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US 10,378,946 B2Granted
Ink level sensing
AssigneeHewlett-Packard Development Company, L.P.
InventorsNing Ge, Trudy Benjamin, Teck-Khim Neo, Joseph M. Torgerson, Neel Banerjee, George H. Corrigan, III
Life of this patent
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Abstract
In some examples, a method of sensing an ink level includes applying a pre-charge voltage to a sense capacitor to charge the sense capacitor with a charge, sharing the charge between the sense capacitor and a reference capacitor, causing a reference voltage at a gate of an evaluation transistor, and determining a resistance from a drain to a source of the evaluation transistor that results from the reference voltage.
Claims10
An apparatus comprising:
- a sense capacitor between a first node and ground;
- a first switch to couple a first voltage to the first node and charge the sense capacitor;
- a second switch to couple the first node with a second node and share the charge between the sense capacitor and a reference capacitor, causing a second voltage at the second node;
- a transistor having a drain, a gate coupled to the second node, and a source coupled to ground;
- a current source to inject a current at the drain;
- and
- a controller to calculate a resistance between the drain and the source of the transistor based on a voltage at the drain.
4 more elements
Dependencies are inferred from the claim text.