Time-Based PWM Controller for Fully Integrated High Speed Switching DC-DC Converters — An Alternative to Conventional Analog and Digital Controllers

This tutorial discusses design of a highly integrated, low quiescent current continuous time PWM controller using time-based signal processing. By virtue of the continuous-time digital nature of the time-based PWM controller, it is capable of achieving very high resolution and speed without using any error amplifier and large compensation capacitor or any high resolution A/D converter and digital PWM while preserving all the benefits of both analog and digital PWM controllers. Using time as the processing variable, the controller operates with CMOS-level digital-like signals but without adding any quantization error. A voltage/current controlled ring oscillator is used as an integrator in place of conventional opamp-RC or Gm-C integrator while a voltage/current controlled delay line is used to perform voltage-to-time conversion. Starting with trade-offs with high speed design of conventional analog and digital PWM controllers, the concept of time based proportional-integral-derivative (PID) controller with complete architecture of a time-based buck converter is presented. The technique was successfully demonstrated on silicon with implementation of 10-25MHz single phase and 30-70MHz 4-phase buck converters on 180nm and 65nm CMOS processes, respectively.