A readout system used for generating an output code associated with an environmental parameter and comprising a sensing module and a readout module is provided. The readout module includes a first delay lock loop and a readout circuit. The sensing module generates two signals according to the environmental parameter and an input voltage signal. The positive edges of the two signals have a first time difference associated with the environmental parameter value. The first delay lock loop delays the leader of the two signals by a correction time associated with a predetermined environmental parameter value to produce the other two signals. The readout circuit converts a second time difference between the positive edges of the other two signals into the output code. By delaying the correction time, the same output code can be obtained even if each readout system has a different first time difference for the same environmental parameter value due to the process.