Distance measurement with capacitive sensor

US8076948B2 · kind B2 · utility

Assignee

• Digital Imaging Systems GmbH · DE

Inventors

• Horst Knoedgen · Munich, DE
• Frank Kronmueller · Neudenau, DE

Key dates

• Filing date: Oct 30, 2008
• Grant date: Dec 13, 2011
• Expiry date: Jul 15, 2030

Classification

• Technology area (CPC G): Physics
• CPC primary: G01D5/24
• WIPO field: Measurement
• WIPO sector: Instruments

Abstract

Circuits and methods to read out capacitive sensors for distance measurement used by a position control system having a high accuracy and low noise have been disclosed. The ratio or difference of the capacitances of two sensor capacitors is used to determine the distance of an object from a target position. A sense amplifier is using auto-zero methods to achieve a long term stability. A sample-and-hold circuit using double correlated sampling methods minimizes noise. Low cost capacitors can be used with the sample-and-hold circuit because not the absolute value of capacitances but only the ratio of capacitances are relevant. A high resolution is ensured also by significant over-sampling of the control loop.