Cam cell, cam device and operation method thereof, and method for searching and comparing data

A content addressable memory (CAM) device, comprising:

• a plurality of CAM cell strings, wherein each of the CAM cell strings comprises a plurality of CAM cells, each of the CAM cells comprises a plurality of serial-coupled flash memory cells, and individual storage data of each of the CAM cell strings is related to a portion of a reference string data;
• a word line decoder and driver configured to provide a plurality of search voltage to the CAM cells, wherein in a plurality of comparison rounds, the word line decoder and driver determines the search voltages applied on the CAM cells according to a data read;
• a plurality of matching lines coupled to the CAM cells;
• a plurality of sense counting circuits coupled to the matching lines;
• and
• a decoder coupled to the sense counting circuits;
• wherein
• in the comparison rounds, when the search voltages are applied on the CAM cells, the sense counting circuits sense and count a plurality of matching currents on the matching lines to generate a plurality of counting results;
• and the decoder determines whether the data read matches the reference string data according to the counting results of the sense counting circuits;
• when the storage data is selected among a plurality of predetermined storage data, a first threshold voltage of the first flash memory cell and a second threshold voltage of the second flash memory cell are selected among a maximum threshold voltage value or a minimum threshold voltage value, or the first threshold voltage and the second threshold voltage both are greater than or equivalent to the maximum threshold voltage value.