Impedance-Oriented Approach for Maximizing Linearity in p-i-n-Diode-Based Phase Shifters

Abstract

In full-duplex telecommunication systems, where simultaneous transmission and reception occur, component nonlinearity imposes strict limits on maximum transmit power. Phase shifters, essential in phased array antennas, often contribute significantly to intermodulation distortion. In this article, an analytical approach is presented for enhancing the linearity of p-i-n diode-based radio frequency (RF) switches in phase shifters by optimizing the impedance seen by p-i-n diodes. An optimal impedance range for each p-i-n diode is identified through theoretical analysis, demonstrating improvements in linearity, as quantified by the third input intercept point (IIP3). Moreover, linearity is shown to increase when p-i-n diodes are arranged in parallel, reducing RF current in the on state, though trade-offs are acknowledged in the off state. To validate these findings, three RF switches with one, two, and four parallel p-i-n diodes, respectively, were designed and implemented using coupler impedance transformers for optimal impedance conversion. It is shown that a highly linear three-bit phase shifter with an IIP3 of 90 dBm and an insertion loss (IL) of 1.4 dB/bit was successfully designed and implemented for a frequency range of 1.9–2.2 GHz, demonstrating the effectiveness of the proposed approach. Compared to conventional p-i-n diode-based switched-line phase shifters, the design achieves an IIP3 improvement of more than 17 dB.