Pros and Cons of Design Choices on Analog and Digital LDOs
Research Report Highlight
TxACE researchers at GaTech assess the tradeoffs for a series of voltage regulators, covering all-digital LDOs, switched mode hybrid LDOs, and unified voltage and frequency regulator.
All digital LDOs are designed with synchronous digital control that enables sampling of the output voltage followed by comparison and thermometer based output power PMOS actuation. The strength of the design lies in its simplicity and process and voltage scalability. We have demonstrated 0.5V dropout at NTV with less than 1us droop recovery time. However the biggest challenge with this design is the low small signal gain and existence of output ripple. We have developed models of the limit cycle ripples as well as ways to mitigate them. However, the all digital designs are limited by the small signal gain and hence suffer from low PSR.