Charge Pump Capacitance Ratio Read Out Design System Approach

This paper presents a design solution for measuring the ratio between different capacitors available in common integrated technology (i.e. MIM, MOM, poly-poly, etc.) by using a Charge Pump (CP) and a system solution approach that defines an alternative self-test operating mode at zero extra die are and cost. Relying on the charge sharing principle, the proposed approach involves two symmetrical structures working in phase opposition and it has been designed in a standard 180-nm CMOS technology. In each of this structure, MIM and MOM capacitors are connected so that, during standard DC-DC boost converter operating mode of the CP, clock pumps result from a sum of the charges coming from both capacitors. During capacitance ratio read out phase, half CP is inhibited while a digital logic controls the initial fly capacitor to be used which determines the amplitude of the first pump. By evaluating it through an input analog chain and repeating this process for the other side, measurements with accuracy of 200ppm over 1% of capacitive variation due to aging or stress effects are reported, regardless the value of the external load.