Consider next the straight line lab

Consider next the straight line labeled (a) in Fig. 10.43. This line represents a feedback
factor for which 20 log(1/β ) = 85 dB, which corresponds to β = 5.623 × 10−5 and a closedloop
gain of 83.6 dB. Since the loop gain is the difference between the curve and the 1/β
line, the point of intersection X1 corresponds to the frequency at which Using the
graphs of Fig. 10.43, this frequency can be found to be approximately 5.6 × 105 Hz. A more
exact value of 4.936 × 105 can be obtained using the transfer-function equations. At this
frequency the phase angle is approximately −108°. Thus the closed-loop amplifier, for
which 20 log(1/β ) = 85 dB, will be stable with a phase margin of 72°. The gain margin can
be easily obtained from Fig. 10.43; it is 25 dB.