Circuit techniques for transient response enhancement in linear and low-dropout voltage regulators

Power management ICs are a fundamental component in today's electronic systems. The task performed by power management ICs is to create the different power supply voltage rails from which an electronic system runs. A power management IC acts as an energy transfer buffer or intermediary step between a crude energy source (e.g. battery, charger, mains supply etc) and a useful load (e.g. microprocessor, sensor, filter, etc).;Linear and low-dropout regulators are a key power management module that interfaces with an input voltage source and produces a precise, regulated, and fixed output voltage which is always lower than the input voltage. When the difference between the input voltage and the output voltage is very small, while still maintaining regulation, the linear regulator is said to have a low-dropout capability. Low-dropout capability is particularly useful in maximizing power efficiency in the system.;The transient response of a linear regulator is of critical importance both to a load that is powered from the regulator output as well as the electronic system at large. The main task of a linear regulator is to produce a precisely regulated output voltage irrespective of sudden changes in the load due to load switching. Any substantial disturbance of the output voltage of the regulator can cause such undesired phenomena as inadvertent resets and power-downs. A good transient response must also be achieved with minimum quiescent current overhead to minimize power losses in the system.;Another aspect of the transient response in linear regulators that is also important is the startup response. In certain applications, the voltage regulator must be soft-started and the output voltage gently ramped upon system startup. Soft-starting eliminates inrush currents and the faults they create on power buses.;In this work, circuit techniques for transient response enhancement in linear and low-dropout voltage regulators are investigated. Both load transient response and startup transient response are investigated and circuit techniques are proposed for both cases. Buffer Impedance Attenuation is devised in linear regulators to achieve an enhanced load transient response. In this scheme, the power element in the linear regulator is driven by an impedance-attenuated buffer, and a frequency compensation scheme based on current-buffer compensation is proposed for the control loop. Different soft start circuit techniques are also proposed for linear regulators. The techniques are based unbalanced differential stages, as well as winner-take-all extremum selectors, with the latter being particularly suited for implementation even in bulk CMOS technologies.;The circuit techniques presented in this work are applicable to a wide variety of other applications in power management circuits and systems and are not by any means limited to linear voltage regulators.