Introduction
The operational amplifier is an integrated circuit that has two input pins and one output pin. It is used to amplify and output the voltage difference between the two input pins. Based on its characteristics, operational amplifier has different functions in different circuits. Here introduces common and fundamental op amp circuits examples with descriptions.
A Basic Introduction to Op Amp Circuits
Catalog
Op Amp Diagram and Circuit Analysis
How do you build an op amp circuit? This part introduces the most basic operational amplifier circuits. Understand the role of op amp in different circuits, and do reference design for your own amplifier circuit through the description of the op amp equations. What’s more, you can handle the most common op amp applications through these circuits.
1.1 What is the Inverting & Non-inverting Amplifier?
Figure 1. Inverting Amplifier
In an inverting amplifier circuit, the operational amplifier inverting input receives feedback from the output of the amplifier. Assuming the op-amp is ideal and applying the concept of virtual short at the input terminals of op-amp, the voltage at the inverting terminal is equal to non-inverting terminal.
Figure 2. Inverting Amplifier with High Input Impedance
In electronics, high impedance means that a point in a circuit (a node) allows a relatively small amount of current through. For an inverting amplifier, the input impedance is approximately equal to the input resistance. This is because the input resistor is connected to “virtual ground” in the inverting configuration.
Another Example:
Figure 3. Fast Inverting Amplifier with High Input Impedance
Figure 4. Non-inverting Amplifier
A non-inverting amplifier is an op-amp circuit configuration which produces an amplified output signal. This output signal of non-inverting op amp is in-phase with the input signal applied. In other words a non-inverting amplifier behaves like a voltage follower circuit.
Another Example:
Figure 5. Non-inverting AC Amplifier
Recommended Readings:
Inverting and Non-inverting Amplifier and Their Basics......(1)
Op Amp High Input Impedance and Low Output Impedance......(2)
1.2 Differential Amplifier
Figure 6.
The differential amplifier circuit is a very useful op-amp circuit and by adding more resistors in parallel with the input resistors. It usually has two outputs and two inputs, which is a special purpose amplifier designed to measure differential signals, otherwise known as a subtractor.
1.3 Summing Amplifier
The Summing Amplifier is another type of operational amplifier circuit configuration that is used to combine the voltages present on two or more inputs into a single output voltage.
Example Explained:
Figure 7. Fast Summing Amplifier with Low Input Current
Figure 8. Inverting Summing Amplifier
The inverting summing amplifier is another type of operational amplifier circuit configuration that is used to combine the voltages present on two or more inputs into a single output voltage. When the summing point is connected to the inverting input of the op-amp the circuit will produce the negative sum of any number of input voltages.
Figure 9. Non-inverting Summing Amplifier
The non-inverting summing amplifier is a similar configuration to the inverting summing amplifier. In other words, it is based around the configuration of a non-inverting operational amplifier circuit in that the input (either ac or dc) is applied to the non-inverting (+) terminal, while the required negative feedback and gain is achieved by feeding back some portion.
1.4 Practical Differentiator
Figure 11.
A practical differentiator amplifier is basically a high pass filter and are used in wave shaping circuits, frequency modulators etc. Because differentiators have frequency limitations while operating on sine wave inputs; the circuit attenuates all low frequency signal components and allows only high frequency components at the output. In other words, the circuit behaves like a high-pass filter.
1.5 Op-amp Integrator
An op-amp integrator is an electronic integration circuit that performs the mathematical operation of Integration, that is we can cause the output to respond to changes in the input voltage over time as the op-amp integrator produces an output voltage which is proportional to the integral.
Figure 12. Fast Integrator
Figure 13. Fast Integrator with Low Input Current
Figure 14. Low Drift Intergrator
In Low Drift Intergrator circuit, the output of an operational amplifier always contains signals that could not have been predicted, even with knowledge of the input and an accurately.
1.6 Converter, Detector, Bias Current Compensation, Voltage Comparator
Figure 15. Current to Volatge Converter
A current to voltage converter will produce a voltage proportional to the applied input current. This circuit is required if your measuring instrument is capable only of measuring voltages and you need to measure the current output.
Figure 16. Precision AC to DC Converter
A simple full wave precision rectifier using a single supply operational amplifier in saturation mode, which is to insure precision half wave rectification and unidirectional current flow.
Figure 17. Temperature Compensated Logarithmic Converter
A temperature compensated logarithmic amplifier for signal strength indicator or automatic gain control applications is presented.
