Editor's Note: This blog was originally published in December 2019 but has been updated for accuracy.
Operational amplifiers, or “op-amps,” are commonly used in analog electronic circuit development. Engineers of all skill levels frequently incorporate these workhorse components into their electronic designs.
Karl D. Swartzel Jr. of Bell Labs filed a patent for the “summing amplifier” in 1941. Initially, the device was used to perform mathematical operations on analog computers. Thus, the component earned the “operational” part of its name.
Op-amps are the building blocks of many modern analog electronic circuits today. The devices still perform complex mathematical operations like integration and differentiation. However, these versatile components are used in myriad consumer, industrial, and scientific applications thanks to their low cost, optimal performance, and widespread availability.
For example, op-amps are used in audio amplifiers, video applications, medical sensor interfaces, voltage regulators, baseband receivers, analog to digital converters, and so much more.
An op-amp is a high-gain voltage amplifier with differential inputs. Commonly found in integrated circuits (ICs), their input and output terminals produce larger voltage signals than passed through them. The op-amp helps boost signals that typically decrease as they pass through discrete elements in an analog circuit. Ultimately, the devices produce a useful output signal.
An op-amp’s extremely high gain can’t be changed but applying feedback loops to one can control it. Ultimately, adding resistors, capacitors, and inductors creates different configurations on an op-amp circuit produce widely different results.
Overall, the adaptability and versatility of this three-terminal device make it a popular component in many designs.
Selecting the Proper Op-Amp
An ideal op-amp would have infinite open-loop gain, infinite input impedance, zero output impedance, and infinite frequency response with zero noise and no distortion. Realistically, no op-amp can satisfy all these requirements.
General-purpose op-amps will work well in many circuits. However, some applications may require higher performance from a specialty device.
To meet the varying design requirements of different applications, engineers should consider several factors to ensure they select the proper op-amp. These key attributes are detailed below.
One of the most distinctive characteristics of an op-amp is its high gain.
Gain measures an op-amp’s amplification factor —or how much larger the magnitude of its output is compared to its input. It’s typically called an “open-loop gain” or a “large signal voltage gain.”
An open-loop gain measures the device’s gain without positive or negative feedback. When listed, the open-loop gain represents the maximum AC gain at very low frequencies. Ideally, op-amp gain should be infinite, but real values usually range from 20,000 to 200,000 ohms.
By comparison, a large signal voltage gain (aka AVD) depicts the ratio of the output change to the input’s differential voltage shift. It is measured at low-frequency DC, and the amplifier produces a large voltage output. It is typically preferential to an open-loop gain, usually as V/mV. Notably, this gain is measured without an output load, which accounts for loading effects.
Number of Channels
The most common number of channels for an op-amp is 1, 2, or 4. However, they can have as many as 8 channels.
Input and Output Impedance
An op-amp's input and output impedance generally show the relationship between voltage and current.
Input impedance shows how much more current will flow as the voltage increases or how much less current flows when the voltage is decreased.
Actual op-amps have very high input impedance (typical values can be hundreds of millions of ohms). A prime advantage of high input impedance is that minimal current is needed from the source to produce voltage. Ideally, this value should be infinite.
Output impedance, on the other hand, is ideally zero. However, most IC-based op-amps have output impedance values of less than a hundredth of an ohm.
Bandwidth and Gain-Bandwidth Product
An optimal op-amp would have infinite bandwidth and be able to amplify any frequency signal from DC to the highest AC frequencies. However, bandwidth for actual op-amps can only amplify sound through a specific range of frequencies. Once it exceeds its frequency limit, the device can’t produce sound.
The Gain-Bandwidth Product (GBP) describes the frequency at which the op-amps’ amplifier becomes unity-gain. The factor allows designers to achieve the maximum gain an op-amp can produce for a given frequency.
An op-amp's slew rate is the change in the output voltage caused by a step change on the input. It is measured as the ability of a device to change its output voltage by a certain amount in a given amount of time.
