Advantages of the Symmetric-on Time Modulator in Multiple-Sampled Digitally Controlled DC-DC Converters

This paper presents a comparison between different types of carriers in multi-sampled pulse width modulators (MSPWMs). In the multiple sampling approach the modulating signal is sampled N times per switching period, so that the PWM waveform is updated at a rate which is a multiple of the switching frequency. It can be shown that the increased sampling frequency leads to a significant reduction of the small- signal delay with respect to the single-sampled PWMs, allowing for higher bandwidths to be achieved in closed-loop operation. Beside these desirable effects, sampling the modulating signal causes dead bands to appear in the modulator transcharacteristic. Depending on the specific carrier waveform, these sampling-induced dead bands differently affect the PWM operation. In particular, the symmetric-on time modulation is found to be superior among other modulation schemes in terms of achievable closed-loop performances. Simulations and experimental results are provided to validate our analyses.