A Low-EMI Fast-Transient-Response Buck Converter Using Delta-Sigma Modulation

This paper proposes a second-order continuoustime delta-sigma modulated buck converter to enhance electromagnetic interference (EMI) suppression and accelerate transient response. By leveraging oversampling and noise-shaping techniques from delta-sigma modulation (DSM), the proposed design effectively reshapes switching noise to high-frequency bands, thereby suppressing the EMI of the output spectrum. An enhanced transient-response loop is incorporated to improve dynamic performance. The proposed converter has been implemented using a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0.35 \mu \mathrm{m}$</tex> BCD process. The measured results indicate that the peak noise power is -59.357 dBV, and the output-to-noise ratio (ONR) is 64.46 dB at a sampling frequency of 5 MHz. Under 1.8 V output voltage conditions, the converter exhibits transient settling times of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$5.69 \mu$</tex> s (load step-up from 1 A to 5 A) and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$7.08 \mu$</tex> s (load step-down from 5A to 1A). Corresponding output voltage deviations are measured at 82.4 mV undershoot and 64 mV overshoot, respectively. The maximum output voltage ripple is 4.2 mV. Under 5A load condition at 1.8 V output, the converter achieves <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{9 1. 2 \%}$</tex> peak power conversion efficiency.