Greater Than the Sum of Its Parts

Most RF systems are based on a self-design approach, in which the components are con-ceived independently from one another, based on budget specifications and following a pre-assigned common 50-Ω impedance interface. This approach requires the design of separate components with their own shielding package, related size constraints, and 50-Ω terminals. When these components are then combined on the system assembling, they require many interconnecting matching and transition circuits.

Why Use Differential Components in Codesign??

Two fundamental types of microwave components may be distinguished in terms of the symmetry of the signal waveforms they support: unbalanced components (always asymmetric structures), which have one conductor with an RF voltage and the other one connected to a physical ground, and balanced components (generally symmetric structures), whose two conductors exhibit opposite signal polarities and a virtual ground (ground due to symmetry). Although they do not have a physical ground, balanced components generally have a floating (unconnected) conductor (for example, substrate's back conductor in the case of a coplanar strip-line structure), which is used as a ground in the mixed-scattering-parameter characterization procedure that will be presented later. When combined in subsystems, balanced and unbalanced components lead to differential and single-ended architectures, respectively. For balanced components, we will use the terms balanced and differential as synonyms following traditional use, depending on the context.