CPU belongs to the digital circuit, it is the central processing unit, also known as the microprocessor. It is composed of logical operation components, control components, registers. It can only recognize the binary information of the digital circuit, it can perform logical operations and arithmetic operations, and it can also store information.
If the analog signal is to be input to the CPU, the analog quantity must first be converted into a digital quantity in order to communicate with the CPU information. These are analog circuits do not have.