Power conversion techniques for portable EMI sensitive applications

In circuit applications that demand low noise, such as in many portable wireless devices, there is a need to optimize circuit design in power converter circuits. The path to low noise performance does not necessarily require exotic circuit techniques or the latest IC features. Conventional low noise power supply techniques are “tweaked” to improve the performance of DC/DC conversion circuits. A series of improved circuit designs are outlined such as redesigns in push-pull converters, the use of negative railing, the usage of charge pumps (also known as inductorless design), single resistance-capacitance filter, and PCB ground layout. The design techniques are explained and sample circuits are shown. Noise measurements of such re-designed circuits are performed with the improved results explained. Some final attention is paid to pitfalls occurring from using digital layout design hardware in the use of mostly analog layout methods in power conversion circuits