Linear Controller Design: Limits of Performance by Stephen Boyd and Craig Barratt - HTML preview

CHAPTER 7 REALIZABILITY AND CLOSED-LOOP STABILITY

It is far from a simple proposition to employ feedback in this way because of

the very special control required of phase shifts in the amplier and circuits,

not only throughout the useful frequency band but also for a wide range of

frequencies above and below this band. Unless these relations are maintained,

singing will occur, usually at frequencies outside the useful range. Once hav-

ing achieved a design, however, in which proper phase relations are secured,

experience has demonstrated that the performance obtained is perfectly reli-

able.