Công nghệ cơ khí hay kỹ thuật cơ khí là ngành ứng dụng các nguyên lý vật lý để tạo ra các loại máy móc và thiết bị hoặc các vật dụng hữu ích. Cơ khí áp dụng các nguyên lý nhiệt động lực học, định luật bảo toàn khối lượng và năng lượng để phân tích các hệ vật lý tĩnh và động, phục vụ cho công tác thiết kế trong các lĩnh vực như ô tô, máy bay và các phương tiện giao thông khác, các hệ thống gia nhiệt và làm lạnh, đồ dùng gia đình, máy. | 144 Advanced Microwave Circuits and Systems 50 s 36 _ ĨỖPBỐ I 46 Ộ s 44 42 40 38 c g o 5 o Q 2 Time psec 1dB Comp Envelope output Pn avg pout ffz pin peak pout p peak -4 dBm p 45 dBm fif ideal 46 dBm out dBm p peak 47 dBm ideal 49 dBm Ppat 2 dBm P oU dBm pi -2 dBm p u 47 dBm UD 1UD 2 . -14 -12 -10 -8 -6 -4 -2 0 2 4 Instantenous input power dBm Fig. 6. Input output envelope variation of a two tone signal with respect to AM AM charac- teristic instantaneous power of the input output two-tone envelope signals are presented in comparison with the AM AM characteristic. All the parameters already defined are also shown on this figure Fig. 6 for this particular case. Therefore we conclude that the envelope variation of the two-tone signal makes it more vulnerable to nonlinearity. Besides it is important to note that for varying envelope signals it is very difficult to predict or to quantify the amount of gain compression at the output of the PA the OBO and OPBO values even in the case of deterministic signals like the two-tone signal. This is due to the fact that various parameters and nonlinear relations are involved. In general reducing the nonlinear distortion is at the expense of power efficiency. In fact the power efficiency of the PA is likely to increase when its operating point approaches the saturation. But for all the reasons already mentioned and in order to preserve the form of the envelope of the input signal large power backoffs are classically imposed. For an ideal amplification the IPBO must be sufficiently important to prevent the envelope from penetrating the compression region. Doing so the power efficiency of the PA decreases considerably especially if the input signal has a high PAPR value. In the second part of this chapter we will present an important technique used to resolve this problem. Distortion in RF Power Amplifiers and Adaptive Digital Base-Band Predistortion 145 Interception Points In the one-tone test the nth .
