Tham khảo tài liệu 'antennas with non-foster matching networks phần 4', kỹ thuật - công nghệ, kĩ thuật viễn thông phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 26 ANTENNAS WITH NON-FOSTER MATCHING NETWORKS Port P1 Num 1 P2 Num 2 -193 uV t-AMs nA Vr nA uA -456 uV -3I33 uA opa69 OP mA V_DC SRC4 Vdc 5 V R1 R 1 GOhm w mV 5 V 0 A----- ----- uAV-0 A mA mA A1 5 V V 5 V 0 A V 0 A C C8 C uF Port P3 Num 3 C C9 C uF -5 V 3 mA V- ỈV_DC SRC3 Vdc -5 V 0 A C C7 C uF FIGURE 26 Schematic ofOPA690 for simulation in Agilent ADS obtained by using the SPICE model and the data sheet for the device provided by TI performance of several of these NIC circuits. Unfortunately successful simulation of an NIC circuit has not always led us to a successful physical implementation. One reason for this is that all NIC circuits are only conditionally stable that is certain auxiliary conditions must be met for the circuit to be stable. In this section we will review our progress in physically realizing NIC circuits for use in active non-Foster matching networks. The reader should be aware that this topic is one for which a great deal of work remains to be done. It is this author s opinion that the major advances in this area will be made by analog circuit designers who have been convinced by antenna engineers of the rewards to be reaped in pursuing the development of high frequency NICs. Vg Rg Signal Generator V Rin in Iin neg NIC Zin -Zl FIGURE 27 Circuit for evaluating the performance of a grounded negative impedance ANTENNAS WITH NON-FOSTER MATCHING NETWORKS 27 The first NIC circuit that we consider is a grounded negative resistor GNR realized using the OPA690 op-amp from Texas Instruments TI . The OPA690 is a wideband voltagefeedback op-amp with a unity gain bandwidth of 500 MHz. Using the SPICE model for the device and the data sheet 11 provided by TI an Agilent ADS model of the OPA690 can be created as shown in Fig. 26. In this circuit port 1 is the noninverting input port 2 is the inverting input and port 3 is the single-ended output port. The uF capacitors are used to RF bypass
