A Delta-Sigma Based Buck Converter - Design Methodology for Wireless Systems

Shoba Krishnan; Kamala Hariharan
Wireless systems customarily use LDO for excellent noise performance at the expense of poor power efficiency. Switching regulators using Pulse Width Modulation (PWM) controllers offer better efficiency but have greater magnitude spurs at multiples of the clock frequency. In this paper, a switching regulator that uses a delta sigma (ΔΣ) controller is considered as a substitute to provide both high power efficiency and improved spurious performance. Tradeoffs in selecting the ΔΣ parameters are investigated for several wireless standards such as WIFI, Bluetooth, GSM, W-CDMA, HSPA, LTE and WIMAX. Simulations in 0.5 µm CMOS technology, performed for key parameters such as spurious performance, efficiency and transient response show that the ΔΣ controller having 3rd order and over sampling ratio (OSR) of 32 can meet the stringent spectral conditions of a GSM system by a 10 dB margin. It also has 8% better power efficiency compared to the PWM controller. The performance of using this ΔΣ buck regulator for dynamically changing load applications is also analyzed. It is shown that for a 13% change in output voltage VOUT, the ΔΣ buck regulator can still meet the spurious constraints of the GSM system.
Buck Converter; Delta Sigma Controller; PWM Controller; Wireless Applications; Wireless Standards; Noise Performance; Noise Shaping; Transient Performance; Envelope Tracking
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