Ultra Wide-Band Circulator through Sequentially-Switched Delay Line with Resonant Gate Drive
This work seeks to supplement the work previously done on the Ultra-Wide Band SSDL Circulator. The technique, Sequentially-Switched Delay Line (SSDL), is applied in this circuit to achieve non-reciprocal behavior using only classical, reciprocal integrated circuit elements. Previous iterations of this project have yielded successful results; showing the ability to achieve wide band circulator performance from on-chip measurements. The control element essential to the performance of the circuit is the appropriate biasing of the gates of the Gallium-Nitride (GaN) Field Effect Transistor (FET) switches. These high-power, high-channel breakdown devices require gate bias ranges spanning 10 V to 0 V. Driving such large gate voltages causes the circuit to draw a large amount of power, on the order of watts. In this work, resonant Inductor-Capacitor (LC) sections were used at the gate drive to boost the switching signal through the resonant gain effect. The resultant work showed that a small input gate drive signal could be boosted by the LC section to the required voltages to drive the GaN FETs. On-chip measured results showed close to a ten-fold reduction in circuit power consumption with no impact on performance. Realistic implementations of this technique are fundamentally limited by the quality factor of the LC section components. Two circuits were fabricated, a 1.25 GHz variant and a 2.5 GHz variant, and are described in this work.