Dual-slope analog-to-digital converter with voltage to current converter

Claim 1

An analog-to-digital signal converter having a first analog signal input region and having a plurality of digital signal output regions, said converter comprising: a first and second multiplexing means each having a plurality of input regions including a first input region and each having an output region which can be electrically connected to a selected one of its said input regions, said first multiplexing means first input region being electrically connected to said first analog signal input region, and said second multiplexing means first input region being electrically connected to a first terminal means adapted for electrical connection to a first voltage source: an analog conversion means having first and second input regions and having first and second output regions, said analog conversion means if electrically energized being capable of providing an electrical current output flow, through any circuit components capable of permitting such a current flow therethrough that are electrically connected between said analog conversion means first and second output regions, in response to any differences in voltages applied to said analog conversion means first and second input regions and in a direction depending on that polarity taken by any such differences, said analog conversion means first input region being electrically connected to said first multiplexing means output region, and said analog conversion means second input region being electrically connected to said second multiplexing means output region; first and second connection means each having first and second terminating regions between which a conductive path can be provided of a selected conductivity, said first connection means first terminating region being electrically connected to said analog conversion means first output region, and said second connection means first terminating region being electrically connected to said analog conversion means second output region; a capacitor means having first and second terminating regions between which electrical capacitance of a selected value is present, said capacitor means first terminating region being electrically connected to said first connection means second terminating region, and said capacitor means second terminating region being electrically connected to said second connection means second terminating region; third and fourth connection means each having first and second terminating regions between which a conductive path can be provided of a selected conductivity, said third connection means first terminating region being electrically connected to said capacitor means first terminating region, and said fourth connection means first terminating region being electrically connected to said capacitor means second terminating region; a comparator means having a first input region which is capable of a relatively high circuit impedance, a second input region which is capable of a relatively high circuit impedance, and an output region, said comparator means being capable of providing an output voltage of substantially a selected first value at said comparator means output region if a voltage signal having a value less than a selected first threshold value is provided between said comparator means first and second input regions, and being capable of providing an output voltage of substantially a selected second value at said comparator means output region if a voltage signal having a value exceeding said first selected threshold value is provided at said comparator means first and second input regions, said comparator means first input region being electrically connected to said third connection means second terminating region, and said comparator means second input region being electrically connected to said fourth connection means second terminating region; and a control and timing means having an input region and a plurality of output regions including said plurality of digital signal output regions, said control and timing means input region being electrically connected to said comparator means output region, said control and timing means being capable of selecting said first multiplexing means first input region for electrical connection to said first multiplexing means output region for a selected first duration during which said capacitor means can be charged by said analog conversion means in response to any differences in voltages applied to said analog conversion means first and second input regions, and thereafter being capable of selecting said second multiplexing means first input region for electrical connection to said second multiplexing means output region for a second time duration sufficient to substantially discharge any charge accumulated in said capacitor means during said first time duration, said control and timing means providing a representation of said second time duration at said digital signal outputs.