Op-Amp Symbol
Definition: The Op-Amp symbol represents an operational amplifier — a high-gain, differential-input voltage amplifier — defined in IEC 60617-05 and ANSI Y32.2 / IEEE 315 as a triangle pointing to the right with a non-inverting input (In+, marked with '+') at the lower-left, an inverting input (In−, marked with '−') at the upper-left, and an output (Out) at the right apex, used in analogue circuit design for amplification, filtering, integration, and signal conditioning.
Also known as: operational amplifier, op amp, differential amplifier IC, voltage amplifier, linear amplifier.
What the Op-Amp symbol means
The Op-Amp symbol denotes a differential voltage amplifier with very high open-loop gain (typically 100 000 to 10 000 000), very high input impedance (1 MΩ–1 TΩ), and very low output impedance (typically < 100 Ω). The output voltage equals the open-loop gain multiplied by the voltage difference between the non-inverting (In+) and inverting (In−) inputs: Vout = A_ol × (V+ − V−).
In circuit schematics the Op-Amp symbol conveys that the device amplifies the difference between two input voltages and produces a single-ended output. With negative feedback applied from the output to the inverting input, the circuit is stabilised and the gain is set precisely by external resistors or capacitors. Op-amps are the fundamental building block of analogue electronics and appear in virtually every mixed-signal circuit.
How to identify the Op-Amp symbol
The Op-Amp symbol is a right-pointing triangle. The non-inverting input (In+) is marked with a '+' or '⊕' on the lower-left side of the triangle; the inverting input (In−) is marked with a '−' or '⊖' on the upper-left side. The output emerges from the right apex of the triangle. Power supply pins (V+ and V−) may be shown on the top and bottom of the triangle respectively, or omitted for clarity. The triangular shape with the +/− input labels is a unique, universally recognised op-amp identifier.
Function and usage boundary
The Op-Amp amplifies the differential input voltage with very high gain. In open-loop configuration the output saturates at the supply rail for any non-zero input difference. In closed-loop configuration (with negative feedback resistors), the virtual-short principle keeps V+ ≈ V−, setting the circuit gain precisely: for an inverting amplifier, gain = −Rf/Rin; for a non-inverting amplifier, gain = 1 + Rf/Rin. Op-amps implement summers, integrators, differentiators, comparators, active filters, voltage regulators, and many other analogue functions using only external passive components.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60617-05 defines the operational amplifier symbol as a triangle with '+' and '−' input terminals and an output at the apex. Power supply connections are shown as V+ (top) and V− (bottom) or omitted from the diagram for clarity. |
|---|---|
| ANSI/IEEE 315 | ANSI Y32.2-1975 (reaffirmed 1989) and IEEE 315-1975 define the op-amp as the same triangular symbol with '+' (non-inverting) lower-left, '−' (inverting) upper-left, and output at the right apex. This symbol is identical in both IEC and ANSI/IEEE standards. |
| Key difference | IEC 60617-05 and ANSI Y32.2 / IEEE 315 define essentially the same op-amp triangular symbol; the '+'/'-' input label positions may vary slightly (some sources place '+' at the top, some at the bottom), but the convention of '+' = non-inverting and '−' = inverting is universal. |
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Logical terminals
| Logical ID | Editor terminal name |
|---|---|
| in_pos | In+ |
| in_neg | In- |
| out | Out |
Where the Op-Amp symbol is used
- Inverting and non-inverting amplifiers with precision gain set by external resistors for sensor signal conditioning (strain gauge, thermocouple, photodiode)
- Active low-pass, high-pass, band-pass, and notch filters using op-amp integrator circuits for audio processing and anti-aliasing before ADC sampling
- Instrumentation amplifiers (three op-amp topology) for differential measurement of low-level signals in high common-mode environments (medical ECG, industrial bridge sensors)
- Integrator circuits in PID controllers, function generators, and active oscillators (Wien bridge, phase-shift)
- Voltage comparators where the op-amp output saturates HIGH or LOW based on which input is larger, used for threshold detection and zero-crossing detection
- Summing amplifiers that add multiple analogue signals (audio mixer, DAC output combiner) with individual gain coefficients
Key facts
- The Op-Amp symbol is a right-pointing triangle with the non-inverting input (In+, marked '+') at the lower-left, the inverting input (In−, marked '−') at the upper-left, and the output at the right apex; this symbol is defined in both IEC 60617-05 and ANSI Y32.2 / IEEE 315.
