A Dual-Mode Continuous–Time Sigma-Delta Modulator With a Reconfigurable Loop Filter Based on a Single Op-Amp Resonator

This brief proposes a dual-mode continuous-time (CT) sigma-delta modulator (SDM) for switched-mode power supplies comprising a switchable loop filter (LF) based on a single op-amp resonator (SOR). The proposed modulator adaptively adjusts the LF architecture between the third and second order and optimizes the noise transfer function (NTF) using the partial resistors as per the sampling frequency. This facilitates the desired bandwidth and resolution while mitigating design complexity and minimizing the need for tuning circuitry. Moreover, the LF implemented with the SOR enhances both the power and area efficiency of the modulator in each operating mode by reducing the number of active components. The modulator was fabricated based on an 0.18- $\mu $ m CMOS process with an active area of 0.105 mm2. It achieved peak signal-to-noise ratios (SNRs) of 66.0/65.3 dB for signal bandwidths of 0.5/1.1 MHz. The power consumptions were 127/ $280~\mu $ W from a 1.8-V supply when clocked at 40/160 MHz. The figures of merit for each mode were 82/93 fJ/conv.-step.