Find Poles and Zeros of a Circuit by Inspection

 Ing. Cristoforo Baldoni

In this article, focused on ‘Poles and Zeros of a Circuit‘, we will explore the technique of identifying the count of poles and zeros within a transfer function, including those in complex linear networks, solely through visual inspection. This method obviates the need for calculating the analytical expression of the transfer function. By the conclusion of this article, you will have the capability to swiftly determine the number of poles upon initial examination.

Once the output is established, this approach also enables you to ascertain the quantity of zeros through inspection and subsequently compute the precise symbolic form of the transfer function. Additionally, you can calculate the exact values of both zeros and poles employing user-friendly software tools readily accessible for free. We will validate the findings using SPICE analysis.

The primary objective of this article is to delve into the concepts of poles and zeros within a transfer function, elucidating their physical significance. Furthermore, we aim to furnish valuable analytical tools to aid analog circuit designers and control systems engineers in their endeavors.

How many POLES does this circuit have?


And how many does this high-pass filter have?


If your response to the initial question is 9 or 8, or if you do not identify a fifth-order filter (with five poles) in the filter’s illustration, then you should proceed to read this article.

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