Small-signal analysis of fully-differential closed-loop op-amp circuits with arbitrary external impedance elements

An analytical modelling approach for fully differential amplifiers is presented and validated through examples. Separation of the analysis into two steps coupled with linear superposition techniques leads to concise mathematical expressions. An added benefit of the two-step approach is that the usual symmetry assumptions are not needed. As a consequence, the results hold for arbitrary element values. The mathematical results are validated by comparison to SPICE simulations and experimental data.