Measuring closed loop stability with bode plots And lower gain at higher frequencies means better noise immunity or lower output ripple. For example, a higher 0 dB crossover frequency usually means a faster response to load changes. In addition to safety considerations, performance is also affected by values that can be determined from Bode plots. A typical goal for phase margin is to have at least 45 degrees, and even higher values might be desirable in more critical applications. A loop with a gain margin of zero or even less would only be conditionally stable and could easily become unstable if gain changed. The greater the distance or margin the better, because higher gain and phase margins mean greater stability.

Gain and phase margins represent the distance from the points at which instability could occur. These values, 0 dB and -180° are important because system instability occurs if these two values meet. Gain margin indicates the distance, in dB, from the measured gain to a gain of 0 dB. Gain margin, on the other hand, is measured at the frequency where the phase shift equals -180°. In other words, how many degrees the phase must be decreased in order to reach -180°. Phase margin is a measure of the distance from the measured phase to a phase shift of -180°.

This is commonly referred to as the “crossover frequency”. Phase margin is measured at the frequency where gain equals 0 dB.

Bode plot multisim decade