Improved fully differential circuits using hybrid structures

Fully differential circuits offer improved dynamic range over their single-ended counterparts, however such circuits require additional common-mode feedback in order to define the common-mode voltages. A method for implementing fully differential circuits without common-mode feedback was presented previously by the authors; however circuits designed using this approach do not have the common-mode rejection of conventional fully differential circuits. This can result in degraded dynamic range when large common-mode signals are present. In this paper we examine a hybrid fully differential circuit, which combines both conventional fully differential circuits with common-mode feedback and fully differential blocks without common-mode feedback in order to utilize the advantages of both approaches.