Simplifying the Design of ΣΔModulators Using FGMOS Transistors
This paper presents the novel design of a second-order continuous-time low-power and low-voltage SigmaDelta modulator. The modulator illustrates a design philosophy based on taking advantage of the extended number of degrees of freedom of the floating-gate MOS transistor. The transistor is simultaneously used to fulfill the following: simplify the topology; accurately implement the modulator coefficients; compensate for gain losses in the integrator and several nonidealities in the comparator; increase the signal range; reduce distortion; shift signal levels according to the specific requirements of individual devices; implement an easy common-mode sensing and feedback strategy; and tune the loop filter and reset the comparator. The modulator operates at 1 V and consumes just over 5 muW of power for a signal-to-noise-and-distortion ratio of 60 dB and a maximum bandwidth of 2 kHz, which are typical of many biomedical applications.