“Feedback is so essential that engineers who don’t understand it should be legally barred from circuit design,” said MIT Professor Jim Roberge, stressing the point that a full understanding of feedback is essential to good circuit design.
Many circuit designers think of control system feedback loop compensation only in terms of stability; stable or unstable. Normally we define stability using the bounded-input, bounded-output (BIBO) definition that a system is stable if every bounded input produces a bounded output. Stability is usually measured by two factors shown in the Bode diagram (Figure 1) below, phase margin, which is the difference between actual phase lag and 360° when the loop gain is unity (usually expressed in degrees); and gain margin, which is the amount the gain has fallen below unity when the total phase lag is 360° (usually expressed in dB).
It is instability, rather than the insufficiency of available gain, that usually limits the performance of feedback systems and the white paper shows:
A simple, straightforward method exists for achieving optimum control system performance without trial-and-error. For the full detail please download the Venable Instruments white paper, Optimum Feedback Amplifier Design.