An Active Bandpass Filter for LTE/WLAN Applications Using Robust Active Inductors in Gallium Nitride

Abstract

This brief demonstrates the performance of the first active bandpass filter to implement an active inductor in gallium nitride (GaN) technology. Fabrication of the filter and inductor was done using a 0.5 μm pHEMT GaN process with the system implemented on one 2 mm by 2 mm die. The tuning range of the active filter was measured to be 749 MHz at a centre frequency of 3.39 GHz with separate amplitude and quality factor tuning. An amplitude range for S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> was measured to be from -12.2 dB to 13.7 dB within the operating frequency range. Taking advantage of the active inductor's negative impedance the filter was able to produce a quality factor of 138. On-chip, the active inductor occupies an area of 350 μm by 175 μm compared to approximately 350 μm by 350 μm for their passive counterparts of similar inductance (a 50% decrease in size). The filter was designed for LTE/WLAN applications to demonstrate the capabilities of the active inductor.