the content of the sensing, Active shielding for capacitive sensing

February 25, 2023

There are several explanations for fluctuations in these measurements, but the most common root cause is external parasitic capacitance interference. Such interference, such as inadvertently leaning too close to the hand or electromagnetic interference (EMI) in the surrounding area, needs to be brought to our attention and solved in the system design because the interference will greatly reduce the system. Reliability and sensitivity. Fortunately, there are several ways to help alleviate these disturbances so they don't affect the capacitance measurements; one of them is active shielding. The biggest feature of the FDC1004 is that it has a sensing area that reduces interference and helps concentrate the capacitive sensor.

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Imagine having a wire connected to one of the FDC1004 channel inputs. When your hand is near this wire and will be in contact with it, the signal on the hand and the wire forms a closed loop, at which point the human body acts as a ground source. If your hand is not the intended target, then it is considered a parasitic capacitance. The solution is to set up an active shield wrapped around the wire. The shield driver is an active signal output that is driven as a sensor input at the same voltage potential, ie, the same waveform, so there is no potential difference, so there is no capacitance between the shield and the sensor input. Any external interference will couple the shielded signal with minimal interaction to the sensor signal. Figure 1 shows how the shielding of the sensor to the signal line of the FDC1004 reduces the effect of any source of interference on the capacitance measurement.