A signal processing circuit including a plurality of analog-to-digital conversion circuits, an in-memory computing device, and a control method thereof are provided. Each analog-to-digital conversion circuit includes a reset switch, a capacitor array circuit, a voltage comparator, and a successive approximation circuit. A first terminal of the reset switch receives a first reference voltage, and a second terminal of the reset switch receives an input voltage signal. The capacitor array circuit adjusts the input voltage signal according to a successive approximation control signal to generate an adjusted voltage. The voltage comparator compares the voltage levels of the adjusted voltage and a second reference voltage to generate a comparison signal. The successive approximation circuit generates a successive approximation control signal according to the comparison signal and generates an output digital signal corresponding to the input voltage signal. The capacitor array circuit maintains the input voltage signal during a non-reset stage.