US Patent 9483028 Hybrid analog-to-digital converter

An analog-to-digital converter (ATC) circuit includes a current source; a first amplifier coupled to the current source through a first discharging switch; and a second amplifier coupled to the first amplifier through a second discharging switch; wherein the first amplifier is configured to receive a residue signal of an analog input signal, upon the first discharging switch being turned on, the first amplifier amplifies the residue signal to generate an output signal and simultaneously the current source discharges the residue signal, upon the second discharging switch being turned on, the second amplifier detects when the output signal equals zero so as to determine a discharging time duration of the output signal.