The present application discloses an analog-to-digital conversion (ADC) circuit. The circuit includes an integral circuit including an operational amplifier and an integral capacitor. The circuit further includes a comparator and a timer. The operational amplifier includes a positive input terminal configured to receive a first voltage, a negative input terminal coupled to a signal-collection line configured to collect an analog current signal, and an output terminal configured to output a first output signal. The comparator is configured to compare the first output signal with a second voltage to generate a second output signal to the timer. The timer is configured to start a timing operation when the operational amplifier receives the analog current signal and end the timing operation when the second output signal changes. A binary data resulted from the timing operation characterizes a digital signal corresponding to the analog current signal.