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It is often necessary to know the input impedance of a circuit. For most circuit applications this can be completely ignored. 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. This can be achieved by inserting a high-value resistor, R3 in the diagram, to ground as shown below.

The value of this may typically be k ohms or more. If this resistor is not inserted the output of the operational amplifier will be driven into one of the voltage rails. When inserting a resistor in this manner it should be remembered that the capacitor-resistor combination forms a high-pass filter with a cut-off frequency. The cut-off point occurs at a frequency where the capacitive reactance is equal to the resistance. A non-inverting amplifier using an op amp forms an ideal voltage follower.

The very high gain of the op-amp enables it to present a very high impedance to the signal source whilst being able to accurately follow the voltage waveform. An op amp is configured in its non-inverting amplifier format, linking the output directly to the inverting input and applying the input signal to the non-inverting input.

From the gain equation. Normally op amps are configured to use dual supplies — the chips are intended for use in this way. However, this is not always feasible if only one rail is present. To enable the op amp to run with just one power rail, the positive and negative rails have to be simulated by operating the amplifier half way between the rail and ground, and ensuring the decoupling is sufficient in all the required areas.

This is often referred to as a virtual ground technique. This type of circuit is often very useful when only one supply line is available. Often it is more convenient to adopt this approach that provide an additional supply rail. Skip to content. Dhirendra Yadav. Non-Inverting Amplifier Circuit using an op-amp: Operational amplifiers can be used in two basic configurations to create amplifier circuits. Non-Inverting Amplifier Circuit Basic: The basic non-inverting amplifier circuit using an op-amp is shown below.

Non-Inverting Amplifier Circuit The gain of the non-inverting amplifier circuit for the operational amplifier is easy to determine. AC coupling the non-inverting op-amp circuit: In most cases, it is possible to DC couple the circuit. Basic non-inverting operational amplifier circuit with capacitor coupled input When inserting a resistor in this manner it should be remembered that the capacitor-resistor combination forms a high-pass filter with a cut-off frequency.

Op amp as a voltage follower: A non-inverting amplifier using an op amp forms an ideal voltage follower. Non-inverting amplifier used as a voltage follower Non-inverting amplifier using single supply: Normally op amps are configured to use dual supplies — the chips are intended for use in this way. Typically they are set to provide half the supply voltage and therefore they will be equal in value.

Moreover, for an ideal circuit, R i is supposed to be infinite, as a consequence, no currents can enter the op-amp through any input because of the presence of an open circuit. This observation can also be summarized by saying that the node interconnecting the inverting input and resistances R 1 and R 2 is a virtual short.

For this same reason, all the feedback current across R 1 I is also found across R 2. According to the voltage divider formula, we can express the inverting voltage V — as a function of the output voltage and the resistances:. We can note that the ideal gain presented in Equation 2 is strictly positive and higher than 1, meaning that the output signal is amplified and in phase with the input signal. Instead, the input impedance has a high but finite value , the output impedance has a low but non-zero value.

The non-inverting configuration still remains the same as the one presented in Figure 1. Note that Ri and Ro can be described to be respectively the input and output impedances of the op-amp without any feedback loop open-loop configuration. Finally, the closed-loop gain A CL for a real non-inverting configuration is given by Equation 4 :.

For a real configuration, the gain not only depends on the resistor values but also on the open-loop gain. As a consequence, Equation 4 is simplified back to Equation 2. Even if for real op-amps, a small leaking current enters the inverting input, it is several orders of magnitude smaller than the feedback current. 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.

A inverting amplifier provides the same function as the common emitter and common-source amplifiers. The schematic diagram for an inverting amplifier is shown. This circuit is called a voltage follower or unity gain amplifier. This is used to isolate two cascaded circuits, because of its infinitely. An op amp is a three-terminal device, one called the inverting terminal, The equivalent circuit of the op amp is given below.