1. A method for analog-to-digital conversion, comprising: providing the plurality of pipelined analog-to-digital converters (ADCs), wherein respective inputs of the pipelined ADCs are electrically connected to a same analog signal; utilizing the pipelined ADCs to perform analog-to-digital conversion on the analog signal; receiving digital outputs generated by the pipelined ADCs performing analog-to-digital conversion on the analog signal; and performing digital calculations on the digital outputs to generate a calibrated digital output, comprising: providing a plurality of digital calculation paths respectively corresponding to the pipelined ADCs; for each digital calculation path corresponding to an associate pipelined ADC of the pipelined ADCs, performing an adaptive processing according to a difference between latest values of respective outputs of the digital calculation paths, in order to generate at least latest digital estimation values of gain values of a plurality of stages of the associate pipelined ADC; for each digital calculation path corresponding to the associate pipelined ADC of the pipelined ADCs, performing a digital code combination on at least the latest digital estimation values of the gain values and respective digital codes of an associated digital output corresponding to the associate pipelined ADC, in order to perform calibration on the digital calculation path, wherein the digital codes correspond to the stages of the associate pipelined ADC, respectively; and averaging latest values of the respective outputs of the digital calculation paths to generate the calibrated digital output.