Optimal dithered digital sigma-delta modulators for fractional-N frequency synthesizers

By using a structured dither addition it is demonstrated how a very simple 8-bit linear feedback shift register (LFSR) can be used to randomize a digital MASH 1-1-1 SigmaDelta modulator used for fractional-N frequency synthesizers. With this optimization, spur tones for high frequency offset from the carrier are avoided without significant area and power budget increase.