US Patent 9599500 Ink level sensor and related methods

In an embodiment, a method of sensing an ink level includes applying a pre-charge voltage Vp to a sense capacitor to charge the sense capacitor with a charge Q1, sharing Q1 between the sense capacitor and a reference capacitor, causing a reference voltage Vg at the gate of an evaluation transistor, and determining a resistance from drain to source of the evaluation transistor that results from Vg.