A novel true logarithmic amplifier in 0.25 μm GaN-on-SiC technology for radar applications

A new circuit topology for a true logarithmic amplifier (TLA) basic cell is presented. The basic cell is synthesized in quasi-distributed form as the cascade of two single-FET stages. Whereas the operating principle of the overall TLA is well-known (i.e., cascading several hard-limiting cells), the topology of the proposed basic cell is not common. The broadband characteristics and the extreme compactness of the proposed architecture make it particularly suitable for the realization of multi-stage TLAs. The proposed basic cell is then adopted to design, as a test vehicle, a six-stages TLA, using a 0.25 μm GaN-on-SiC HEMT technology provided by UMS foundry. The final MMIC exhibits a broadband behavior, in the range 1.2 GHz-2.2 GHz, with a global logarithmic error of ±1 dB over 60 dB of input dynamic range (IDR).