Q-Enhanced LC Resonators for Monolithic, Low-Loss Filters in Gallium Arsenide Technology

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Virginia Tech

The rapid development of wireless applications has created a demand for low-cost, compact, low-power hardware solutions. This demand has driven efforts to realize fully integrated, "single-chip" systems. While substantial progress had been made in the integration of many RF and baseband processing elements through the development of new technologies and refinements of existing technologies, progress in the area of fully monolithic filters has been limited due to the losses (low Qs) associated with integrated passive elements in standard IC processes.

The work in this thesis focuses on the development low-loss, Q-enhanced LC filters in GaAs E/D-SAGFET technology. This thesis presents a methodology for designing Q-enhanced LC resonators and low-loss, monolithic LC filters based on these resonators.

The first phase of this work focused on the Q-enhancement of LC resonator structures using FET-based active negative resistance circuits. Three passive resonators were designed, fabricated, and measured to determine their loss and frequency response. Furthermore, six Q-enhanced resonators were designed, fabricated, and measured to compare the performance of various negative resistance circuit designs.

In the second phase of this work, four of these Q-enhanced resonator designs were used to implement fully-integrated second-order Butterworth bandpass filters. Each filter was designed for a 60 MHz, -3 dB bandwidth centered at 1.88 GHz, corresponding to the North American PCS transmit band. The best filter design achieves 0 dB of passband insertion loss while consuming 16 mA of current from a 3 V source (48 mW). Passband gain (up to 15 dB) can be achieved with increased bias current before instability is encountered. The filter provides more than 30 dB of rejection at 1.7 and 2 GHz and more than 70 dB of rejection below 1.5 GHz. In the filter passband, the noise figure is 12 dB and the output 1 dB compression point is -18 dBm. These Q-enhanced LC filters have potential application as image-reject filters in GaAs integrated transceiver designs.

Q-Enhancement, GaAs, Filter, Resonators, Negative Resistance, Integrated Circuit, RFIC