Multi-channel capacitive sensing circuit

• US 8,339,148 B2
• Filed: 08/24/2007
• Issued: 12/25/2012
• Est. Priority Date: 07/19/2007
• Status: Expired due to Fees

• Current Assignee: Barun Electronics Co., Ltd.
• Original Assignee: Barun Electronics Co., Ltd.
• Inventors: Ahn, Taedong
• Primary Examiner(s): Dole, Timothy J
• Assistant Examiner(s): ALLGOOD, ALESA M
• Application Number:
  US12/669,493
• Publication Number:
  US 20100188106A1
• Time in Patent Office: 1,950 Days
• Field of Search: 324/663, 324/678, 324/530, 324/683, 324/686, 324/519, 324/750.17, 324/754.28, 324/658, 737/80
• US Class Current: 324/678
• CPC Class Codes: G01D 5/24 by varying capacitance

Abstract

Provided is a multi-channel capacitive sensing circuit, in which at least one capacitive sensor has the capacitance changed corresponding to the change of external environment, and generates change signals corresponding to the capacitance change, respectively. An oscillator outputs a carrier wave modulating the capacitance change signal. At least one capacitance-to-voltage converter receives the capacitance change signals modulated by means of the carrier wave and outputs voltage signals corresponding to the modulated capacitance change signals, respectively. A multiplexer receives the voltage signals, selects any one of the voltage signals and sequentially outputs them. An analog-to-digital converter (ADC) receives the voltage signals outputted from the multiplexer, converts them into digital voltage signals and outputs them. Accordingly, it is possible to output the capacitance change signals each generated in the at least one capacitance sensor to one ADC using the multiplexer. As a result, it is possible to reduce the size of the multi-channel capacitive sensing circuit and reduce the power consumption.

Claims

1. A multi-channel capacitive sensing circuit comprising:

at least one capacitive sensor having capacitance changed corresponding to the change of external environment and generating capacitance change signals corresponding to the capacitance change, respectively;

an oscillator outputting a carrier wave modulating the capacitance change signal;

at least one capacitance-to-voltage converter each receiving the capacitance change signals modulated by means of the carrier wave and outputting voltage signals corresponding to the modulated capacitance change signals, respectively;

a multiplexer receiving the voltage signals and selecting any one of the voltage signals to sequentially output it; and

an analog-to-digital converter (ADC) receiving the voltage signals outputted from the multiplexer, converting the voltage signals into digital voltage signals and outputting them,

wherein each of the at least one capacitive sensor comprises a first capacitor and a second capacitor whose capacitances are changed by different amount with respect to the change of external environment,

wherein the oscillator is electrically connected to the first and second capacitors and outputs the carrier wave to the first and the second capacitors,

wherein the oscillator is a chopper oscillator, and

further comprising an inverter electrically connected to the oscillator and the second capacitor, receiving the carrier wave, and outputting an anti-phase carrier wave having a phase opposite to that of the carrier wave.

2. The multi-channel capacitive sensing circuit according to claim 1, wherein the carrier wave is a square wave.

3. The multi-channel capacitive sensing circuit according to claim 1, wherein each of the at least one capacitance-to-voltage converter comprises an operational amplifier and a capacitor.

4. The multi-channel capacitive sensing circuit according to claim 3, further comprising a switch electrically connected to the negative input terminal of the operational amplifier and the output terminal of the operational amplifier and repeating on/off operations at predetermined intervals.

5. The multi-channel capacitive sensing circuit according to claim 1, further comprising a digital demodulator demodulating the digital voltage signals from the ADC and outputting the demodulated voltage signals.

6. The multi-channel capacitive sensing circuit according to claim 5, wherein the digital demodulator sequentially multiplies the demodulated voltage signals by +1 and −

1 at the same period as that of the carrier wave.

7. The multi-channel capacitive sensing circuit according to claim 5, wherein the ADC performs oversampling.

8. The multi-channel capacitive sensing circuit according to claim 7, further comprising a decimator receiving the demodulated voltage signals, decimating them with a decimation ratio of 1/k and outputting them.