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This paper presents a novel approach to achieve a high Q series negative capacitor (NC). A stepped-impedance distributed amplifier (DA) is used to achieve the negative group delay (NGD) response. The input/output (I/O) impedance of the transistor in each stage is calculated to meet the specific voltage gain coefficient ratio. By this way, the NGD phenomenon can be observed between the input and reversed output ports of DA. A major advantage of this architecture is that the gain is configurable while maintaining a fixed NGD. By properly choosing the gain coefficient, the proposed circuit can exhibit the same S 21 as an ideal NC network. From the experimental results, it can be calculated that in 1.4-1.55 GHz the NGD circuit can exhibit the desired equivalent NC value. In addition, thanks to the active structure, the circuit shows a high quality-factor (Q) performance.

In this paper, a scalable large signal GaN HEMT model including nonlinear thermal sub-circuit is described. Only two scalable parameters are needed in the I ds scalable model by introducing a simple correction factor. The established model can predict the I-V curves at different-in-size AlGaN/GaN HEMTs devices accurately. Small signal S-parameters and large signal load pull tests with on-wafer measurement is used to further validate the proposed model. Finally, the proposed scalable model is used to design a broadband high efficiency continuous class-E power amplifier (PA). Experimental results show that this class E PA is realized from 2.5-3.5 GHz with drain efficiency of 60%-70%, over 8.2 dB gain and over 35.2 dBm output by using a GaN HEMT with 1.25 mm total gate width. The results show that the proposed model is useful for high efficiency amplifier design.

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