PAPER SESSION 3: MODULATION AND CONTROL
35 DiscreteTime Modeling of ContinuousTime Pulse
Width Modulator Loop
Lars Risbo. Texas
Instruments Denmark, Lyngby, Denmark
Traditionally, the dynamics of continuoustime PWM
loops are analyzed by using linearized continuoustime
models where the comparator is modeled as a linear
gain. However, this method fails to accurately explain
several important characteristics such as noise aliasing,
image components, and loop stability. This paper
analyzes the sampling nature of the comparator and
derives a general linear discretetime loop smallsignal
model that can be applied to loops of any order—both
driven (synchronized) and free running (selfoscillating).
