T-Pad Impedance Calculator

T-pad impedance calculator can be used to match a load impedance to the source or internal impedance of a driving source.

T-Pad Impedance Calculator

• L-pad Calculator
• Pi-pad Calculator
• T-pad Calculator

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This T-pad Impedance Calculator is an interactive online tool designed to calculate the component values required to match two unequal impedances and will give you the circuit topology as well as the component values.

One of the fundamental theorems of electrical engineering is that maximum power is delivered from a source to a load only when the load impedance equals the source’s internal impedance, and any circuit or device that delivers electrical power to another can be considered to be a source.

That is, for maximum power transfer, the impedance of a load device must equal that of the source. For example, maximum power is transmitted in an audio system when the loudspeaker impedance matches the output impedance of the power amplifier (the source).

However, perfectly matched circuits are not always obtainable in practice so we need to use some form of impedance matching network between the source and load. One such circuit is called a T-pad impedance matching network.

Generally, an attenuating pad consists of a combination of resistors, capacitors and inductors calculated and arranged that the pad network, when inserted between a source and a load, presents the required amounts of impedance matching.

Impedance matching pads are commonly named after the letters their arrangements resemble, so the T-type pad is so arranged that it resemble the capital letter “T” when drawn as a schematic circuit as shown.

T-pad Impedance Matching Configuration

The T-pad circuit can be used between circuits of equal impedances to provide an impedance match in both directions. Also note that the T-pad impedance circuit is unbalanced but is symmetrical when the source/load impedances are equal, and asymmetrical when the source/load impedances are unequal.

T-match Impedance Calculator

Impedance Matching Calculator

Using this Calculator

This “T”, Tee-circuit topology can change depending on the inputs. For example in some topologies there may be two inductors and one capacitor forming an L-C-L type T-network. While in a different configuration it may be two capacitors and one inductor forming an C-L-C type T-network. There is one menu item to select if there is to be any DC current or not, that also affects the topology. The inputs ask for source resistance and source reactance.

The outputs of this tool give you the component values as well as a graph of the impedance looking into the circuit from the source. This allows you to double check the calculator and make sure that it selected appropriate values, by making sure the impedance correctly matches the input impedance. Also remember that the circuit input reactance will be opposite in polarity with the source reactance when matching.

T-pad Impedance Calculator Summary

In this online T-pad impedance calculator tutorial we have seen that the T-pad impedance network is a symmetrical network that can be used inbetween circuits that have equal or unequal impedances, and being symmetrical in its design, can be connected in either direction making it a bi-directional circuit.