An op-amp should have an infinite slew rate in a perfect world, meaning the output from the amplifier would be a distortion-free amplified copy of the input.
Engineers should also be aware that slew rate change values vary according to the type of op-amp used. In actual designs, the higher the slew rate is, the faster the output can change. So, low-power op-amps might yield a slew rate value of one volt per microsecond, while faster op-amps can provide rates of 1,000v/microsecond.
The perfect operational amplifier would have zero noise. Unfortunately, all op-amps contain several internal noise sources such as current, resistor, and more. They are measured at the output and refer back to the inputs. The Equivalent Input Noise Voltage is the most significant noise type, and it's also bandwidth dependent. Overall, designers should aim for this noise value to be as small as possible.
Maximum Input Offset Voltage
Due to manufacturing imperfections, differential input transistors in actual op-amps may not match precisely. If both op-amp inputs were zero, it would produce zero output. Thus, a small differential input voltage must be applied to force a zero output. It is called input offset voltage and should be a small value.
Maximum Supply Voltage
Overall, engineers should consider these factors and how they impact each application’s specific design requirements when deciding which op-amp to use for a project.
Sourcengine provides a massive global database of over 1 billion unique parts accessible anytime and anywhere to meet project needs. Technical specifications are also available for each item.
Below is a brief description of this year’s ten most popular op-amps.
1. OPA310SIDCKR Texas Instruments
This single, high-output-current operational amplifier offers a minimum supply voltage of 1.5 to 5.5 max. The entire OPA310 family features a fast shutdown response and typical enable time of 0.9-µs which allows for power savings when the application involves duty cycling the amplifier signal chain. The OPA310S, in particular, are single amplifiers with rail-to-rail input and output swing capabilities.
To provide robust ESD performance, the OPA310 has a fail-safe input ESD structure with no diodes connected from inputs to the positive power supply rail. The simplified design features an integrated RFI and EMI rejection filter with a no-phase reversal in input overdrive conditions. As such, the op-amps also deliver superb AC performance with a gain bandwidth of 3 MHz. Designers can achieve improved performance and lower power consumption when utilizing the OPA310.
2. TSB712IYST STMicroelectronics
These 6 MHz bandwidth amplifiers are precision amps with rail-to-rail input and output guaranteed to operate from +2.7 V to +36 V single supply and from ±1.35 V to ±18 V dual supplies for other components in the TSB7 family. These amplifiers offer a large supply voltage span and an excellent input offset voltage of 300 µV maximum at 25 °C, specifically +36 V for the TSB712IYST.
The TSB712IYST can be used in various industrial applications such as filters, power supply and motor control, actuator driving, hall effect sensors, and resistive transducers.
3. MCP6499-E/SL Microchip Technology
This single-supply op-amp can supply voltage as low as 1.8V while only drawing 2 mA/amplifier (typical) of quiescent current. The MCP646/6R/6U/7/9 series all possess a low input bias current and rail-to-rail input and output operation. This op-amp has a gain stability of 30 MHz with an input bias current of 1 pA. The MCP6499 is recommended for automotive applications.
Each op-amp within the MCP649 family is integrated with EMI filtering to mitigate the high-frequency electromagnetic noise. All op-amps, including MCP6499-E/SL, are fully specified over the extended temperature range from -40°C to +125°C.
4. OPA2391YBJR Texas Instruments
A dual, micropower precision op-amp with a DSBGA package, the OPA2391YBJR features a unique combination of high bandwidth (1 MHz) and very-low quiescent current (24 µA). It combines rail-to-rail input and output with an ultra-low input bias current of 10 fA, only 45 µV of offset (maximum), and 1.2 µV/°C of drift over temperature. This helps the op-amp maintain high precision in ratiometric and amperometric sensor front ends, which often have demanding low-power requirements. It is an exceptional op-amp in high-gain, low-power applications.
Specifically, the OPA2391 utilizes proprietary e‑trim™ operational amplifier technology, enabling a unique combination of ultra-low offset and low input offset drift without input switching or auto-zero techniques. This Texas Instrument technology tolerates high-output capacitance to alleviate stability problems that are exceedingly common in low-power amplifiers.
