英語 での Phase margin の使用例とその 日本語 への翻訳
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As the pole is moved out in frequency, the phase margin increases.
Loop response with 90° of phase margin is that of an exponential, single pole.
MATLAB step() command for closed-loop gain for varying phase margin.
At a phase margin of around 72° the recovery is the fastest with 0% overshoot.
The rule of thumb is tohave at least 45 degrees of phase margin at unity gain.
As the phase margin decreases below 90°, the real portion of the loop gain becomes negative.
If this pole is brought in too low in frequency, the phase margin begins to reduce.
The phase margin drops dramatically, and it can make the system unstable even with Type ΙΙΙ compensation.
The measured plots show a crossover frequency of 65kHz and phase margin of 52.8 degrees.
The phase margin and crossover frequency can be inferred from an observed waveform, but a frequency response analyzer(FRA) is convenient.
Then ω1 and ω2 are adjusted to vary the phase margin while maintaining the same crossover frequency.
A higher overall gain also improves stability by decreasing the bandwidth andincreasing the phase margin of the feedback loop.
The single-pole loop which results in a 90° phase margin is a conservative approach for the loop gain at crossover.
The open-loop gain andphase plot from the model shows a crossover frequency of about 70kHz and a phase margin of 56 degrees.
The first-order model would have predicted a phase margin of about 90 degrees, and may have implied that wider component tolerance was acceptable.
If a transient response characteristic does not satisfy demands,the feedback loop phase margin and gain margin should be adjusted.
Unfortunately, this pole decreases the phase margin, causing unwanted peaking in the frequency response and ringing in the step response.
The closed-loop Bode plot of the control loop in Figure 11shows a 19.4kHz unity-gain frequency with 59° phase margin. Figure 11.
It can measure characteristics(phase margin, gain margin) of the control circuit, resonance frequency of the structure, and impedance, etc.
The higher the boost, the more positive feedback is applied,giving rise to reduced phase margins and increased closed-loop distortion.
However, that the phase margin obtained in practice is far less than 90 degrees depending on choice of crossover frequency, operating duty cycle, and amount of slope compensation used.
This causes the step response in the time domain to show overshoot,and eventually ring as the phase margin gets closer and closer to 0°.
Important points in performing evaluations were described above; the phase margin and crossover frequency can always be inferred from an observed waveform, but this is fairly troublesome.
PLLs use a negative-feedback control system similar to that of an amplifier,so the concepts of loop bandwidth and phase margin apply here as well.
Procedure for Predicting the Phase-Margin Following is a description of a control-loop design procedure for the MAX1954A current-mode controller that considers this high-frequency effect andpredicts the phase margin accurately.
The well designed package of the ADA4927-1 allows for a simple layout that reduces parasiticcapacitance in the feedback path that can erode the phase margin of the amplifier.
Looking at the control loop in the frequency domain,AC loop analysis enables direct measurement of the control-loop bandwidth and phase margin going back to our human health example, this step is like taking a patient's blood pressure.
The following application note describes a control-loop design procedure for the MAX1954A current-mode controller that considers this sampling effect andaccurately predicts phase margin.
With added external slope compensation, the shape of the gain and phase curves do not change,but the amplitude of the gain will decrease and phase margin will increase.
In adjustments, there is a general tendency for stability to be reduced when the response is made more rapid, and so adjustments should be made so as toobtain the earliest response while maintaining the phase margin.