| With the continuous advancement of communication technology,communication systems are also developing in the direction of broadband and high frequency.Future ultra-wideband optical communication technology has high requirements for the bandwidth of optical driver amplifiers in the system,and wideband driver amplifiers need to be designed to meet the needs.Compared with other wideband amplifier structures,the distributed amplifier structure has the largest working bandwidth and better wideband performance,which is very suitable for application in ultra-wideband optical communication systems.This thesis first introduces the relevant performance indicators,classifications and common wideband amplifier structures of amplifiers,and provides a basis for selecting distributed amplifier structures by comparing the advantages and disadvantages of different wideband amplifier structures.Then,the design theory of distributed amplifier is studied,and the design method of distributed amplifier is studied,which provides a theoretical basis for the design of two subsequent distributed amplifiers based on 0.7 μm InP process.In the design,the first optical driver amplifier has high requirements for bandwidth and gain flatness,requiring its operating frequency coverage of 0.1-65 GHz and in-band gain flatness within±1d B.To this end,the amplifier adopts a four-stage distributed amplifier topology,in which in order to expand the bandwidth and reduce the parasitic capacitance of the transistor,the gain unit selects a smaller size transistor to form a Cascode structure,the transmission line selects a coplanar waveguide structure with small high-frequency loss,and the bias of the transistor is reasonably selected.In order to further expand the bandwidth to meet the needs of the index,a first-stage injection level follower is added before each stage of Cascode,so as to expand the bandwidth by reducing the parasitic capacitance of the gain unit input.The post-imitation results show that its operating frequency reaches 0.1-65 GHz,the in-band small signal gain S21 is 13.2d B,the gain flatness is within ±1d B,the input and output return loss is less than-10 d B,the in-band OP1 d B is between 7.3-10.5d Bm,and the stability coefficient is greater than 1 within 0-100 GHz,which meets the design index requirements.In addition to certain bandwidth requirements,the second optical driver amplifier also has high requirements for amplifier gain,requiring a gain of more than 17 d B in the operating frequency of0.1-45 GHz.To this end,increase the number of distributed amplifier stages to seven stages,the gain unit still adopts Cascode structure,in order to take into account the amplifier bandwidth and output capacity,the common injection tube uses a small size tube to ensure the bandwidth,the common base tube uses a large size tube to improve the output,the gain unit adds a peaked inductance to reduce the amplifier gain high-frequency roll-off,thereby improving the high-frequency gain flatness,the transmission line selects the microstrip line structure to complete,and the previous coplanar waveguide structure is compared for future improvements to the transmission line.The simulation results show that the amplifier has a small signal gain of 17.6d B and a gain flatness of±1.7d B within the operating frequency of 0.1-45 GHz,S11 and S22 are less than-10 d B,and the in-band OP1 d B is between 12.6-14.3d Bm. |
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