Design optimization of noiseless feedback amplifier

One of the challenges in noiseless feedback amplifier (NFAs) design is to optimize the RF transformer that is required to provide proper feedback with minimum loss. Because of inherent parasitics associated with RF transformers and insufficient design guidelines, the design of NFAs and their transformers has been a difficult and time-consuming process involving trial-and-error. This paper presents detailed analysis and measurements of two different NFAs. Through CAD simulations and analysis using S-parameters, the NFAs and the RF transformers are characterized. The design parameters that affect the NFAs performance are derived and analyzed. The results of this article provide a detailed insight into the RF transformer design for noiseless feedback applications, so that the design of NFAs may be optimized, and the design cycle reduced.