Invention Grant
US09551738B2 Robust capacitive measurement system 有权
坚固的电容测量系统

Robust capacitive measurement system
Abstract:
A capacitive sensing circuit is disclosed, wherein the mixer is directly connected to the sense electrode. The AC transimpedance amplifier in front of the mixer in prior art is removed and replaced by a differential DC transimpedance amplifier respectively integrator.The mixer DC offset voltage or current together with the large amplification factor required after the mixer now would result in an inacceptable DC offset at the output of the signal chain. In order to eliminate the effect of the mixer offset, the amplifying stages after the mixer are AC coupled to the mixer output and one of the signals entering the mixer is phase modulated or amplitude modulated with a known low frequency signal. An additional mixer after the AC coupled amplifying stages is driven with the same low frequency modulating signal, resulting in the wanted DC output signal responsive to the capacitance to be measured.
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