Characterization of Si-based monolithic transformers with patterned ground shield

This paper investigates the impact of patterned ground shield on monolithic integrated transformers. The minimum insertion loss is shown to be a useful figure of merit. It is used to evaluate transformer performances. We demonstrate that the use of a patterned ground shield increases the quality factor of both primary and secondary coils. It increases also the mutual coupling coefficient and thus reduces the minimum insertion loss at high frequency, while at low frequency it has no effect. Measured insertion loss as low as 1.27dB at 5GHz, has been observed. The impact of patterned ground shield is shown to be more significant in the case of transformer with important transformation ratio.