Open-circuit Time Constant Method

The open-circuit time constant method is an approximate analysis technique used in electronic circuit design to determine the corner frequency of complex circuits. It also is known as the zero-value time constant technique. The method provides a quick evaluation, and identifies the largest contributions to time constants as a guide to circuit improvements.

The basis of the method is the approximation that the corner frequency of the amplifier is determined by the term in the denominator of its transfer function that is linear in frequency. This approximation can be extremely inaccurate in some cases where a zero in the numerator is near in frequency.

The method also uses a simplified method for finding the term linear in frequency based upon summing the RC-products for each capacitor in the circuit, where the resistor R for a selected capacitor is the resistance found by inserting a test source at its site and setting all other capacitors to zero. Hence the name zero-value time constant technique.

Read more about Open-circuit Time Constant Method:  Example: Simple RC Network

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