Analog-to-digital converter

A differential charge transfer analog-to-digital converter comprising:

• a first charge storage location including first and second nodes,
• switch means connected to said second node for connecting said second node to a first input signal in a first position or to a second input signal in a second position;
• detector means connected to said first node for producing an output signal in response to a preselected threshold signal level at said first node;
• means responsive to said output signal connected to said first node for transferring charge into said first charge storage location when said switch means is in said first position until said preselected threshold signal level is reached and for continuing to transfer charge to said charge storage location when said switch means is in said second position until said preselected signal level is again reached;
• and
• means for measuring the amount of charge transferred when said switch is in said second position, the amount of charge being proportional to the difference in magnitude between said first and second input signals.

An analog-to-digital converter comprising:

• charge storage means characterized by linear and nonlinear portions thereof in series circuit relationship;
• first and second differential input terminals adapted to be connected to an input signal source;
• means for connecting said first input terminal to said linear portion of said charge storage location during a first portion of a measurement cycle and for connecting said second input terminal to said linear portion of said charge storage location during a second portion of a measurement cycle;
• means responsive to the level of charge in said nonlinear portion of said charge storage location for providing an output signal responsive to a preselected level of charge in said nonlinear portion of said charge storage location;
• means for transferring charge to said charge storage location during said first portion of said measurement cycle until said output signal is provided, thereby providing zeroing of the converter, and for transferring a measured amount of charge to said charge storage location during said second portion of said measurement cycle until said output signal is again provided, said measured amount of charge being proportional to the difference in voltage applied between said first and second input terminals.