9.6 : 周波数応答

Consider the transfer function in its standard form, with poles and zeros

For a transfer function with a simple zero, the magnitude gain at small frequency values is a straight line with zero slope, and the phase approaches zero.

At the corner frequency, the asymptotic magnitude deviates from the zero-slope line, and the phase approaches 45 degrees.

At higher frequencies, the magnitude plot forms a +20 dB/decade line, and the phase is 90 degrees.

A simple pole is the reciprocal of a simple zero. This means that pole based Bode plots mirror the simple zero plot, reflected about the horizontal axis.

Consider a quadratic pole transfer function.

At lower frequencies, the gain and phase angle approaches zero.

At the corner frequency, the asymptotic magnitude deviation depends on the damping factor, and the phase angle is nearly -90 degrees.

At higher frequencies, the magnitude plot forms a straight line with a slope of -40 dB/decade and a phase of -180 degrees.

For more than one quadratic pole, the slope of the line and phase shift are multiplied by the number of poles.