Sensor switch with spread spectrum sensing signal and synchronous rectifier

A capacitive sensor comprising:

• a sensor electrode, a signal generation circuit, and a signal evaluation circuit;
• wherein the sensor electrode is connected to the signal generation circuit configured to generate an output signal to the sensor electrode;
• and
• wherein the sensor electrode is connected to the signal evaluation circuit configured to evaluate an input signal acquired from the sensor electrode,
• the signal generation circuit comprising a signal generator chosen to be one of a noise generator, a pseudo-noise generator, a chirp signal generator, and a frequency sweep signal generator,
• the signal evaluation circuit comprising a synchronous rectifier,
• the synchronous rectifier comprising a first switch, and a second switch, wherein the first switch and the second switch are connected to the signal generator and configured for alternating switching in phase with the input signal, and
• wherein each of the signal generation circuit and the signal evaluation circuit refers to a circuit ground,
• the capacitive sensor further comprising:
• a first low pass filter, a second low pass filter, and
• a microcontroller that incorporates the first switch, the second switch, a first input ADC, a second input ADC,
• wherein the signal evaluation circuit comprises the first switch connected to the first input low pass filter that is external to the microcontroller, the first input low pass filter being further connected to the first input ADC,
• wherein the signal evaluation circuit comprises the second switch connected to the second input low pass filter that is external to the microcontroller, the second input low pass filter being further connected to the second input ADC,
• wherein the signal evaluation circuit comprises a difference calculator configured to subtract outputs of the first input ADC and the second input ADC.