When designing a DC-DC converter, components such as FETs, inductors, current-sense resistors, and output capacitors are carefully selected to match desired output-voltage ripple and transient performance. Following the design of the power stage, closing the loop is necessary.
A DC-DC power supply has a negative feedback loop that uses an error amplifier (EA). A signal that travels in a negative feedback system could encounter poles and zeros through its path. A single pole will decrease a signal phase by ~90° and change the gain slope by –20 dB/Dec, while a single zero will add ~90° to the phase and will increase the gain by +20 dB/Dec.