Patent ID: 9551738
Date: 2017-01-24
CPC Classifications: G01R,H03K

Claim:
1. A capacitive detection system, comprising: an antenna electrode; a first AC signal generator configured to generate a first AC voltage signal, a second AC signal generator configured to generate a second AC voltage signal, said second AC voltage having a lower frequency than said first AC signal, a first mixer for mixing said first AC voltage signal and said second AC voltage signal and for generating a modulated AC voltage signal, wherein said first mixer is operatively coupled to said antenna electrode to apply said modulated AC voltage signal to said antenna electrode, a control and evaluation unit operatively coupled to said antenna electrode, said control and evaluation unit comprising a current measurement circuit configured to measure current signals, said current signals comprising amplitude and/or phase of a current flowing in said antenna electrode, said control and evaluation unit being configured to determine a capacitance to be measured based upon said measured current signals, and to output an output signal indicative of said determined capacitance; wherein said current measurement circuit comprises a differential transimpedance amplifier circuit comprising a common mode voltage setting input, an inverting input, a non-inverting input and an output, wherein said inverting input and said non-inverting input of said transimpedance amplifier circuit are operatively connected to said antenna electrode by means of a multiplexer in such a way that said inverting input and said non-inverting input are alternately supplied with said current flowing in said antenna electrode, said multiplexer being operatively coupled to and controlled by said first AC signal generator.