Tham khảo tài liệu 'advanced microwave circuits and systems part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 64 Advanced Microwave Circuits and Systems Fig. 4. The Dynamic Feedback Small Signal Model. --------o LNA Output With ia - c2 Cgd3 s 1 . R r 3 I r 3 Z . c2 s gm3 . z RXSCGD3 s And C2 c Cgs 3 z lS r -1- CSB3 7 8 Accordingly both the impedance z and the coupling capacitor C are introduced for the LNA gain conversion optimization. On the other part the dynamic feedback based on a source follower circuit with an inductive output allows an inductive behaviour of the feedback circuit input impedance Fig. 5 witch helps improving the small signal gain too with more idealized voltage-voltage amplifier circuit Razavi 2001 . Consequently the dynamic feedback circuit can also make it possible to minimize the NF induced by the purely capacitive feedback circuit proposed by Cusmai Brandolini 2006 . Fig. 5. The Dynamic Feedback Input Impedance. 65 Multi-Block CMOS LNA Design for UWBWLAN Transform-Domain Receiver Loss of Orthogonality It s important to note here the marginal dynamic feedback open loop contribution for the UWB WLAN LNA in terms of small signal gain Fig. 6 and NF Fig. 7 especially at the frequency band of interest. Thus the small signal gain improvement can be achieved without power noise amplification witch help improving the NF as needed. The frequency response simulation results suggest that for a specific inductive load range values L the closed loop feedback circuit contribution is effectively reduced to a simple zero at the origin Fig. 8 witch ensures a perfect stability for the LNA circuit over the entire UWB frequency band. However for other inductance L range values the UWB WLAN LNA could become deeply instable with four poles occupying a larger frequency range ex. L . The conversion gain can thus be maximized by introducing an optimum inductance L and capacitor C values L C until reaching 27dB at GHz Fig. 9 Fig. 10 . Fig. 6. The Dynamic Feedback Open Loop Gain Contribution. Fl eqilencf GHz Fig. 7. The Dynamic Feedback Open Loop Noise
