Low-power contactless physiological sensor

A system-on-chip contactless physiological sensor comprising:

• a capacitive-sensor electrode having a first capacitance;
• an amplifier device connected to the capacitive-sensor electrode, the amplifier device having an inverting input and non-inverting input, the capacitive-sensor electrode and the amplifier device at least in part forming an amplifier circuit for the physiological sensor which has a gain determined by the values of a second capacitance of an artefact-reducing capacitor and a third capacitance of a bridging capacitor which spans the amplifier device between the inverting input and an output of the amplifier device;
• and
• the artefact-reducing capacitor being connected in series between the capacitive-sensor electrode and the inverting input of the amplifier device;
• wherein the second capacitance is less than the first capacitance;
• wherein there is no impedance boosting input between the capacitive-sensor electrode and the inverting input of the amplifier device, and wherein the gain of the amplifier device is determined by the formula:
• gain
• =
• C
• ⁢
• 1
• ⁢
• C
• ⁢
• 2
• (
• C
• ⁢
• 1
• +
• C
• ⁢
• 2
• )
• C
• ⁢
• 3
• =
• C
• ⁢
• 1
• 1
• +
• C
• ⁢
• 2
• C
• ⁢
• 1
• C
• ⁢
• 3
• ≅
• C
• ⁢
• 2
• C
• ⁢
• 3
• where C1 is the first capacitance, C2 is the second capacitance, and C3 is the capacitance of the bridging capacitor.