Figure 18. Double-Ended Limit Detector
The circuit in see a differential Input to single ended output amplifier will convert a differential (double ended) signal.
Figure 19. Fast Zero Crossing Detector
A zero-crossing detector whose input is a sign wave has been converted into a train of positive pulses at interval T by adding a RC network and a clipping. It can be used to detect phase anomalies, or even as a 'loss of AC' detector, purposes of synchronization, fast and accurate frequency.
Figure 20. Low Drift Peak Detector
Op-amp based peak detector circuit is the modification of basic peak detector circuit, used to remove the voltage drop across the diode. It stores the peak value of input voltages for infinite time duration until it comes to reset condition.
Figure 21. Op Amp Integrator with Bias Current Compensation
The operational amplifier integrator is an electronic integration circuit, where the resistor producing a compensating current flow through the series capacitor to maintain the virtual ground.
Figure 22. Voltage Comparator for Driving DTL or TTL Integrated Circuit
High frequency performance at any gain as a comparator the output can be drived DTL or TTL integrated circuit.
Figure 23. Threshed Detector for Photodiodes
Use operational amplifiers or op-amps to convert the photodiode current to a measurable voltage.
1.7 Offset Voltage Adjustment
The input offset voltage is defined as the voltage that must be applied between the two input terminals of the op amp to obtain zero volts at the output. Ideally the output of the op amp should be at zero volts when the inputs are grounded. The presence of offset can be encapsulated by assuming that the real Op Amp input/output transfer characteristic is y = A (V + – V – + e ) where e is the error in the differential input to the ideal Op Amp.
Figure 24. Offset Voltage Adjustment for Inverting Amplifiers Using Any Type of Feedback Element
Figure 25. Offset Voltage Adjustment for Non-inverting Amplifiers Using Any Type of Feedback Element
Figure 26. Offset Voltage Adjustment for Voltage Followers
Figure 27. Offset Voltage Adjustment for Differential Amplifiers
Figure 28. Offset Voltage Adjustment for Inverting Amplifiers Using 10kΩ Source Resistance or Less
1.8 Sine Wave Generator
Sine Wave Generator Using Op Amp
The Sine Wave Generator is a type of electronic equipment that generates an oscillating frequency in a sinusoidal pattern. One of the popular methods of generating a sine wave with an operational amplifier is to use the Wien bridge configuration.
Figure 29. Low Frequency Sine Wave Generator with Quadrature Output
Figure 30. High Frequency Sine Wave Generator with Quadrature Output
1.9 Op-Amp Voltage Reference
A voltage reference, or a VREF, is a precision device designed to maintain an accurate, low noise, constant output voltage. Ideally, the output should remain constant even as parameters, such as ambient temperature, supply voltage, or the load current change.
Figure 31. Positive Voltage Reference
In a positive voltage reference a non-inverting op-amp buffer is often included to scale the output voltage and supply any current needed.
Figure 32. Negative Voltage Reference
A common way to generate a negative voltage has been to use an operational amplifier (op amp) to invert the output of a positive precision voltage reference. This approach typically requires a positive reference, the op amp, and two supply rails to generate the negative output.
1.10 Instrumentation Amplifier
Instrumentation amplifier is a kind of differential amplifier with additional input buffer stages. It is a differential op-amp circuit providing high input impedance with ease of gain adjustment. Basically, a typical Instrumentation Amplifier configuration consists of three Op-amps and several resistors.
Figure 33. Differential-input Instrumentation Amplifier
Figure 34. Variable Gain, Differential-input Instrumentation Amplifier
Figure 35. Instrumentation Amplifier with ±100V Common Mode Range
Figure 36. Instrumentation Amplifier with ±10V Common Mode Range
Figure 37. High Input Impedance Instrumentation Amplifier
1.11 Precision Current Sink & Source
Op Amp can source or sink current.
Sourcing current means that current is flowing out of the op-amp into the load. Sinking current means that current is flowing in to the op-amp.
Figure 38. Precision Current Sink
For a current sink circuit, opamp are designed to be used in both positive and negative voltages. The op-amp connection is changed, that is the negative input is connected to a shunt resistor.
Figure 39. Precision Current Source
Precision current sources have traditionally been built using op amps, resistors, and other discrete components—with limitations due to size, accuracy.
