Robotics: Why do some sensors need analog? Why do some sensors need digital?

MOST SENSORS ARE IN ANALOGY STRUCTURE. THAT WERE HOW THEY WERE DISCOVERED AND MADE.
SENSOR ANALOG SIGNAL IS FUTHER CONVERT INTO DIGITAL FORMAT IF A CPU CIRCUIT AS THE MAIN PARTS FROM DEVICE,BECAUSE CPU ONLY UNDERSTAND DIGITAL SIGNAL.
THERE IS NOT NEED TO CONVERT SENSOR OUTPUT INTO DIGITAL FORMAT IF ANALOG CIRCUIT IS USED.

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