5. TSZ181HYLT STMicroelectronics
The TSZ181H is a single operational amplifier with a very low offset voltage with virtually zero drift versus temperature changes. The TSZ181H operates over an extended range of -40 to +150°C and features an ultra-low input bias current. With an excellent speed and power consumption ratio, the TSZ181HYLT offers a 3 MHz gain bandwidth product while consuming 1 mA at 5 V. It is an ideal op-amp for high-accuracy and high-bandwidth sensor interfaces for automotive applications.
The device is also AEC-Q100 qualified, producing 25 µV max with an offset voltage at 25 °C and 44 µV offset voltage over the full temperature range.
6. LM2902BIPWR Texas Instruments
This quad op-amp offers four independent high-gain frequency-compensated op-amps designed to operate specifically from a single supply over a wide range of voltages. Operating from split supplies is possible when the difference between the two supplies is 3 V to 36 V (for B-version devices), 3 V to 32 V (for V-version devices), or 3 V to 26 V (for all other devices), and VCC is at least 1.5 V more positive than the input common-mode voltage.
As a result of the low supply-current drain being independent of the supply voltage, the applications for LM2902B-Q1include transducer amplifiers, dc amplification blocks, and conventional operational amplifier circuits, which can be easily implemented with single-supply-voltage systems.
7. NCV33204DR2G ON Semiconductor
This quad op-amp provides input capabilities that can be driven as high as 200 V beyond the supply rails without output phase reversal. Outputs can swing within 50mv of each rail with rail-to-rail operation that fully uses the supply voltage range. It is designed to work at very low supply voltages (+/- 0.9 V) yet can operate with a supply of up to +12V and ground.
The NCV33204DR2G can output current boosts to its high output current capability without raising the drain current beyond a minimum. A combination of low noise and distortion with a high slew rate and drive capability makes this an ideal amplifier for audio applications.
8. TLV9361IDBVR Texas Instruments
TLV9361 offers strong DC and AC specifications with rail-to-rail output and EMIRR filtering for automotive needs. It has a low input voltage noise density, low offset, and low offset drift at a 10.6-MHz bandwidth. This single op-amp is AEC-Q100 automotive qualified and cost-optimized.
The TLV9361IDBVR also features high output current of ±60 mA and a high slew rate of 25 V/µs for high-voltage and cost-sensitive applications. It has an HBM ESD classification level of 2A and a CDM ESD classification level of C6 under AEC-Q100.
9. TSV792IYST STMicroelectronics
The TSV792IYST is a dual op-amp with a 50 MHz bandwidth unity-gain-stable amplifier. It has excellent accuracy provided by a maximum input voltage of 200 µV, allows amplifying accurately small-amplitude input signal. The op-amp can operate from 2.2 V to 5.5 V single supply with the capabilities to handle an output capacitor up to 1 nF and is fully specified on a load of 22 pF, therefore allowing easy usage as A/D converters input buffer. The rail-to-rail input stage and the slew rate of 30 V/µs make it ideal for low-side current measurement.
The benefits of the TSV92IYST are that the measurement accuracy is virtually unaffected by noise or input bias current, and its signal conditioning is excellent for high frequencies.
10. OPA817DTKR Texas Instruments
This is an 800-MHz, high-precision unity-gain-stable FET-input operational amplifier for various dynamic applications. Equipped with a low-noise junction field effect transistor (JFET) input stage, the OPA817 features a wide gain bandwidth of 400-MHz and a supply range from 6-V to 12.6-V. The fast slew rate of 1000-V/µs allows a wide large-signal bandwidth and low distortion when used as a high impedance buffer in high-speed digitizers, active probes, and other test and measurement applications.
The op-amp offers a combination of pico-amperes of input bias current and low input voltage noise, which makes the OPA817 ideal for instrumentation in applicants with strict requirements, such as medical and scientific testing. It is also available in an 8-lead WSON package with an exposed thermal pad for heat dissipation.
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