Modeling and optimization of a latched charge pump loaded by a resistive circuit

Abstract

Many successive improvements of the charge pump (CP) principle introduced by Dickson have paved the way to efficient integrated DC---DC converters. One of the most used CP is the bootstrap Dickson CP, or its double version. However, the best achievement is certainly the latched charge pump (LCP). Indeed, as in a Dickson pump, it makes use of pump capacitors in parallel, lowering its sensitivity to parasitic capacitors and allowing high pump gain. As a double structure, it also exhibits a low output voltage ripple. But one of its best advantages is that it only requires a simple two-phase clock and thus less transistors than the bootstrap CP. Yet, few studies have been published on the LCP. Therefore, this paper focuses on the modeling and design of LCPs. It provides the designer with a simple and robust way to quickly design such a pump when it is meant to be loaded with a resistor and has to deliver a steady-state current. Its optimization in terms of silicon area, efficiency or efficiency-to-area ratio is also discussed. It is shown than contrary to all the previous studies on CP optimization, the total area of the pump, i.e. the area of the capacitors but also the area of the switching transistors have to be considered for a better optimization. Experimental results obtained on a 22 V output voltage CP able to deliver 42 μA, designed in a high-voltage 0.35 μm CMOS technology, are also given.