A New Improved $2^{nd}$-Order Delta-Sigma-Modulation Buck Converter with Low-Noise and Transient- Acceleration Loops

This paper proposed a new improved fasttransient-response and low-noise high-efficiency buck converter with second-order continuous-time delta-sigmamodulation (CT-DSM) techniques. First, by utilizing the oversampling theorem and noise-shaping technique with the second-order delta-sigma modulator, the output noise within the bandwidth can be reduced effectively. Second, the adding of transient acceleration loop can not only improve the transient recovery time when the load current changed, but also lowers the undershoot and overshoot voltage. Third, a rail-to-rail operational transconductance amplifier without voltage dividers is employed in the proposed converter, which helps sensing the inductor current, moving the inductor pole to high frequency, speeding up the transient response, and stabilizing the proposed converter modules. Last, the proposed converter has been implemented with TSMC 0.18μm 1P6M process and occupies an area of $1.19 \times 1.19 {\tex t{mm}}^{2}$ . When the load current changed from 50 to 500 mA and 500 to 50 mA, the transient recovery time were both 4 μs, which improved 8 μs and 16 μs than the traditional CT-DSM converter. The output voltage ripples are kept under 13 mV and the overshoot and undershoot voltage are 20 mV and 14 mV, respectively. The measured output-to-noise ratio (ONR) is 80.7 dB, with the sampling frequency of 10 MHz. The peak efficiency is 92.1%, at the output voltage of 2.5 V and load current of 150 mA.