tailieunhanh - Radio Frequency Identification Fundamentals and Applications, Design Methods and Solutions Part 6

Tham khảo tài liệu 'radio frequency identification fundamentals and applications, design methods and solutions part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Near Field On Chip RFID Antenna Design 117 Zrc Fig. 7. Z-Smith Chart and the location of the input impedance of the RFID Tag used ZRC. to get a good Q-factor of the OCA suitable values for equivalent impedance will be computed and analyzed. Besides capacitors influence only in imaginary part of the impedance within reactance part but not in resistance. According to all of these OCA resistance can be designed equally to the Tag resistance formula 14. Roca Rrc 80 a 14 On the other hand relationship between reactance and resistance given below 15 together with Q-factor around 3 provide a consistent and a reliable design of OCA s impedance. X Q - R . OCA 3R . -OCA OCA 15 As a result a consistent reactance for the tag antenna is XOCA 240a LOCA is concluded. The impedance of OCA could be ZOCA 80 j240 a and formula 16 shows the normalized value according to the characteristic impedance which is located at the up-hemisphere of the Smith Chart figure 8 ----- Z ZOCA -- 1 6 j4 6 OCA Z0 16 As it can be seen OCA impedance has an inductive feature which is coherent with the type of antenna a coil. It is actually an inductive set by both the reader and the Tag coils. In this case the matching area is the region inside of the Middle-Line and the frontier of the resistance and conductance in the down-hemisphere. An ideal case would be if OCA antenna Impedance is exactly as the Chip input one then no Matching network would be needed because both stages would be already matched figure 9. 118 Radio Frequency Identification Fundamentals and Applications Design Methods and Solutions Fig. 8. DP-Nr. 1 Q Q at GHz. Data Number Point Impedance Q Q-Factor 1 80-j240 2 80 j240 Table 1. Data Point Numbers with its corresponding impedance and Q-factor at 2 45 GHz. Fig. 9. Z-Smith Chart of the circuit impedance and its corresponding matching conjugated .