Living body detection method and apparatus

An electronic circuit arrangement for detection of electrical contact of a living body with a contact surface, wherein the living body has electrical characteristics resembling an impedance network comprising a first impedance portion, a second impedance portion and a third impedance portion connected in series;

• wherein the first impedance portion comprises a first capacitor of a first capacitance value and a first resistor of a first resistance value connected in parallel to form a first impedance bridge, the second impedance portion comprises a second capacitor of a second capacitance value and a second resistor of a second resistance value connected in parallel to form a second impedance bridge, and the third impedance portion comprises a third capacitor of a third capacitance value and a third resistor of a third resistance value connected in parallel to form a third impedance bridge;
• and wherein the impedance network has a characteristic charge rise-time and a characteristic discharge fall-time;
• wherein the electronic circuit arrangement comprises a solid-state controller, a non-volatile data storage device, a probing signal source and a responsive signal collector:
• wherein the signal source is to generate a probing pulse or a train of probing pulses as a probing signal, and to transmit the probing signal to contact terminals;
• wherein the responsive signal collector is for collecting a responsive signal at the contact terminals, the responsive signals being signals generated in response to or in reaction to the probing signal acting on the contact terminals;
• wherein the probing pulse comprises a probing pulse base state at a probing pulse base state voltage, a probing state at a probing state voltage and a probing pulse intermediate state having intermediate voltages;
• wherein the probing pulse rises from the probing pulse base state voltage to the probing state voltage in a rise-time which is a probing pulse rise time, stays in the probing state for a duration which defines a probing state duration, returns to the probing pulse base state at the end of the probing state, and stays in the probing pulse base state for a probing base state duration until end of the probing pulse;
• wherein the intermediate voltages of the probing pulse intermediate state increase with time when the probing pulse changes from the probing pulse base state to the probing state;
• wherein the probing pulse and the impedance network are related or characterized such that when the probing pulse is applied on the impedance network, an expected response pulse comprising an expected pulse base state having an expected pulse base magnitude and pertinent electrical characteristics is expected, wherein the pertinent electrical characteristics comprises an expected pulse peak, an expected pulse steady state and an expected pulse transition state interconnecting the expected pulse peak and the expected pulse steady state;
• wherein the expected pulse peak has an expected pulse signal magnitude, the expected pulse peak signal magnitude being an electrical parameter bearing or having a correlation between the probing state voltage and the second resistance value;
• wherein the expected pulse steady state has an expected steady state signal magnitude, the steady state signal magnitude bearing or having a correlation between the probing state voltage and sum of resistance values of the resistors of the impedance network;
• and the expected pulse transition state has a fall time or fall-time characteristics commensurate with or corresponding to the characteristic discharge fall-time of the impedance network;
• and wherein the controller is to capture a plurality of electrical parameters of the responsive signal at a plurality of capture times, to determine with reference to the captured electrical parameters whether the responsive signal comprises a response pulse having the pertinent electrical characteristics of or corresponding to the expected response pulse, and to send out a control signal indicative of positive living body detection upon a positive outcome of determination.