| Carbon nanotube transistor(Cnt)has been considered as an ideal semiconductor material for RF transistors because of its quantum capacitance,high electron mobility,potential cutoff frequency above THz and ballistic electron transport.So far,the high performance cnt FETs have been researched by the worldwide.However,besides the characteristics of cnt FET itself,for example,the DC characteristic,cutoff frequency and oscillation frequency,it is also important that the demonstration of cnt RF integrated circuit design,which means cnt can be substituted for the conventional semiconductor materials to design integrated circuits.The amplifiers are researched in this article,and the main research methods and achievements are as follows:1.As the efficiency of the conventional broadband power amplifiers is limited by the bandwidth itself,it is difficult for them to further improve the efficiency.The idea of bandwidth reconfiguration is proposed to further improve the efficiency through a narrower bandwidth.The bandwidth reconfiguration technology of distributed power amplifiers is researched.There are two types of the DPA,which are the nonuniform distributed power amplifier and the supply-scaling distributed power amplifier.And the topology of the supply-scaling distributed power amplifier is chosen to research the bandwidth reconfiguration technology,which produces lower efficiency and saturated output power,but is uniform structure and shows little different transmission lines when it shows 10GHz Ft and 18GHz Ft,after a comparison between the nonuniform distributed power amplifier and the supply-scaling distributed power amplifier.Furthermore,the supply-scaling distributed power amplifier is combined with rhe coupling capacitance technology and three technologies proposed by this article,which are the reconfigurable transmission line technology,the reconfigurable capacitance technology and the reconfigurable resistor technology.Then,a broadband high efficiency distributed power amplifier with reconfigurable bandwidth is designed.Among the three technologies,the reconfigurable transmission line technology is one of this paper's innovations.The reconfigurable transmission line is a transformer composed of a ring primary coil and a ring secondary coil with a switch.The equivalent inductance of the primary coil can be changed by adjusting the on-off of the secondary coil.And the ring primary coil is composed of two symmetrical gate lines.In this way,two reconfigurable transmission lines can be realized with one switch,which reduces the number of switches,thus reducing the loss introduced by the switch and meanwhile increasing the possibility that the chip can function successfully.Because the cnt process can't function successfully and it's lack of large-signal models needed for simulation,the broadband high efficiency distributed power amplifier with reconfigurable bandwidth is demonstrated with a 0.25 um Ga N process.However,as the chip will be fabricated in April this year,only layout simulation is used to demonstrate the design.The layout area is 3.85*1.7 mm2,and according to the results of the EM simulation,the design shows PAE>25%and output power>33 d Bm from2.5 to 17.8GHz,and PAE>30%from 3 to 14GHz and from 15.8 to 17.7GHz,and the peak output power is 36.2 d Bm,which demonstrate the correctness of the design method.2.In order to verify the performance of RF integrated circuits based on the cnt process,an X-band single frequency point amplifier based on 90nm cnt process is designed.From the perspective of RF performance,cnt FET has the characteristics of high-Q input impedance.Therefore,the L-type input matching network consumes a lot of energy,and then the input matching network of T-type matching network is designed to counteract the high Q value of the transistor by connecting a large inductor in front of the gate.Furthermore,a 2-stage common source cascaded amplifier and the corresponding layout are designed.Because the cnt process can't function successfully,the results of the EM simulation are used to demonstrate the design,which shows s11,s22<-10d B,and gain is 10.4d B-13.5d B from 8.6GHz to 8.9GHz with a bandwidth of0.3GHz.And The layout area is 1.1*2.3 mm~2.Although in the same frequency band,the gain of this design is about 10d B lower than that of the traditional process,this is related to the low transconductance of the cnt FET itself,which can be improved by the improvement of the cnt process.3.In order to verify the performance of broadband amplifier based on the cnt process,a distributed amplifier based on 90nm cnt process is designed.From the theory of distributed amplifiers,it is found that the high Q value input impedance of cnt FET is very suitable for the topology of distributed amplifier.At the same time,the topology of distributed amplifier can also solve the problem of narrow matching bandwidth caused by high Q value of the cnt FET.However,cnt has the problem of low transconductance.The technology of gate inductively peaking is proposed to improve the transconductance.Because the cnt process can't function successfully,the results of the EM simulation of a 5 stages distributed amplifier are used to demonstrate the design,which shows s11<-10d B,and s11 almost<-13d B,s22<-16d B,and gain is1.8d B-3.1d B from 6GHz to 18GHz with a bandwidth of 12GHz.cross the bandwidth.And The layout area is 3.2*3.5 mm2.Compared with the distributed amplifier designed by CMOS process,it can be seen that the gain bandwidth product of this amplifier is much lower than that of CMOS process,mainly because the transconductance,cutoff frequency and oscillation frequency of this process are inherently far lower than the CMOS processes,which can be eliminated by improving cnt process.In addition,the proposed amplifier operates up to frequencies as high as 0.96 f T of the transistors,which may be related to the cnt material itself.This inference needs to be verified by the subsequent work. |
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