A Cross-Coupled CMOS Negative Capacitor for Wideband Metamaterial Applications

Non-Foster circuits can be used to provide broad-band impedance matching for antennas and metamaterials. These circuits allow effective matching over a much wider bandwidth than is expected from traditional passive components. Therefore, this paper considers the design and test of a negative capacitor in a 0.5 micron CMOS process. The proposed circuit uses a cross-coupled design to allow for floating operation, and the design's simulated performance works well at high frequency. Measured results show a low-frequency capacitance of -1.7 pF and within 10% to 200 MHz, and falling to -4 pF at 230 MHz. Although the selected CMOS process is adequate to demonstrate the basic design approach, more advanced process nodes would be expected to extend performance to even higher frequencies. Results are also presented showing performance of the circuit in a metamaterial.