The signal to noise vatio (SNR) of conventional sigma delta analog to digital converter (ΣΔADC) reduces with input signal strength. The existing concept of adaptive quantization is applied to the design of ΣΔADC to improve SNR with high dynamic range. An adaptive algorithm and its circuit implementation is proposed. Because of the error due to the circuit implementation,an error self-calibration circuit is also designed. Simulation results indicate that SNR can be nearly independent of the signal strength.