Reconfigurable CMOS Tuners for Software-Defined Radio

A reconfigurable tuner is demonstrated by using a low-loss shielded coplanar waveguide transmission line periodically loaded with CMOS transistor switches in series with capacitors. The switch-capacitor combination is used to change the local impedance of the transmission line in a binary fashion. It achieves a higher capacitance ratio (by 60%), less transmission loss (by 40%), higher quality factor (by 100%), and subsequently wider bandwidth and better Smith impedance chart coverage compared to optimized CMOS varactors realized in the same technology. The 5-16 GHz tuner demonstrated here is implemented in a standard 0.13-mum CMOS technology and can be configured to 2²⁰ different impedances through an integrated 20-bit shift register.