New small-signal macromodel for current-feedback op-amps

Current feedback operational amplifiers (CFOA) are now recognised for their excellent performance in high speed and high slew-rate analog signal processing applications. Simple circuit level macromodels of the conventional voltage op-amp (VOA) are useful in analysis and give the applications engineer valuable insight into the operation of the VOA, and the same is true for the CFOA. Semiconductor manufacturers' macromodels for the CFOA enable application circuit performance predictions to be made rapidly, but they are generally too complex to provide insight into the operation of the device. The almost universal 'standard' CFOA simple circuit level small-signal macromodel does enable closed-loop gain predictions to be made. However, it is over simplified and cannot be used to predict closed-loop input and output impedance levels with any accuracy, nor the effects of load impedance on the performance of the CFOA. In this paper a new simplified small-signal macromodel is introduced which models the input and output common-collector buffer stages of the CFOA as a composite BJT and is shown to give improved insight into the small-signal operation of the CFOA.<>