Figure 40. Bilateral Current Source
1.12 Precision Diode & Clamp
Figure 41. Precision Diode
In this circuit , the op-amp circuit is required to work as an ideal diode. That is, an ideal op-amp wants to make its two inputs equal in voltage through the negative feedback path.
Figure 42. Precision Clamp
Precision Op-Amp Clamp Circuit is the same circuit as the classic simple precision rectifier (set to pass the negative half-sine), but with the non-inverting input of the op-amp.
1.13 Notch Filter Amplifier
Notch filter is a useful circuit to suppress middle- and high-frequency resonance to improve control precision. It work on only a narrow band of frequencies. To be useful, the notch filter must be tuned to the frequency of resonance or of noise generation.
Figure 43. Adjustable Q Notch Filter
Figure 44. Easily Tuned Notch Filter
1.14 Capacitance Multiplier
Capacitance Multiplier uses an op-amp and a small capacitor to simulate a much larger capacitor instead of a transistor.
Example Explained:
Figure 45. Negative Capacitance Multiplier
Figure 46. Variable Capacitance Multiplier
Figure 47. Analog Multiplier
In electronics, an analog multiplier is a device which takes two analog signals and produces an output which is their product. Analog multipliers take two or more analog signals and produce an output which is their product or the sum of multiple products.
2 Other Op-amp Circuit Design
Figure 48. Free-Running Multivibrator
The Op-amp Multivibrator is an astable oscillator circuit that generates a rectangular output waveform using an RC timing network connected to the inverting end. An astable multivibrator uses an op-amp. It generates square waves of its own i.e. without any external excitation.
Figure 49. Op Amp Function Generator
Function generator system can be readily synthesized using operational amplifiers on an approach which uses full when the need for a special need.
Figure 50. Pulse-width Modulator (PWM)
Pulse-width Modulator is a way to control analog devices with a digital output. It uses digital signals to control power applications, as well as being fairly easy to convert back to analog with a minimum of signal. High-frequency op amps can be used for a high-frequency PWM, because op amps are used for the modulator.
Bridge Amplifier
The bridge amplifier is to generate both an inverted and a noninverted output signal. When the amplifier is switched into bridge-mode operation, the signal at the output of the first stage of amplification of channel A is attenuated. In addition, bridging an amplifier refers to the process of combining two of four channels into one or two channels with half the ohms.
Figure 51. Bridge Amplifier with Low Noise Compensation
Figure 52. Wien Bridge Sine Wave Oscillator
A Wien bridge oscillator is a simple circuit that can be set to continuous oscillation, which outputs a sine wave. It acts as a useful reference oscillator for analog circuits, and the output signal can then be manipulated with other analog circuits. It is an excellent circuit for generating a sine wave signal at audio frequencies.
Figure 53. Low Power Supply for Intergrated Circuit Testing
Op-amp IC Testing Circuit basically has voltage comparator inside, which has two inputs, one is inverting input and second is non-inverting input. In normal, putting a good op-amp into the circuit, and they will generate a low frequency in the square wave.
Figure 54. Fast Half Wave Rectifier
Precision half-wave rectifiers are commonly used with other op amp circuits such as a peak-detector or bandwidth limited non-inverting amplifier to produce a DC output voltage. For the positive half cycle of the sinusoidal input, the output of the op-amp will be negative.
Figure 55. Absolute Value Amplifier with Polarity Detector
Absolute Value Amplifier with Polarity Detector Circuit breaks an input voltage signal down into its components. It will handle direct input voltages as well as alternating voltages up to several kHz.
Figure 56. Sample and Hold Circuit Using Op Amp
In electronics, a sample and hold (also known as sample and follow) circuit is an analog device that samples (captures, takes) the voltage of a continuously varying analog signal and holds (locks, freezes) its value at a constant level for a specified minimum period of time. It consists of switching devices, capacitor and an operational amplifier.
Figure 57. Tuned Circuit
A tuned circuit has a very high impedance at its resonant frequency (ideally = infinity). At other frequencies, its impedance is lower. Tuned circuits are used to select or tune in radio stations on a particular frequency and reject all the others. When an amplifier circuit has its load replaced by a tuned circuit, such an amplifier can be called as a tuned amplifier circuit. It is generally referred to as active filters.
Another Example:
Figure 58. Two-Stage Tuned Circuit
Figure 59. Simulated Inductor
A simulated inductor is an active circuit for generating an equivalent inductive reactance, which is implemented with active and passive components. It is used in the design of filters, amplifiers, oscillators and tuned amplifiers.
