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楼主 |
发表于 2007-5-23 09:10:41
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key points of this paper are:
1) A system should only be analyzed for stability using the Bode plot, if it has at most one phase crossover frequency. Additionally, if it has only one gain crossover frequency and the amplitude ratio as well as the phase angle are decreasing at the gain crossover and afterward, then the gain and phase margins can be calculated in a way found in control textbooks.
2) A system that has only one phase crossover frequency but multiple gain crossover frequencies is stable if the amplitude ratios, corresponding to frequencies where f= -180∞-n*360∞, are all less than unity and the open-loop system is stable. The gain margin is calculated from the crossover frequency or a frequency corresponding to a larger n, whichever exhibits the largest amplitude ratio.
3) If the Bode plot information is inconclusive, the Nyquist stability criterion should be applied for stability analysis of closed-loop systems.
Fortunately, systems in analog circuits are usually not pathological, so bode plot works well.
but if you are an aggressive and creative designer, you'd better pay more attention to your stability
checking approach. Sometime bode plot might cheat you.
Best Regards,
River |
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发表于 2007-5-21 16:26:41
