Patent ID: 8264247

Claim:
An electric potential sensor comprising: at least one detection electrode arranged for capacitive coupling with a sample under test and for generating a measurement signal; a sensor amplifier adapted to receive the measurement signal as input and to supply an amplified detection signal as output; input impedance enhancing means comprising at least one of a guard circuit, a bootstrapping circuit and a neutralisation circuit, said input impedance enhancing means providing a high input impedance to the sensor amplifier for increasing the sensitivity of the electrode to reduced electric potentials; a discrete pre-amplifier stage for increasing the amplitude of the measurement signal input to the sensor amplifier, the discrete pre-amplifier stage comprising a further amplifier arranged to co-operate with the sensor amplifier so as to reduce an input capacitance of the sensor amplifier, whereby to enhance signal measurement in instances where capacitive coupling between the sample under test and the detection electrode is equal to or less than the input capacitance of the sensor amplifier; and means for reducing noise amplitude in order to increase signal to noise ratio, the means for reducing noise amplitude comprising at least one of a DC stability gain setting circuit comprising means for introducing AC coupling into a network for setting the gain of the sensor amplifier, a noise matching circuit comprising means for balancing the impedance at inverting and non-inverting inputs of the sensor amplifier, and an enhanced bootstrapping circuit comprising a bootstrapping circuit including gain setting means providing feedback from the output of the sensor amplifier to an input thereof.