Apparatus and method of direct current sensing from source side in a virtual ground array

An apparatus for direct current sensing from the source side of memory elements in a virtual ground array, the apparatus comprising:

• a virtual ground array consisting of select gates selectable by select gate lines, memory elements having a source and a drain, the memory elements selectable by word lines and at least two of the select gates and arranged in series along the word lines, local bitlines connecting the select gates with the memory elements, and global bitlines connecting the select gates with the comparator, and arranged such that sets of memory elements are selected in pairs along each word line by two partially overlapping pairs of select gates, wherein an output of the virtual ground array is direct current from the source of selected memory elements and the pairs of select gates and associated global and local bitlines are operative to set the drain of the selected memory elements to a set potential;
• at least one multiplexor connected with the virtual ground array and the comparator that selects one of the selected memory elements as the origin of direct current input to a sense load and at least one column decoder connected with the set of memory elements and the comparator operative to decode the set of memory elements;
• and
• a comparison circuit containing a reference circuit that contains a source of a reference current and a reference load to transform the reference current into a reference voltage, the sense load to transform a direct current from the virtual ground array into a sense voltage, and a comparator comparing the reference voltage and the sense voltage.

A method of direct current sensing from the source side of memory elements in a virtual ground array, the method comprising:

• selecting a set of memory elements having a source and a drain contained in the virtual ground array;
• comparing a direct current obtained from the source of a selected memory element contained in the set of memory elements with a reference current from a reference circuit via a comparator;
• and
• determining the direct current using an output of the comparator,
• the virtual ground array comprising memory elements, select gates, select gate lines connected with the select gates, word lines, global bitlines, and local bitlines connecting the select gates with the memory elements, wherein the word lines and at least two of the select gates select the set of memory elements and the global bitlines connect the select gates with the comparator.