Dual-Ramp A/D Converter Error Due to Nonideal Integrator Capacitor

It is shown that very high accuracy hybrid packaged dual-ramp analog-to-digital converters can be built using ceramic NPO-type chip capacitors that exhibit a dielectric absorption specification of 0.75 percent. Capacitor recovery voltage is shown versus time for several 0.01-/g-m/F NPO-type ceramic capacitors. An absorptive capacitor model for the NPO capacitor is shown. Typical component values for an absorptive model of an 0.01-/g=m/F NPO capacitor are determined. The worst case integrator error due to dielectric absorption in a particular synchro-to-digital converter utilizing two dual-ramp converters with 0.01-/g=m/F integrator capacitors is shown to be in the order of microvolts.