CMOS RF power amplifier with a switchable transformer

Abstract

It is found that if we want to design power amplifier for EDGE polar transmitter without feedback, we need dynamic range enhanced power amplifier. Additionally, if we can increase minimum supply voltage with dynamic range enhanced power amplifier, we can also reduce spurious output generated from DC-DC converter ripple voltage. If DC-DC converter can be used instead of LDO, the efficiency of transmitter can be greatly improved. Current power amplifier is composed of many different materials. Near future, it will converge to single chip CMOS IC. For better performance, shorter gate length process is preferred for CMOS power amplifier design. CMOS power transistor characteristics are mainly from interconnection effect. Interconnection inductance makes lower the power amplifier input impedance which makes the input matching difficult. The thermal effect is not dominant for CMOS power transistor. So, even if we don’t measure and model power transistor, we can predict power transistor characteristics with EM(electro-magnetic) simulation. The optimum power transistor size for high efficiency is decided by the turn-on resistance and required input power. These two parameters have trade off relation and the optimum value for efficiency changes according to the operating frequency. The transformer ratio switching to change the power amplifier load impedance can increase the dynamic range and average power efficiency. Additionally, the cascade structure of the power amplifier endured high breakdown voltage also increased the dynamic range. To save the chip area, the power transistors was located inside the transformer without degrading the performance. The optimum transformer parameter such as width and inductance was solved analytically with the suggested transformer model. In the high-power mode, when the operating frequency was 2.1 GHz and the supply voltage was 3.0 V, as in fig. 4.5.1, the saturated output power of the power amplifier was 30.7 dBm, the maxi...