Operational amplifier circuits problems and solutions

You might want to read the questions at the end of the lab to make sure you have all the information required to answer them before you leave the lab. Note: there is software on the PC's in Singer that communicate with the oscilloscopes so you can get screenshots, or data for plotting in another program e. See me or Ed Jaoudi if you have any questions. In this lab and throughout the rest of the semester you will be using op amps, one of the basic building blocks of analog electronics. For our purposes we will be using an ideal model of the op amp. The circuit symbol for an op amp is shown.

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Content:

• Electronics/Electronics Formulas/Op Amp Configurations
• What is an Operational Amplifier?
• What is the virtual short-circuit (virtual ground) of an op-amp?
• Avoiding Op-Amp Instability Problems In Single-Supply Applications
• Operational Amplifier Question & Answers
• Cascaded Op Amp Circuits
• Learning Electronics
• 6 Misuses of Operational Amplifiers in the Design of Measurement and Control Circuits

WATCH RELATED VIDEO: OP-AMP Circuit : Example 1

Electronics/Electronics Formulas/Op Amp Configurations

An op-amp with no feedback is already a differential amplifier, amplifying the voltage difference between the two inputs. However, its gain cannot be controlled, and it is generally too high to be of any practical use. So far, our application of negative feedback to op-amps has resulting in the practical loss of one of the inputs, the resulting amplifier only good for amplifying a single voltage signal input.

With a little ingenuity, however, we can construct an op-amp circuit maintaining both voltage inputs, yet with a controlled gain set by external resistors. If all the resistor values are equal, this amplifier will have a differential voltage gain of 1. As would stand to reason, V 2 functions as the noninverting input and V 1 functions as the inverting input of the final amplifier circuit. If we wanted to provide a differential gain of anything other than 1, we would have to adjust the resistances in both upper and lower voltage dividers, necessitating multiple resistor changes and balancing between the two dividers for symmetrical operation.

This is not always practical, for obvious reasons. Another limitation of this amplifier design is the fact that its input impedances are rather low compared to that of some other op-amp configurations, most notably the noninverting single-ended input amplifier.

Each input voltage source has to drive current through a resistance, which constitutes far less impedance than the bare input of an op-amp alone. The solution to this problem, fortunately, is quite simple.

Now the V 1 and V 2 input lines are connected straight to the inputs of two voltage-follower op-amps, giving very high impedance. The two op-amps on the left now handle the driving of current through the resistors instead of letting the input voltage sources whatever they may be do it. The increased complexity to our circuit is minimal for a substantial benefit. Differential Op-Amp Circuits An op-amp with no feedback is already a differential amplifier, amplifying the voltage difference between the two inputs.

Therefore: If we wanted to provide a differential gain of anything other than 1, we would have to adjust the resistances in both upper and lower voltage dividers, necessitating multiple resistor changes and balancing between the two dividers for symmetrical operation.

Buffer the Input Voltage Signal Another limitation of this amplifier design is the fact that its input impedances are rather low compared to that of some other op-amp configurations, most notably the noninverting single-ended input amplifier.

What is an Operational Amplifier?

A virtual short-circuit or simply virtual short refers to a condition of a differential input amplifier such as an op-amp in which its noninverting and inverting inputs have almost the same voltage. This condition is called a virtual short-circuit because the differential inputs have the same voltage even though they are not connected together. This condition is met when a negative-feedback circuit is formed using a differential amplifier with a high open-loop gain. When the input terminal on one side is grounded to GND as shown in the figure, it is sometimes called virtual ground.

What is the virtual short-circuit (virtual ground) of an op-amp?

Notes: Determining which "way" the output of an op-amp drives under different input voltage conditions is confusing to many students. Discuss this with them, and ask them to present any principles or analogies they use to remember "which way is which. Notes: It has been my experience that students require much practice with circuit analysis to become proficient. To this end, instructors usually provide their students with lots of practice problems to work through, and provide answers for students to check their work against. While this approach makes students proficient in circuit theory, it fails to fully educate them. Students don't just need mathematical practice. They also need real, hands-on practice building circuits and using test equipment. So, I suggest the following alternative approach: students should build their own "practice problems" with real components, and try to mathematically predict the various voltage and current values. This way, the mathematical theory "comes alive," and students gain practical proficiency they wouldn't gain merely by solving equations.

Avoiding Op-Amp Instability Problems In Single-Supply Applications

Modern operational amplifiers op amps and instrumentation amplifiers in-amps provide great benefits to the designer, compared with assemblies of discrete semiconductors. A great many clever, useful, and tempting circuit applications have been published. This article will discuss a few of the most common application problems and suggest practical solutions. One of the most common application problems encountered is the failure to provide a dc return path for bias current in ac-coupled operational- or instrumentation-amplifier circuits. Depending on the polarity of the input bias current, the capacitor will charge up toward the positive supply voltage or down toward the negative supply.

Operational Amplifier Question & Answers

The ability to diagnose and cure problems in a systematic manner is an exceptionally valuable skill. In PHY students are given a heap of components, a breadboard, and measuring equipment. This virtually guarantees that nothing will work first time, and students are forced to develop troubleshooting skills. Students: please ensure that you can answer 'yes' to the relevant questions below before asking a demonstrator for help. Carry out quick and easy checks first: start with a visual inspection, then use a multimeter, finally an oscilloscope.

Cascaded Op Amp Circuits

Unit Descriptor. This unit covers determining correct operation of basic amplifier circuits. It encompasses working safely, problem solving procedures, including the use of voltage, current and resistance measuring devices, providing solutions derived from measurements and calculations to predictable problems in basic amplifier circuits. Application of the Unit. This competency standard unit is intended for development of competency in either entry-level employment based programs incorporated in approved contracts of training or other approved training programs.

Learning Electronics

Cascaded op amp circuits mean we use multiple op amp connected together head to tail. After learning what is operational amplifier , we will also learn:. As we know, op amp circuits are modules or building blocks for designing complex circuits.

6 Misuses of Operational Amplifiers in the Design of Measurement and Control Circuits

Operational amplifier is a very important component in the measurement and control circuit, and has a very wide range of applications in the measurement and control circuit. As a commonly used device, operational amplifiers are more and more widely used in measurement and control circuits. The measurement and control circuit has more requirements for operational amplifiers than other applications, so more stringent requirements are put forward for the design of operational amplifiers. If the operational amplifier is not properly designed in the actual design process of the measurement and control circuit, it is likely to seriously affect the performance of the entire measurement and control circuit, or even make the circuit unable to work normally.

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In electronics, the open-loop voltage gain of the actual operational amplifier is very large, which can be seen a differential amplifier with infinite open loop gain, infinite input resistance and zero output resistance. In addition, it has positive and negative inputs which allow circuits that use feedback to achieve a wide range of functions. And meanwhile, it can be further simplified into an ideal op amp model, referred to as an ideal op amp also called ideal OPAMP.