Various bioFET sensor readout circuits and their methods of operation are described. A readout circuit includes a plurality of logic gates coupled in cascade, a delay extractor, and a counting module. Each logic gate of the plurality of logic gates includes at least one bioFET sensor. The delay extractor is designed to generate a pulse-width signal based on a time difference between an output signal from the plurality of logic gates and a reference signal. The counting module is designed to receive the pulse-width signal and output a digital count corresponding to a width of the pulse-width signal.