Transformer-Feedback Dual-Band Neutralization Technique

A dual-band neutralization technique based on the transformer feedback between the drain and the gate of a transistor is presented. The drain and gate bias lines of the transistor are realized as multiorder LC networks. Transformer coupling between the inductors of the two networks can be used to concurrently neutralize the gate-drain capacitance of the transistor at multiple frequencies. Moreover, these frequencies can be placed close together to achieve wideband neutralization. A proof-of-concept dual-band 27/33-GHz amplifier is designed and implemented in a 0.1-mu m GaAs pseudomorphic high-electron mobility transistor process. The maximum gain of the transistor at the two frequency bands is improved by more than 6 dB using the neutralization technique. The amplifier exhibits a gain of 16/15 dB and a reverse isolation of 60/50 dB at the lower/upper frequency band. It consumes 24 mA from a 1-V supply.