Patent ID: 8130022
Filing Date: 2012-03-06
Classification: H03K

Abstract:
1. A system to achieve a switch interface circuit consuming a few tens of nanoamps, whilst a push-button switch is closed, having low impedance input when the switch is open in order to eliminate RFI interference, and to allow for extended switch-closed operation is comprising: a push-button switch having a first terminal connected to a positive supply, wherein its second terminal is connected to an input of a Schmitt trigger inverter having hysteresis, to a first terminal of a first resistive element and to a first terminal of a second resistive element; said positive and a negative supply voltage; said first resistive element wherein its resistance is in the order of MΩs, having its second terminal connected to the negative supply voltage; said second resistive element wherein its resistance is in the order of kΩs, having its second terminal connected to a drain of an NMOS transistor; said NMOS transistor having its source connected to the negative supply voltage and its gate connected to an output of said Schmitt trigger inverter enabling to sense asynchronously any time a switch transition from open to close; said Schmitt trigger inverter; one logic inverter having its input connected to the output of said Schmitt trigger inverter and having its output connected to a clock input of a D-type flip-flop; and said D-type flip-flop wherein its output is the output of said switch output circuit and its data input is always at a logical “1” state.