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Impedance matching in low pass filter

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expertengr

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Hi,

The low pass filter using op amp in the following link shows gain is 1 (unity gain) but the question is: will it remain 1 for any combination of R and C in the circuit below ?

https://www.electronics-tutorials.ws/filter/filter_5.html


The input impedance of op amp is high, how this should be considered while designing low pass filter using op amp ?

Thanks in advance for your replies
 

will it remain 1 for any combination of R and C in the circuit below ?
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Yes, for reasonable R and C values. Filter R will be choosen several orders of magnitude below OP input resistance.

The input impedance of op amp is high, how this should be considered while designing low pass filter using op amp ?
Click to expand...
The problem has little relation to impedance matching as it's usually understood. Relevant criteria are resistor noise, impedance of the driving source, OP input bias and noise current, susceptibility to crosstalk.
 

    V

    Points: 2
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In earlier years I thought I should try to 'save current' even at levels below 1mA. It was silly of me. One time I built a low frequency oscillator. I tried using a very high R value (several M ohms), and a large capacitor.

Its frequency was way off. I found that the capacitor was leaky. This is just one of those things we don't always anticipate. When we use very high resistor values, it allows circuit operation to be easily affected by unseen invisible loads... inside IC's, meters, oscilloscopes, etc.

This made me realize it's a good idea to reduce resistor values so there is ample current flowing through our circuit.
 

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    Points: 2
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