Dithered multi-bit sigma-delta modulator based DPWM for DC-DC converters

Multi-bit sigma-delta based digital pulse width modulators (DPWM) are used in the control of DC-DC converters in order to achieve high resolution and therefore high output voltage accuracy at switching frequencies up to multiple MHz. The standard sigma-delta modulators which have mainly been used in these DPWMs to date generate idle tones in the applied duty cycle which result in large oscillations in the output voltage. A dithered sigma-delta modulator is instead implemented here which eliminates these oscillations in the output voltage by adding a random signal before the quantizer in the sigma-delta modulator. The power spectral density of the duty cycle produced by the dithered sigma-delta modulator based DPWM shows a reduction in the undesirable idle tones and this is also verified experimentally using a buck converter prototype.