Công nghệ cơ khí thường tạo ra các giả lập mô phỏng hoạt động của các đối tượng, như quy trình chế tạo thực tế theo trình tự tối ưu hóa sự thực hiện, hiệu quả kinh tế và chi phí năng lượng trước khi quyết định lựa chọn một thiết kế cụ thể. | 84 Advanced Microwave Circuits and Systems required at . Also in this case the network exhibits the requested real part of the input impedance with a residual imaginary part of the input impedance. Fig. 8. S11 and S21 frequency behavior together with the real and imaginary parts of the input impedance when the switch is ON left and OFF right . 5. Dual-Band reconfigurable SiGe HBT amplifier design The above described matching network can been adopted to implement the two matching networks for a class-AB amplifier. In the following example of such design approach is presented. The design of the reconfigurable PA is based on a power device composed of 17x8 elementary SiGe HBT with and emitter area of pm2. The bias circuitry of the power section is designed to provide other than the required base bias current a circuit-level linearization. Let s start introducing this latter part referencing to the Fig. 9. The size of the devices used for the bias circuitry and the values of passive components scale accordingly so that accurate . matched current mirroring can take place. In addition resistor R4 introduces base ballasting and its value is selected to be 350 Q per emitter. It helps in reducing the risks due to thermal runaway. A larger value would have better effect however that could result in high DC voltage drop at high power drive and thus early gain compression of T4 the power transistor would take place. Fig. 9. PA core schematic including the power transistor and the bias network The power device which is shown in Fig. 9 within the dotted outline is biased through the current mirror. By inspection of this figure the current through the reference transistor T1 is Flexible Power Amplifier Architectures for Spectrum Efficient Wireless Applications 85 r VREF 2Vbe 9 REF R1 with Vbe V. If the ratio between the reference device and the RF device is M in this case M 17x8 then the current that will flow through the RF transistor is M Iref. in addition the
