Bandwidth limitations in current mode and voltage mode integrated feedback amplifiers

The bandwidth relations of feedback amplifiers have been the subject of intense interest in recent years. Many current mode devices such as current feedback amplifiers have appeared which seem to break what has been considered almost a fundamental law that the product of closed loop gain and closed loop bandwidth remains constant for a feedback amplifier. The constant-bandwidth relations of such amplifier designs are reviewed in this paper and they are combined with the constraints imposed by technology when the feedback amplifier is to be designed in an integrated technology. From this analysis it is concluded that although very high performance designs are indeed feasible with the constant-bandwidth configurations, there are no constant-bandwidth configurations which provide a higher potential loop gain and closed loop bandwidth than the constant gain-bandwidth product configurations