- The Op-Amp has three primary pins in schematic representations: In+ (non-inverting input), In− (inverting input), and Out (output); power supply pins V+ and V− are often omitted from the symbol for clarity but must be connected for the device to function.
- The open-loop voltage gain is extremely high (100 000 to 10 million) and in practice the op-amp always operates with negative feedback to set a controlled, stable closed-loop gain.
- With negative feedback, the virtual-short principle applies: the op-amp adjusts its output to keep V+ ≈ V−; for an inverting amplifier, closed-loop gain = −Rf/Rin; for a non-inverting amplifier, gain = 1 + Rf/Rin.
- The gain-bandwidth product (GBW) is constant: for an op-amp with GBW = 1 MHz, a gain of 100 limits bandwidth to 10 kHz; a gain of 10 gives 100 kHz bandwidth.
- Slew rate limits the maximum rate of output voltage change: a 1 V/µs slew rate limits a 10 V peak-to-peak sine wave to 16 kHz before the output waveform distorts.
- IEC 60617-05 and ANSI Y32.2 / IEEE 315 define the same triangular op-amp symbol; the '+' and '−' terminal positions are universal — '+' is the non-inverting (high impedance) input, '−' is the inverting input where feedback is applied.
Diagrams that use this symbol
- phase locked loop block diagram
- op amp 741 pin diagram
- block diagram of digital communication system
- radar block diagram
- data acquisition system block diagram
- 1 to 4 demultiplexer circuit diagram
- fmcw radar block diagram
- block diagram to transfer function
Frequently asked questions
What does the op-amp symbol mean in a circuit diagram?
The Op-Amp symbol represents an operational amplifier — a high-gain differential-input analogue amplifier defined in IEC 60617-05 and ANSI Y32.2 / IEEE 315. The output voltage equals the open-loop gain (typically 100 000–10 million) multiplied by the voltage difference between the non-inverting (In+) and inverting (In−) inputs.
What does the op-amp symbol look like?
The Op-Amp symbol is a right-pointing triangle. The '+' non-inverting input is at the lower-left, the '−' inverting input is at the upper-left, and the output emerges from the right apex. Supply pins V+ and V− may be shown at the top and bottom or omitted. The triangular shape with '+'/'-' labels is unique to op-amp symbols.
What is the difference between the inverting and non-inverting inputs of an op-amp?
The non-inverting input (In+, '+') produces an output voltage in phase with the input: a positive increase at In+ causes the output to rise. The inverting input (In−, '−') produces an inverted output: a positive increase at In− causes the output to fall. In negative-feedback circuits, the feedback resistor connects from the output back to the In− terminal.
What are the pin names of the op-amp symbol?
The op-amp symbol shows three primary pins: In+ (non-inverting input), In− (inverting input), and Out (output). Physical op-amp ICs also have supply pins V+ (positive supply) and V− (negative supply or ground for single-supply types). Power supply pins are typically omitted from the schematic symbol for clarity but are essential for correct operation.
What is virtual short in an op-amp?
In a negative-feedback op-amp circuit, the virtual short (or virtual ground) principle states that the op-amp adjusts its output to keep V+ and V− equal: V+ − V− ≈ 0 V. This occurs because any small difference is amplified by the very high open-loop gain, producing a large output correction that drives the difference to near zero. The inputs are 'virtually short' in voltage but draw negligible current due to the high input impedance.
What standard defines the op-amp symbol?
IEC 60617-05 and ANSI Y32.2 / IEEE 315-1975 both define the operational amplifier symbol as a right-pointing triangle with '+' (non-inverting) and '−' (inverting) inputs. The symbols are essentially identical in both standards.
What is the gain-bandwidth product of an op-amp?
The gain-bandwidth product (GBW or GBWP) of an op-amp is the product of the closed-loop gain and the −3 dB bandwidth. It is approximately constant for a voltage-feedback op-amp: GBW = gain × bandwidth. For a 1 MHz GBW op-amp (LM741, LM358), setting a gain of 100 limits bandwidth to 10 kHz; a gain of 10 gives 100 kHz. Higher-speed op-amps (OPA134, LM6171) have GBW of 8–100 MHz.
Related symbols
- Differential Amplifier symbol
- Op-Amp (DIP) symbol
- Peak Detector symbol
- Precision Rectifier symbol
- Summing Amplifier symbol
- Transimpedance Amplifier symbol
Physical breadboard, PCB, and panel mapping
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