Novel cross-connected cascode differential amplifier

We report on a novel amplifier circuit-differential cross-connected cascode1. Its fundamental distinction from an ordinary differential cascode lies in simultaneous feeding of input signal both to the common emitter (source) and common base (gate) stages, which are cross-connected. Such a connection results in the creation of two loops of positive current feedback. The stability of the amplifier is achieved due to low gain and phase shift in the loops. We show that the input signal is amplified in the input circuit. The input and output impedances are gained significantly as well. The current gain is increased considerably and the bandwidth is essentially expanded. Simulation results of such a cascode designed with IBM BJT sige5am and CMOS bicmos7hp transistors are presented. When compared with the ordinary cascode, the predicted and actually obtained bandwidths proved to be more than twice as wide: 8.6-18.7 GHz and 3.4-8.7 GHz on BJT and CMOS based, respectively.