Passive phase shifters and their applications in RF front-end circuits

This paper describes a recently developed two-port chip-component which provides a specified phase shift at a given frequency for an RF signal as it passes between the ports of the component. This chip phase shifter has a range of potential applications in RF front-end circuits for cellular and wireless devices, such as optimising the output power of the PA, and improving the linearity of the RF front-end circuit. Experimental results demonstrating the importance of phase matching within RF front-end circuits for GSM and UMTS are presented and discussed. The chip phase shifters are fabricated in multi-layer LTCC, where the chip has outer dimensions of 1.0 times 0.5 times 0.5 mm³. A first generation line-up of chip phase shifters has been developed and mass production has already commenced. A range of positive and negative phase shifts are available, where the phase shift is nominally specified at the centre frequency of one of the cellular GSM bands.