![]() In general, the complex conjugate of the impedance Z = R + jX is Z* = R – jX, where R is the real part and X is the imaginary part of the complex impedance Z. This means that the impedances of the load and source must be complex conjugate to each other. In addition, it states that each reactive component of the source and the load should be equal in magnitude but opposite in sign. It states that to obtain the maximum external power from a source with a finite internal resistance, the resistance of the load must be equal to the resistance of the source as seen from its output terminals. Impedance matching is based on the maximum power transfer theorem. For example, this means that an inductive component must be capacitively compensated. For matching, the inductive or capacitive component must be compensated with its counterpart – the so-called complex conjugate component. In high-frequency engineering, loads are often complex, i.e., they have an inductive or capacitive component in addition to their resistive component. Therefore, extreme care is taken in the initial design of such a front-end to ensure that each device in the chain is matched to its load. It’s clear that unnecessary losses cannot be tolerated in a circuit that already carries extremely small signal levels. An example of the need for power transfer can be found in the front end of any sensitive receiver. ![]() It’s designed to ensure the maximum possible power transfer between a source and its load and to minimize signal reflections from the load. Theory of complex conjugate impedance matchingĬomplex conjugate impedance matching is a very important technique in RF circuit design. ![]() The design of this circuit is the topic below. It’s complex to calculate the design of the filtering and matching circuit for an NFC application, so several iterations may be necessary due to material tolerances of the components. In contrast to the comparable RFID standards on the same frequency of 13.56 MHz, NFC is better suited for sensitive applications such as data communication and secure financial transactions thanks to its short range of less than 10 cm. NFC enjoys great popularity because it can be used with smartphones. Near-field communication (NFC) is a short-range, high-frequency, low-bandwidth wireless communication technology that enables standardized communication between two mobile devices such as smartphones, smartcards, stickers, or tags. The challenges are the filter and matching network to which the NFC antenna is connected. To enable a device to communicate via near-field communication, you need a microcontroller, an NFC interface, and an antenna. Here's a look at the theory of complex conjugate impedance matching when it comes to NFC.
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