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If you have a slow op-amp that isn't expected to run at close to that frequency then don't worry about it; you don't need to consider adding a feedback capacitor either but, if you have a fast op-amp and you expect decent flat performance beyond several MHz, then that's the time to worry about calculating the capacitor in parallel with your 91 kohm.

Alternatively you might lower the resistance values by 10 and push the problem away from the low MHz to the tens of MHz at which point your op-amp may have run out of steam. If it hasn't ran out of steam then you might pick a suitable feedback capacitor. Just to add a bit to Andy's answer a mathematical approach.

In order to understand why, you need to be familiar with the frequency response. An opamp has input and stray capacitance on the inputs, which reduces the closed-loop bandwidth, as stated in the answer. Without going into the math, you can find the loop gain which you'd use to find gain and phase margin for stability purposes , and it turns out to be:. That is why, from a math standpoint, you may have to reduce the resistor values to avoid this.

You could go through the math and derive this, I just didn't want to expand a lot more on what already has a good answer by Andy. Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Start collaborating and sharing organizational knowledge.

Create a free Team Why Teams? Learn more. Non-inverting op-amp configuration with capacitor Ask Question. Asked 3 years, 10 months ago. Modified 3 years, 10 months ago. Viewed 6k times. Thanks in advance. Simon Maghiar. Simon Maghiar Simon Maghiar 4 4 silver badges 19 19 bronze badges.

Add a comment. Sorted by: Reset to default. Highest score default Date modified newest first Date created oldest first. Andy aka Andy aka k 23 23 gold badges silver badges bronze badges. And of course low power op-amps tend to be used with high-resistance feedback resistors. Big6 Big6 5, 1 1 gold badge 17 17 silver badges 22 22 bronze badges.

In other words, a non-inverting amplifier behaves like a voltage follower circuit. A non-inverting amplifier also uses a negative feedback connection, but instead of feeding the entire output signal to the input, only a part of the output signal voltage is fed back as input to the inverting input terminal of the op-amp. The high input impedance and low output impedance of the non-inverting amplifier make the circuit ideal for impedance buffering applications. From the circuit, it can be seen that the R 2 R f in the above picture and R 1 R 1 in the above picture act as a potential divider for the output voltage and the voltage across resistor R 1 is applied to the inverting input.

When the non-inverting input is connected to the ground, i. Since the inverting input terminal is at ground level, the junction of the resistors R 1 and R 2 must also be at ground level. This implies that the voltage drop across R 1 will be zero.

As a result, the current flowing through R 1 and R 2 must be zero. Thus, there are zero voltage drops across R 2 , and therefore the output voltage is equal to the input voltage, which is 0V. When a positive-going input signal is applied to the non-inverting input terminal, the output voltage will shift to keep the inverting input terminal equal to that of the input voltage applied.

Hence, there will be a feedback voltage developed across resistor R 1 ,. The closed-loop voltage gain of a non-inverting amplifier is determined by the ratio of the resistors R 1 and R 2 used in the circuit. Practically, non-inverting amplifiers will have a resistor in series with the input voltage source, to keep the input current the same at both input terminals. In a non-inverting amplifier, there exists a virtual short between the two input terminals.

A virtual short is a short circuit for voltage, but an open-circuit for current. The virtual short uses two properties of an ideal op-amp:. Although virtual short is an ideal approximation, it gives accurate values when used with heavy negative feedback. As long as the op-amp is operating in the linear region not saturated, positively or negatively , the open-loop voltage gain approaches infinity and a virtual short exists between two input terminals.

Because of the virtual short, the inverting input voltage follows the non-inverting input voltage. If the non-inverting input voltage increases or decreases, the inverting input voltage immediately increases or decreases to the same value. In other words, the gain of a voltage follower circuit is unity. The output of the op-amp is directly connected to the inverting input terminal, and the input voltage is applied at the non-inverting input terminal.

The voltage follower, like a non-inverting amplifier, has very high input impedance and very low output impedance. The circuit diagram of a voltage follower is shown in the figure below.

The current I 0 across R 0 see Figure 3 can be expressed as a function of the voltage drop across R 0 and the same value of the impedance R 0 :. A simplified version for the expression of Z out is given by the following Equation 6 :. It can be shown that the expression of the input impedance can also be written as a function of the feedback factor:.

The most simple designs for non-inverting configurations are buffers, which have been described in the previous tutorial Op-amp Building Blocks. Its high input impedance and low output impedance are very useful to establish a load match between circuits and make the buffer to act as an ideal voltage source.

We consider a real non-inverting configuration circuit given in Figure 5 :. The resistors, input value, and gain in open-loop are given such as:. First of all, we can compute the value of the closed-loop gain A CL. We can remark that both values are very similar since A OL is high. The currents I R1 across R 1 and I R 2 across R 2 are approximately equal if we consider the leaking current in the inverting input to be much lower than the feedback current.

The design and main properties of this configuration are presented in the first section that presents its ideal model. In the second section, the real non-inverting op-amps are presented. Due to the parasitic phenomena that are intrinsic to their design, their properties change, the expression of the closed-loop gain, input, and output impedances are different. However, the simplified version of these formulas that describe the ideal model can indeed be recovered when we set the open-loop gain to be infinite.

Examples of real configurations are shown in the last section, we present how to calculate the main characteristics of a configuration with the knowledge of the resistors value and input voltage. More tutorials in Operational Amplifiers.

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Disagree Agree. Notify of. The calculation hinges around the fact that the voltage at both inputs is the same. This arises from the fact that the gain of the amplifier is exceedingly high. If the output of the circuit remains within the supply rails of the amplifier, then the output voltage divided by the gain means that there is virtually no difference between the two inputs.

As the input to the op-amp draws no current this means that the current flowing in the resistors R1 and R2 is the same. The voltage at the inverting input is formed from a potential divider consisting of R1 and R2, and as the voltage at both inputs is the same, the voltage at the inverting input must be the same as that at the non-inverting input. Hence the voltage gain of the circuit Av can be taken as:. As an example, an amplifier requiring a gain of eleven could be built by making R2 47 k ohms and R1 4.

For most circuit applications any loading effect of the circuit on previous stages can be completely ignored as it is so high, unless they are exceedingly sensitive. This is a significant difference to the inverting configuration of an operational amplifier circuit which provided only a relatively low impedance dependent upon the value of the input resistor.

In most cases it is possible to DC couple the circuit. Where AC coupling is required it is necessary to ensure that the non-inverting has a DC path to earth for the very small input current that is needed to bias the input devices within the IC. This can be achieved by inserting a high value resistor, R3 in the diagram, to ground as shown below. If this resistor is not inserted the output of the operational amplifier will be driven into one of the voltage rails.

The cut off point occurs at a frequency where the capacitive reactance is equal to the resistance. Similarly the output capacitor should be chosen so that it is able to pass the lowest frequencies needed for the system. In this case the output impedance of the op amp will be low and therefore the largest impedance is likely to be that of the following stage.

Operational amplifier circuits are normally designed to operate from dual supplies, e. This is not always easy to achieve and therefore it is often convenient to use a single ended or single supply version of the electronic circuit design.

An opamp has input and stray capacitance on the inputs, which reduces the closed-loop bandwidth, as stated in the answer. schematic. jellt.xyz › opamp › opamp_3. Electronics Tutorial about the Non-inverting Operational Amplifier or Non-inverting Op-amp which is basically an Op-amp circuit with Positive Feedback.