CMOS Implementation of an Order Switchable ΣΔ Modulator

Although sigma-delta concepts existed since the middle of the century, only recent advances in VLSI technologies have made possible the appropriate handling of the bit stream generated by the 1-bit ADC. The spread spectrum nature of this noise shaping modulator suppresses the error in the baseband, thus improving dynamic range in the band of interest, independent of signal frequency. Paper presents a CMOS circuit design of second order sigma delta modulator with an option of selecting the order. Comparative study of first and second order sigma delta modulators is performed and best value of OSR is selected. The circuit is simulated in HSPICE 180nm level49 library. Analysis of the noise and power results of the first and second order ΣΔ modulator leads to the design of an order switchable sigma delta modulator, which is based on the resolution of ADC.