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RFID cung cấp khả năng hiển thị 100% hàng tồn kho trong một chuỗi cung ứng, bất kể vị trí của nó. Hàng hóa có thể được di chuyển dễ dàng hơn và nhanh hơn trong chuỗi cung ứng như là một kết quả. Ngoài ra, năng suất trong vận chuyển và nhận có thể được cải thiện, | 104 STABILITY OF FEEDBACK AM FIERS and Equation 7.67 becomes f _ dc JV dc nux T cot pMựl COt2Ợ M. Jo 7.69 EXAMPLE 7.12. Feedback return FN of Example 7.11 is changed from a frequency-independent Fff_iQ to the F given by Equation 7.43a with fL 50 MHz and fv 250 MHz. Thus for pM 45 MdAX. 5MHz cot 45 Vl 707 707 707 FN d TOX - S 0.1414 5000 and MNdc mi ỡdxZ ÕJ4Ĩ4S 7 Note that this is a significant improvement over the MN dc mm 35 of Example 7.11. According to Equation 7.69 it is desirable to have fv as large as possible in order to be able to use a large value of AicFN dc. However the value of fv is constrained by Equations 7.43a-d. It will now be assumed and seen later that in practice the limitations on the choice of feedback capacitance CF do not limit the choice of other values in Equations 7.43a-d. Thus CF is eliminated by combining Equations 7.43b 7.43c and 7.43d resulting in -f Fn.0c 7 2kRfCj Ju Jl the required value of CF is given from Equation 7.43c as CF F 2nRFfL 7.70 7.71 To have fv large ỉ fv of Equation 7.70 has to be small. With corner frequency fL chosen to equal a corner frequency of the operational amplifier for a given FNic the only remaining avenue to reduce fv in Equation 7.70 is to reduce RfCị. It can be seen in Figure 7.4 that capacitance Cị is the sum of the operational amplifier input capacitance and of stray capacitances hence C cannot be reduced below a minimum value. This leaves feedback resistor Rf to be reduced. Resistance Rr can be expressed from Equation 7.70 as 7.6 PHASE MARGINS 105 where Rr 0 as a consequence of Equation 7.46. Note that the value of RF given by Equation 7.72 may be impractically low because the current required for a given output voltage swing may exceed the current capability of the output of the operational amplifier. Output current limitations of operational amplifiers will be discussed in Chapter 10. EXAMPLE 7.13. In the feedback amplifier of Example 7.12 fL 50 MHz fv 250 MHz and FNtic Ffl.dXa 0.1414. .
