Intermodulation-distortion performance of silicon-carbide Schottky-barrier RF mixer diodes

This paper presents the fabrication and characterization of silicon carbide (SiC) Schottky-barrier mixer diodes of 25- and 50-/spl mu/m diameter on a conducting 4H-SiC wafer. The single-balanced mixer circuits with a diode in each arm (two diodes total) were tested at 200 MHz (VHF) and 1.5 GHz [global positioning system (GPS)]. The experiments show that the conversion loss/input third-order intercept point (IP3) are 8.0 dB/+25 dBm and 7.5 dB/+22 dBm at these frequencies, respectively. The measured second-order intercept point (IP2) over the VHF frequency band is +38 dBm. The above conversion-loss values are about the same as that of commercially available single-balanced mixers with silicon Schottky-barrier diodes. However, to achieve a comparable input IP3 performance with Si Schottky-barrier diodes, a more complex mixer design involving double-balanced mixers with two diodes in each arm of a quad (eight diodes total) is required. Applications include RF-based navigational instruments on board commercial/general aviation aircraft and GPSs.

I. Introduction

Electromagnetic (EM) emissions from carry-on electronic devices can potentially degrade the minimum detectable signal level of important RF-based navigational instruments on board commercial and general aviation aircraft [1]–[3]. In some situations, the interfering signal frequencies may not coincide, but may be very close to the navigational instruments operating frequencies. For example, the lowest frequencies used for VHF omni-directional range (VOR) and instrument landing system (ILS) localizer instruments are just above commercial FM broadcast frequencies. In such cases, the intermodulation distortion (IMD) products are located adjacent to the desired signal spectrum at the output. The IMD products are generated because of nonlinear circuits, such as mixers, within the instruments.