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Randomized Modulation for Low-Harmonics Low-Noise Switched-Mode DC-DC Converters


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The The global market for low-power portable electronic devices is gargantuan and rapidly growing. For examples, the market for tablets and smartphones is estimated to reach more than 2.3 billions of devices by 2018, and for Internet-of-Things (IoTs) is estimated to reach more than 20 billions of devices by 2020. These devices are becoming more intelligent due to an increasing array of mixed-signal ICs, System-on-Chips, and sensors employed therein. This means more DC-DC converters are needed to convert the battery voltage into different voltages for the various circuits and sensors. Due the limited PCB area and the small physical size constraints, it is imperative that these converters employ external passive components that are as small as possible. Among the different converters, switched-mode DC-DC converters are widely used due to their high power-efficiencies. However, conventional switched-mode DC-DC converters based on the Pulse Width Modulation scheme (PWM) are inherently noisy, and generates strong harmonics at multiples of the switching-frequency in the input current and the output voltage spectra. The harmonics at the input current can cause conducted electromagnetic interference (EMI) noise that travels along power lines or PCB traces, and causes interference to other electronic circuits near the converter. Mitigating the harmonics can be done using larger passive filters, but this is undesirable due to the area and size constraints in portable devices. In this seminar, we present a novel randomized modulation scheme that mitigates the switching-frequency harmonics without the need to use large passive filters. We subsequently present our proposed hybrid scheme that combines the randomized modulation with a noise-shaper to further attenuate the low-frequency noise in the frequency spectrum. We also present a novel pulse generator structure that translates the duty cycle input into output pulses of the hybrid scheme, and show the computer simulations of a switched-mode DC-DC converter embodying the pulse generator.