拉扎维《模拟集成电路设计》第二版课件 Ch10.ppt

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Systems with Multiple 180 degree Crossings If crosses 180 degree an even(odd) number of times while , then the system is stable(unstable). * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Slewing Study For large A For circuit in (b) - CF acts as a short circuit - The slope reveals Miller Effect at the output - I1 only serves as the bias current * Slewing in Two-Stage Op Amp Positive slew rate if M5 is not wide enough, M1 goes to triode Negative slew rate - Vx rises to turn off M5 - M3 goes to triode * Example 10.8 Op amps typically drive a heavy load capacitance. Repeat the slew rate analysis. Solution: Case(a) Case(b) Recall class-AB op amp incorporate Miller compensation, degrading the phase margin. Slower than class-A Op Amp Current mirror yields Slewing rate * Slewing in Two-Stage Class-AB Op Amp * Source Follower to Remove Zero Expect left-plane-zero at higher frequency * Common-gate to Remove Zero Source follower limits lower end output Further splitting provides more bandwidth * Common-gate to Remove Zero Slew Rate Positive slewing Negative slewing I3, I2 must as large as Iss * Two-Stage Cascode Op Amp Zero Dominant pole Non-dominant pole It is plausible to combine two methods and the capacitance at X is quite large, which should also be taken into consideration * Nyquist’s Stability Criterion Bode plot only consider simple sinusoid waveform Nyquist’s stability criterion exams RHP poles. is a growing sinusoid could lead to unstable state Nyquist stability analysis predicts how many zeros has in the right half plane(RHP) or on the jw axis. * Basic Concepts Plot H function in polar coordinates by angle and radius; With frequencies vary, they create a contour. The horizontal and vertical axes are two projections