Method and apparatus for impedance matching in an amplifier using lumped and distributed inductance
View Patent ↗An impedance matching circuit ( 140 ) includes a capacitive element (C 1 , 220 ), having a capacitance C, coupled in parallel with an output node ( 215 ) of the matching circuit, and an inductor (L 1 , 225 ) coupled in series with a transmission line (T 1 , 230 ) between the input node and the output node. The transmission line has a length that, in combination with the inductor, provides impedance substantially equal to the input impedance of the transmission circuit ( 150 ) at a frequency of interest. In one embodiment, the inductor is connected to an output ( 195 ) of an amplifier ( 180 ), and the transmission line is connected to the inductor and to the output ( 215 ). The capacitive element is connected to the transmission line such that the length of the transmission line between the inductor and the capacitive element provides the desired inductance.
1. A method for creating an impedance matching circuit for matching impedances of first and second circuits, the first circuit being a transmission circuit having an input and the second circuit being an amplifier circuit having an output, the method comprising:
determining an input impedance of the transmission circuit at a particular frequency;
determining a capacitance C to be placed in parallel to the transmission circuit; and
determining an overall inductance L of a circuit coupling the first circuit and the second circuit, said determining an overall inductance L including:
determining an inherent inductance of a first line coupling the first circuit to the second circuit;
determining an inductance of a second line coupling the capacitance to the first line; and
determining an inductance to be placed between the first circuit and the second circuit.
2. A method for creating an impedance matching circuit for matching impedances of first and second circuits at a first frequency, the first circuit being a transmission circuit having an input, the method comprising:
selecting a length of transmission line to exhibit a predetermined amount of inductance L 1 ;
selecting an inductor to be placed between the first circuit and the second circuit and having a predetermined inductance L 2 ;
selecting a capacitor to be placed in parallel to the input of the first circuit and having a predetermined capacitance C 2 ; and
determining the impedance of the inductance L 1 , the inductance L 2 , and the capacitance C 2 at the first frequency, wherein the impedance is substantially equal to an input impedance of the transmission circuit at the first frequency.