Effect of supply scaling on noise performance of 0.6–1.2 V continuous‐time delta‐sigma modulator

Abstract

The dependence of the noise performance of a 0.6–1.2 V continuous‐time delta‐sigma modulator (DSM) on its supply voltage is analysed. The noise performance and benchmark figure of merit (FoM) mainly depend on the power dissipation, thermal noise contributions from the analogue loop filter, and the quantisation noise from the quantisers. Theoretical estimates for the supply dependence of loop noise and quantisation noise, and their respective FoM are derived and verified with simulations for a 2 MHz third‐order continuous‐time DSM, while operating from a supply between 0.6 and 1.2 V. At a larger supply voltage, the FoM related to the loop filter noise improves, whereas at lower supplies, the FoM related to the quantisation noise improves. As a result, the overall FoM of the DSM reaches an optimum at a particular supply. The supply voltage with the best FoM of the DSM is derived with the supply‐scaling FoM of the loop filter and quantisers. For an equal FoM of the loop filter and quantisers at a supply VDD,0, the optimal supply voltage is 0.66 VDD,0.

Keywords

• loop filter noise
• quantisation noise
• supply‐scaling FoM
• quantisers
• equal FoM
• optimal supply voltage