10MHz current mode 4 switch buck boost converter (4SBBC) for polar modulation

This paper presents a transistor level design of a current mode 4 switch buck boost converter (4SBBC) for polar modulation. The reference signal of this 4SBBC is the envelope signal of EDGE (Enhancement Data-rate for GSM Evolution) standard which has more than 200 kHz bandwidth. In order for output voltage to follow this fast varying reference signal, this 4SBBC uses current mode control with 10 MHz fixed switching frequency which demands high bandwidth circuit design. This paper will show how to design the high speed current sensor and oscillator well operating with 10 MHz switching frequency. The current sensor exhibits rail to rail input and output range, and active feed back scheme makes it work well in 10 MHz switching frequency range. The oscillator generates 2 sawtooth signals which have precise and stable 180 degree phase shift each other by using common mode feedback scheme. The transistor level simulation shows this 4SBBC converter has more than 80% average efficiency with real EDGE envelope reference and is capable of wide input, output voltage range which is suitable for EDGE polar modulation.