27.7 A Synthesizable Digital AOT 4-Phase Buck Voltage Regulator for Digital Systems with 0.0054mm2 Controller and 80ns Recovery Time

Achieving a fast-transient response is a major challenge when designing a switching regulator for a processor. Furthermore, high-frequency operation with small passive devices and robust control with a small area footprint in a CMOS-logic process are essential for integrated digital-system voltage regulators. A 4-phase hysteretic converter [1] has a superior transient response using a 3.3V input voltage. However, the analog control circuit under a low input voltage suffers from limited dynamic range. Although a time-based design [2] minimizes the use of analog circuits, it still requires an accurate analog-to-time converter and exhibits only a moderate transient response time. A buck voltage regulator (VR) with a digital controller has been proposed for modern digital systems [3], [4], since it can take advantage of the advanced digital process. However, with a conventional digital proportional-integral-derivative (PID) controller it is difficult to offer high bandwidth due to the large power and chip area of the PID and the required multi-bit ADC. Thus, an additional circuit, the resistive transient assist (RTA), was proposed [4]. This paper presents an all-digital synthesizable VR using a digitally-adaptive on-time (DAOT) controller implemented in a CMOS logic process to achieve a fast recovery time.