A Precision Current Source Using $\Delta$– $\Sigma$ Modulation

We present a new source for currents in the picoampere range based on the charging of a capacitor at a constant rate. The voltage ramp is generated using Delta-Sigma modulation and low-pass filtering. This method ensures the linearity of the voltage ramp by calibrating a small number of voltage levels prior to generating the current. Our analysis shows that we can calibrate a picoampere meter with a standard uncertainty of less than 20 μA/A at 10 pA.