 = 10.01 V Gain (dB) = 60 dB Example 5 (Audio Preamp): Rin = 47 kΩ Rf = 470 kΩ Vin = 0.003 V (3mV microphone) Gain = 1 + (470/47) = 11 Vout = 0.003 × 11 = 0.033 V (33mV) Gain (dB) ≈ 20.8 dB

What is an operational amplifier (op-amp)?

An operational amplifier is a high-gain voltage amplifier with differential inputs and a single output. It's one of the most versatile analog building blocks, used for amplification, filtering, signal conditioning, mathematical operations, and more.

How does an inverting amplifier work?

In an inverting amplifier, the input signal is applied through a resistor to the inverting (-) input, while the non-inverting (+) input is grounded. Gain = -Rf/Rin. The negative sign indicates 180° phase inversion. For example, Rf=100kΩ, Rin=10kΩ gives gain of -10.

How does a non-inverting amplifier work?

In a non-inverting amplifier, the input signal is applied to the non-inverting (+) input. Gain = 1 + Rf/Rin. The output is in phase with the input. For example, Rf=90kΩ, Rin=10kΩ gives gain of 10 (1+9).

What is the difference between inverting and non-inverting configurations?

Inverting: phase inverted, gain = -Rf/Rin, lower input impedance (~Rin). Non-inverting: same phase, gain = 1+Rf/Rin (minimum gain is 1), very high input impedance. Choose based on your application requirements.

What is a voltage follower (buffer)?

A voltage follower is a non-inverting amplifier with gain of 1 (Rf=0, or output directly to inverting input). It provides impedance isolation, converting high-impedance sources to low-impedance outputs without amplification. Essential for driving loads without loading the source.

How do I choose resistor values for op-amps?

Use 1kΩ to 1MΩ range. Lower values (<1kΩ) waste power and stress the op-amp output. Higher values (>1MΩ) are sensitive to noise and input bias currents. Common choices: 10kΩ, 47kΩ, 100kΩ. Use 1% tolerance resistors for precision.

What is input offset voltage?

Input offset voltage is the small DC voltage difference required between inputs to make output zero. Typically 0.1-5mV for general op-amps, <50µV for precision op-amps. It gets amplified by the gain, so high-gain circuits need low-offset op-amps.

What is slew rate and why does it matter?

Slew rate is how fast the output can change, measured in V/µs. For example, 1V/µs can handle ~160kHz for 1V peak signal. Insufficient slew rate causes distortion on fast signals. Choose op-amps with slew rate >10× your signal frequency requirements.

What is gain-bandwidth product (GBW)?

GBW is the frequency where open-loop gain equals 1 (0dB). It determines maximum usable frequency for a given gain. For example, LM358 has 1MHz GBW: at gain of 100, bandwidth is 10kHz. Higher gain = lower bandwidth.

Why is my op-amp oscillating?

Common causes: missing decoupling capacitors (0.1µF near power pins), capacitive load without isolation resistor, excessive gain at high frequencies, poor PCB layout with feedback path coupling. Add compensation capacitors across Rf if needed (1-10pF).

Can op-amps handle negative voltages?

Depends on power supply. Dual-supply op-amps (±5V, ±15V) can handle negative inputs and outputs. Single-supply (rail-to-rail) op-amps work from ground to Vcc. Choose based on your signal range requirements.

What are common op-amp applications?

Amplifiers (audio, instrumentation), filters (low-pass, high-pass, band-pass), integrators, differentiators, comparators, voltage followers, current-to-voltage converters, summing amplifiers, active rectifiers, and oscillators. Op-amps are fundamental to analog signal processing.

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