Comparison of two SiGe 2-stage E-band power amplifier architectures

This paper presents simulation and measurement results for two 2-stage E-band power amplifiers implemented in 0.18 μm SiGe technology with fr = 200 GHz. To increase the power gain by mitigating the effect of the base-collector capacitance, the first design uses a differential cascode topology with a 2.7 V supply voltage. The second design instead uses capacitive cross-coupling of a differential common emitter stage, previously not demonstrated in mm-wave SiGe PAs, and has a supply voltage of only 1.5 V. Low supply voltage is advantageous since a common supply can then be shared between the transceiver and the PA. To maximize the power gain and robustness, both designs use a transformer based interstage matching. The cascode design achieves a measured power gain, S21, of 16 dB at 92 GHz with 17 GHz 3-dB bandwidth, and a simulated saturated output power, Psat, of 17 dBm with a 16% peak PAE. The cross-coupled design achieves a measured S21 of 10 dB at 93 GHz with 16 GHz 3-dB bandwidth, and a simulated Psat, of 15 dBm with 16% peak PAE. Comparing the measured and simulated results for the two amplifier architectures, the cascode topology is more robust, while the cross-coupled topology would benefit from a programmable cross-coupling capacitance.