An analog-to-digital converter includes a plurality of sequentially cascaded stages, each stage including an amplifier and four copies of a circuit block including a flash and capacitors, in which the four copies of the circuit block operate interleavingly in a respective sample mode, pre-gain mode, gain mode, and reset mode of the circuit block, the copies of the circuit block in the sample mode, pre-gain mode, and reset mode are decoupled from the amplifier, and the copy of the circuit block in the gain mode is coupled to the amplifier to produce an output for a next following stage.