Wednesday, 8 June 2016

operational amplifier - Is this correct for non-inverting op-amp?


op-amp sheme



Do 0.1 uf and 100 k ohm act as low-pass filter in here?



Answer




Do 0.1 uf and 100 k ohm act as low-pass filter in here?



No, since there is no current through the parallel RC network, there is zero volts across the network and so


Vout=V=V+=Vin


thus, the circuit implements a unity gain buffer:


Vout=Vin


Another way to see this is to consider the canonical non-inverting configuration in the frequency domain:



enter image description here


The transfer function (frequency response) is:


VoutVin=1+Z2Z1


In the schematic you provide, $Z_1$ is an open circuit, i.e. $Z_1 = \infty $. Thus, the transfer function for your circuit is:


VoutVin=1+Z2=1


which is, as before, just a unity gain buffer. Now, if you place a resistor $R_1$ to ground from the inverting input, the transfer function is:


VoutVin=1+100kΩ||1jω(0.1μF)R1


which will provide some filtering - the details of which I will leave as an exercise for the reader.


:)


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