Delta-sigma buck converter — A design exploration for GSM Wireless systems

Global Systems for Mobile communications (GSM) traditionally use linear drop out regulators (LDO) to power the different components of the system. LDOs have excellent noise performance and low power efficiency while switching regulators offer higher efficiency but have large spurs occurring at integer multiples of the clock frequency. In this work, a switching regulator that has a delta sigma (ΔΣ) controller is considered as an alternative to provide both power efficiency and better spurious performance. Tradeoffs in selecting the ΔΣ order and over sampling ratio (OSR) for different input voltage (V_in) range are investigated for GSM wireless application. While a large OSR can reduce the magnitude of the spurs and push them out to a higher frequency, the power efficiency of the system is compromised:Using a higher order gives better spurious performance, allowing the designer to select a lower OSR at the expense of increased complexity. This paper aids designers in investigating the design space for the optimal ΔΣ parameters given efficiency and spurious performance specifications. It is shown that a 3rd order ΔΣ controller with OSR of 32 can meet the spectral requirements for a GSM system by a 16dB margin.