Weekly PULSE Issue
Kaivan Karimi – Dir. of Global Strategy, Microcontroller Group, at Freescale
L-Match
Impedance Matching Circuit
L Match Impedance Calculator
The L match circuit gets its name because the circuit topology can look like the letter “L”. This tool will help you create a matching circuit so that optimal power transfer occurs between unmatched loads. This technique doesn’t work for wide band requirements, but is a simple way to achieve this at a specific frequency. This calculator will give you the circuit topology as well as the component values.
L Match Circuit Description
There are some important items to understand when using this tool. The circuit topology can change depending on the inputs. In all topologies there is one inductor and one capacitor, but the location of these components changes. 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. If you are unsure what the reactance is set it to zero for a first pass approximation.
The outputs of this tool give you the component values as well as a graph of the impedance looking into the L 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.
L Match Circuit Formulas
For Pass DC Current
Z_{input}=\left ( \left ( R_{L}+jX_{L}+\left ( \frac{1}{j\cdot \omega\cdot C} \right )\right )//\left ( j\omega\cdot L \right ) \right
For Block DC Current
Z_{input}=\left ( \left ( R_{L}+jX_{L}+\left ( j\omega\cdot L \right )\right )// \right )\left ( \frac{1}{j\cdot \omega\cdot C} \right )
