EMC influence of the charge pump in linear regulators - Design, simulation and measurements

The charge pump belongs to the most critical blocks for electromagnetic compatibility (EMC) of low dropout linear regulators (LDO) because of its switching nature. The goal of this paper is to contribute charge pump design practice and a prediction method for the LDO EMC performance already in an early design phase. LDO noise coupling mechanisms are analyzed. EMC aware circuit design includes the choice of low noise architectures, the right switching frequency and noise filtering. The derived simulation method shows very good matching with EMC test results for an LDO with two different charge pumps fabricated in 350nm high-voltage BiCMOS technology. For a realistic prediction of the EMC noise magnitude, a relatively simple simulation setup gives results with <;3dBμV accuracy. A trippler current mode charge pump turned out to be well suitable for EMC. Conducted emissions could be predicted and confirmed to be improved by ~50dBμV versus a conventional voltage mode charge pump.