Accurate design of charge pump circuits from model to silicon. Development of multistage system in package devices for battery powered applications

Resumen

Charge pump circuits are part of any power management IC portfolio. They can be designed through several inductor-less topologies and use capacitors as energy storage elements to obtain higher (or lower) output voltage levels from a primary input voltage source. One of these topologies is the Two-Phase Voltage Doubler (TPVD). However, designing a charge pump circuit based on the TPVD structure (or any other topology) is not as easy as it seems. The size of the switching transistors, the values of the flying and load capacitors, the operating frequency of the switching clock signals, the input voltage value, and the current required by the output load are design/operating parameters that have a direct influence in the steady-state output voltage value obtained by the charge pump circuit. Hence, large and slow parametric SPICE-based simulations must be carried out in order to find out which are the values of the design/operating parameters that fulfil the output requirements. On the other hand, the efficiency of such circuits decreases dramatically when working in a light-load scenario.Thus, this fact becomes a serious drawback that must be overcome, especially in battery-powered hardware applications where autonomy is a critical design constraint to be taken into account. This thesis work presents the full conception, design and implementation of a novel design platform (library of components + numerically-based simulation model) ready to be used by any analog IC engineer to develop single or multi-stage charge pump designs based on the TPVD topology. The library of components is formed by all the internal circuitry needed to make the TPVD structure work (non-overlapping clock generators, regulator, ripple minimization system, soft start-up circuit and high-voltage level shifters). Also, an accurate compact mathematical model to be applied in the steady-state analysis of single or multi-stage TPVD designs is also included. The simulation of this model through numerical computing software tools provides a full understanding about the voltage doubler's steady-state output behaviour while, at the same time, accelerates and simplifies the design process of such circuits in comparison with the use of classical parametric SPICE-based simulations. Numerically simulated results show that the data provided by the proposed model is closer to the SPICE-based simulation data than the data provided by any other existing model, offering less than 1% of relative error over a wide range of working load conditions