Circuit for acquisition of the capacitance or capacitance change of a capacitive circuit element or component

• US 6,194,903 B1
• Filed: 12/02/1997
• Issued: 02/27/2001
• Est. Priority Date: 01/21/1996
• Status: Expired due to Term

• Current Assignee: I F M Electronic GmbH
• Original Assignee: I F M Electronic GmbH
• Inventors: Schulz, Jörg
• Primary Examiner(s): Metjahic, Safet
• Assistant Examiner(s): Nguyen, Vincent Q.
• Application Number:
  US08/982,483
• Time in Patent Office: 1,183 Days
• Field of Search: 324/672, 324/674, 324/676, 324/677, 324/679, 324/681, 324/684, 324/686, 324/660, 324/661, 340/870.37
• US Class Current: 324/661
• CPC Class Codes: G01D 5/24 by varying capacitance
• CPC Class Codes: G01R 27/2605 Measuring capacitance capacitive sensors G01D5/24
• CPC Class Codes: H03K 17/955 using a capacitive detector
• CPC Class Codes: H03K 2217/960725 Charge-transfer
• CPC Class Codes: H03K 2217/960745 Capacitive differential; e.g. comparison with reference capacitance
• CPC Class Codes: H03K 2217/96075 involving bridge circuit

Abstract

A circuit for acquisition of the capacitance or capacitance change of a capacitive circuit component with a clock generator (1), changeover contact (2) controlled by the clock generator (1), a storage capacitor (3), a voltage source (4), and an evaluation stage (5). An electrode of the capacitive circuit component is connected to the input (7) of the changeover contact (2), a first output (8) of the changeover contact (2) is connected to a first electrode of the storage capacitor (3), a first electrode of the storage capacitor (3) is connected, on the one hand, via a resistance network (9) to the voltage source (4), and on the other hand, to the evaluation stage (5). The second electrode of the storage capacitor (3) is connected to a reference potential (10). In a first aspect of the invention, the circuit can compensate for disruptive influences especially well by the evaluation stage (5) being suitable for current evaluation with essentially no voltage excursions occurring on the changeover contact (2). According to a second aspect of the invention, the evaluation stage (105) is suitable for voltage evaluation and the resistor network (108) is adjustable.

Claims

1. Circuit for a capacitive circuit component comprising a clock generator, a first changeover contact having an input and first and second outputs, and being controlled by the clock generator, a sensor capacitor, a first storage capacitor having first and second electrodes, a first resistance network, a voltage source, and an evaluation stage;

wherein an electrode of the sensor capacitor of the capacitive circuit component is connected to the input of the changeover contact, the first output of the first changeover contact is connected to the first electrode of the first storage capacitor, the first electrode of the first storage capacitor is connected via the first resistance network to the voltage source and is also connected to the evaluation stage, and the second electrode of the first storage capacitor is connected to a reference potential;

wherein the evaluation stage is a current evaluator and essentially no voltage excursion occurs on the first changeover contact.

2. Circuit as claimed in claim 1, wherein said evaluation stage comprises a difference current amplifier, and wherein a microprocessor is series connected to the difference current amplifier.

3. Circuit as claimed in claim 1, further comprising an auxiliary voltage which is synchronized with a changeover frequency of the clock generator and which is applied to the capacitive circuit component.

4. Circuit as claimed in claim 3, wherein means for temporarily turning off the auxiliary voltage, thereby enabling the evaluation stage to generate a compensation measured value from a measured value which then remains.

5. Circuit as claimed in claim 3, wherein the auxiliary voltage is a modulated voltage.

6. Circuit as claimed in claim 3, wherein said auxiliary voltage is coupled via an external probe structure to the capacitive circuit component.

7. Circuit as claimed in claim 3, wherein said auxiliary voltage is coupled via an internal coupling capacitor to the capacitive circuit component.

8. Circuit as claimed in claim 1, further comprising a reference capacitor, a second changeover contact having an input and first and second outputs and being controlled by the clock generator, a second storage capacitor having first and second electrodes, and a second resistance network;

wherein an electrode of the reference capacitor is connected to an input of the second changeover contact, a first output of the second changeover contact is connected to the first electrode of the second storage capacitor, the first electrode of the second storage capacitor is connected via the second resistance network to the voltage source and is also connected to the evaluation stage; and

wherein the second electrode of the second storage capacitor is connected to a second reference potential.

9. Circuit as claimed in claim 8, wherein the second output of the first changeover contact is connected to the first output of the second changeover contact;

and wherein the first output of the first changeover contact is connected to the second output of the second changeover contact.

10. Circuit as claimed in claim 8, wherein the second output of the first changeover contact and the second output of the second changeover contact are each connected to the reference potential.