A Fully-Balanced Operational Amplifier

A method for analysis and design of Fully-Differential (F-D) analog circuits is presented. It is based on defining a Fully-Balanced Operational Amplifier (FBOA), which works with balanced signals; this is with common mode and differential mode voltages as a whole, allowing analysis and design of both operational modes behaviors. The FBOA can be implemented as a monolithic circuit but it can also be easily built using standard single-ended (S-E) operational amplifiers. This structure can be found in many typical F-D feedback circuits, providing a new framework for their analysis. The proposed device also provides a simple way to design F-D circuits and allows the implementation of inverter and non-inverter F-D topologies. Typical application circuits are analyzed and, as a design example, a "double-mode oscillator (a circuit that has independent common mode and differential mode oscillations) is presented. Experimental tests performed on this circuit validate the proposed technique.