Figure 60. High Pass Active Filter
A high-pass filter (HPF) is an electronic filter that passes signals with a frequency higher than a certain cutoff frequency and attenuates signals with low frequencies. Active High Pass Filter uses inverting operational amplifier with high voltage gain.
Figure 61. Low Pass Active Filter
A simple active low pass filter is formed by using an op-amp. The operational amplifier will take the high impedance signal as input and gives a low impedance signal as output. The circuit uses an op-amp for amplification and gain control.
Figure 62. Nonlinear OP AMP with Temperature Compensated Breakpoints
As long as the gain of the operational amplifier is large enough, the amplification of the circuit is determined by the external feedback resistance network.
Figure 63. Current Monitor
A current monitor amplifier is a special purpose integrated circuit differential amplifier that is designed to sense the voltage developed across a current shunt and output a voltage proportional to the measured current.
Figure 64. Power Booster Amplifier
A power booster amplifier is typically a hybrid circuit with thick film resistors, ceramic capacitors. A novel power booster amplifier is based on a modified half-bridge topology using separated switches and a floating bridge capacitor.
Figure 65. Long Interval Timer
With the help of high gain high impedance operational amplifier, we can build a long time delay with resistor-capacitor (RC) circuit.
Figure 66. Amplifier for Piezoelectric Transducer
The charge sensitive amplifiers employed for piezo electric sensors cover quite wide range. Piezoelectric transducers used as sensors, typically, the high impedance of the sensor requires an amplifier.
Figure 67. Temperature Probe
An inverting op amp operates with a noise gain of two, which produces twice as much output offset voltage as does a unity-gain buffer. This is a fantastic solution to temperature monitoring.
Figure 68. Photodiode Amplifier
Photodiode amplifier circuit pedance amplifier for amplifying the light- dependent current of a photodiode. The high gain of the op-amp keeps the photodiode current equal to the feedback current. Some are ideally suited for ultra low noise amplification of very small photodiode currents.
Figure 69. High Input Impedance AC Follower
Operational amplifiers have a very high input impedance, which means that they don't suck in much current (ideally, none) at the inputs, typically above 1MΩ as it is equal to that of the operational amplifiers input resistance. Low output impedance and extremely high input impedance make it a simple and effective solution to problematic impedance.
Figure 70. Root Extractor
The proposed extractor is based on the use of two operational amplifiers (op amps) as only active elements.
Figure 71. Basic Log Amplifier
A logarithmic amplifier, or a log amplifier, is an electronic circuit that produces an output that is proportional to the logarithm of the applied input. The simple logarithmic amplifier uses a junction diode as a nonlinear element. In addition, the basic log amplifier can also be constructed by replacing diode by a transistor. The output is proportional to the logarithm of the input given by.
Figure 72. Circuit for Operating the LM101 without a Negative Supply
Figure 73. Circuit for Generating the Second Positive Voltage
Figure 74. Multiple Aperture Window Discriminator
Figure 75. Neutralizing Input Capacitance to Optimize Response Time
Figure 76. Saturating Serve Preamplifier with Rate Feedback
Frequently Asked Questions about Op Amp Circuits
1. What is an op amp circuit?
An operational amplifier is an integrated circuit that can amplify weak electric signals. An operational amplifier has two input pins and one output pin. Its basic role is to amplify and output the voltage difference between the two input pins.
2. Why use an op amp in a circuit?
To convert the current into voltage, a simple circuit with an operational amplifier, a feedback loop through a resistor on the non-inverting, and the diode connected between the two input pins allows you to get an output voltage proportional to current generated by the photodiode, which is evident by the light.
3. How do op amp circuits work?
An operational amplifier, or op amp, generally comprises a differential-input stage with high input impedance, an intermediate-gain stage, and a push-pull output stage with a low output impedance. ... That is, the output gets fed back to the inverting input through some impedance.
4. What are the advantages of op amps circuit?
An op-amp circuit buffers the sensor and allows gain or attenuation circuits to be developed. The output of the sensor is non-linear. An inverting op amp circuit gives you a more linear output than a non-inverting op-amp circuit does.
5. What are the ideal characteristics of op amp?
The so-called ideal op amp is to idealize various technical indicators of op amps, and it must have the following characteristics.
1) Infinite Input Resistance
2) Zero Output Impedance
3) Infinite Open-loop Gain
4) Infinite Common-mode Rejection Ratio
5) Infinite Bandwidth