A new method to improve the impedance of the CC-II´s X input

This paper presents a new method to improve the CC-II´s X input impedance. The new method applies a double feedback scheme, comprising both series-shunt negative and series-series positive feedback paths. This method achieves input impedance levels below -15 dBΩ (comparable to other reported methods), with controlled frequency peaking. Simulation results compare the frequency performance of the proposed method with other reported methods, using the same reference CC-II. The effects of feedback on current and voltage transfers of the CC-II are also discussed, pointing to limiting factors on impedance reduction.