Synthetic Transmission Lines in Cutoff Operation for Wideband High-Impedance DC Supplies

This brief describes a novel technique for the distribution of dc power based on synthetic transmission lines with a low cutoff frequency. Since after the cutoff the impedance of these lines approaches that of an open, these components are well suited to feed dc power in circuit nodes where high impedance values are required. Narrowband bias networks based on inductors or lambda-quarter (λ/4) stubs can be substituted by the presented wideband design solution. To experimentally validate the approach, two prototypes have been implemented in a 130 nm SiGe technology. The first prototype is a synthetic line with a cutoff frequency of 12 GHz, while the second design is a distributed amplifier (DA) where a synthetic line in cutoff feeds the voltage supply. Compared to traditional approaches based on inductors or λ/4 stubs, the presented technique improves the DA bandwidth by 50% and the flatness of the frequency response. Compared to biasing achieved via the DA termination resistor, the power-added-efficiency (PAE) is doubled. To the best knowledge of the authors, this is a novel general technique for feeding dc power to any circuit from a wideband high-impedance.