CMOS射频功率放大器中的变压器合成技术

Transformer Power Combining in CMOS RF Power Amplifier

设计了一种可在CMOS射频功率放大器中用于功率合成的宽带变压器。通过对变压器的并联和串联两种功率合成形式进行分析与比较,指出了匝数比、功率单元数目以及寄生电阻对变压器功率合成性能的影响;提出了一种片上变压器的设计方法,即采用多层金属叠层并联以及将功放单元内置于变压器线圈中的方式,解决了在CMOS工艺中设计变压器时面临的寄生电阻过大及有效耦合长度不足等困难。设计的变压器在2～3 GHz频段内的损耗小于1.35 dB,其功率合成效率高达76%以上,适合多模多频段射频前端的应用。

A wide-band transformer for power combining in CMOS RF power amplifier was designed. Two types of transformers, serial and parallel combining, were analyzed and compared, It has been demonstrated that turn ratio, number of primary windings and parasitic resistor are key factors for power combining performance. By paralleling stacks of multi-layer metal and locating the power cell in windings, an on-chip transformer was designed to overcome large parasitic resistance and insufficient coupling length. The transformer features a maximum loss of 1. 35 dB in the frequency band range from 2 GHz to 3 GHz and a power combining efficiency above 76%.