Switchable Resonator Enhances SPDT Switch Design

Single-pole double-throw (SPDT) switches that operate beyond 140 GHz are often implemented with an impedance-inverting transmission-line topology. But this topology can result in high insertion loss, which has been problematic in millimeter-wave and terahertz SPDT switch designs based on CMOS and biCMOS technologies. However, incorporating a switchable resonator into switch designs can help improve performance. For instance, a group of researchers from China and Singapore utilized the switchable resonator technique to develop an SPDT switch that operates from 220 to 285 GHz.

The proposed SPDT switch was designed using a 65-nm bulk CMOS process. It comprises three coupled-lines, two transistors, a compensating capacitor, and two biasing resistors located at the transistor gate terminals. ANSYS’s High Frequency Structure Simulator (HFSS) software was used to optimize the design parameters.

Two-port S-parameters were measured from 220 to 320 GHz. The switch’s minimum insertion loss was 4.2 dB at 250 GHz, which agreed with the simulation results. An isolation of approximately 18 dB was achieved, which also corresponded with the simulation. In addition, measured return loss was greater than 10 dB from 220 to 300 GHz. See “A 220-285 GHz SPDT Switch in 65-nm CMOS Using Switchable Resonator Concept,” IEEE Transactions on Terahertz Science and Technology, July 2015, p. 649.

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