Practical MMIC Design
Filled with real-world design techniques and rules of thumb, this practical resource offers professionals a unique look into the day-to-day practices of MMIC production and the economics associated with it.
TABLE OF CONTENTS Practical MMIC Design
5.1: Impedance Matching and the Smith Chart
5.1 Impedance Matching and the Smith Chart
Designing circuits involves the efficient transfer of signals; for example, in the case of amplifiers, it involves getting signals into active devices to amplify the signals, then transferring the higher level signals into other circuits, transmission lines, or antennas. In the early days of electric motors, it was found that to get the most efficient transfer of power from the battery (source) into the motor (load) required that the resistance of the different parts of the circuit be the same, in other words, matched; this is known as the maximum power transfer theorem [1]. The transmission lines can be made to be 50 ?, but the active devices are not normally 50 ?, so matching the active devices is one of the first design tasks.
5.1.1 Matching
The impedances of the active devices are seldom purely resistive, so the maximum power transfer must take account of the reactive part of the source and load impedances. In fact, to get maximum power transfer, the load impedance must be the complex conjugate of the source impedance. Conjugate means of equal value and opposite sign, so if the source has impedance Z S = R + jX, then the load must have the impedance Z L= R - jX to be matched. Effectively, this means that the net phase difference is reduced to 0, and the real impedance of the source sees purely real and identical load impedance. Note...
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