Low dropout (LDO) voltage regulator design using split-length compensation

Abstract

We explore the application of split-length compensation to the design of a three-stage low dropout (LDO) voltage regulator. Initially, we review three basic compensation techniques, Miller, cascode, and split-length, and demonstrate their use in a multi-stage amplifier. It is found that stable designs are possible using single Miller compensation, whereas both cascode and split-length compensation require a Miller compensation network in parallel. Finally, we compare the three compensation techniques in terms of quiescent current, area, dropout voltage, unity-gain frequency, line and load transient response, and power supply rejection. For the LDO architecture selected, it is found that cascode and split-length compensation offer very similar performance, with the exception of quiescent current and area. Cascode compensation required 24% less total compensation capacitance, whereas split-length compensation used 14% less quiescent current.