Programable gain amplifier and gain control method

A gain control method, configured to provide a gain value to an input signal to generate an output signal, comprising:

• using a capacitor array to receive the input signal, wherein the capacitor array is coupled to an input terminal of an operational amplifier and comprises a first capacitor, a second capacitor and a third capacitor arranged in parallel, wherein each of the first capacitor, the second capacitor, and the third capacitor has a first terminal and a second terminal, wherein the first terminal of each of the first capacitor, the second capacitor, and the third capacitor is configured to receive the input signal, and the second terminals of the first capacitor, the second capacitor, and the third capacitor are selectively coupled to an input terminal of the operational amplifier or a ground terminal according to a first switch, a second switch and a third switch, respectively, wherein the first capacitor, the second capacitor and the third capacitor respectively has a first capacitance, a second capacitance and a third capacitance, wherein the third capacitance equals to a sum of the first capacitance and the second capacitance;
• in a first configuration, operating the first switch and the second switch in a first conduction state, and operating the third switch in a second conduction state;
• when converting from the first configuration to a second configuration, operating the third switch in the first conduction state, and operating the first switch and the second switch in the second conduction state, wherein the gain value provided in the first configuration and the gain value provided in the second configuration are the same;
• and
• using the operational amplifier to output the output signal according to the second configuration.