Circuit Q factor as a basic but still ambiguous index for resonators and oscillators
Everyone agrees that Q factor is a key objective function in designing RF resonators and oscillators. Nevertheless, students, circuit engineers, and even microwave professors often encounter difficulties due to ambiguity in Q factor formulas. There are at least seven possible different ways to define Q factor based upon: 1) fractional 3 dB bandwidth; 2) power dissipation ratio to stored energy; 3) reflection phase to frequency slope; 4) dc power supply pushing figure; 5) output load pulling figure; 6) Leeson's sideband noise spectrum; and 7) Adler's injection locking range. We have to choose the right formula depending on the target of each development. The lecture explores the world of Q factors by giving their physical meanings and schematic examples. The formulas to be shown in the lecture are fundamental and so persuasive that the audience can apply with just a pencil and paper.