Digital input circuit and method for high voltage sensors

A digital input circuit comprising:

• a series connection of a first current limiter and switch coupled between a signal input and ground, wherein the switch has a switch control input;
• and
• a logic level shifter coupled to the signal input and having a first switch control output coupled to the switch control input and a signal output, where a maximum amplitude at the signal input is greater than a maximum amplitude at the signal output;
• wherein the logic level shifter includes a current comparator having a current input coupled to the signal input and a current output and a second current limiter coupling the input of the current comparator to ground, wherein the first current limiter has a higher current limit than the second current limiter, and wherein the logic level shifter includes a voltage comparator having an input coupled to the signal input and an output coupled to the switch control by a one-shot monostable multivibrator.

A digital input method comprising:

• comparing an input signal to a reference threshold voltage
• activating a one-shot monostable multivibrator when the input signal exceeds the reference threshold voltage;
• coupling the input signal to ground with a current limiter by closing an electronic switch that is controlled by the activation of the one-shot monostable multivibrator;
• providing an output signal responsive to the input signal, where a maximum amplitude of the input signal is greater than a maximum amplitude of the output signal, by latching the output signal while the input signal is above a threshold voltage;
• and
• opening the electronic switch after the output signal is latched.