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华中科技大学题目：比例放大器设计院 系：专业班：姓 名：学 号：指导教师：20XX年XX 月摘要在模拟电路中对放大器进行设计时，差分放大器由于能够实现两倍放大和能够很好的抑制共模噪声的优良性能而被广为应用。本文利用放大器的“虚短”“虚断”的特性对比例放大器的结构及放大器的构成和基本参数进行了设计，其中放大器采用差分放大结构。关键词：比例放大器 差分放大器 一级结构 二级结构AbstractWhen designing an amplifier, differential amplifiers,with its twice higher gain and its restrain to Common-mode disturbance,is more widely used than other kinds of amplifiers.In this report,we make use of the properties of “virtual short cicuit” and “virtual disconnection” and design the structure and parameters of the whole circuit as well as the structure of the amplifier.Key Words：Proportion amplifier Differential amplifiers Level 1 Level 2目录摘要IABSTRACTI1 题目要求12 设计过程22.1 基本结构及分析.22.1.1 外围电路分析22.1.2 运算放大器选择32.2 工艺参数提取.32.3 理论推导与计算.52.4 仿真.62.5 二级密勒补偿运算放大器.102.6 仿真结果.132.7 综合仿真.173 结果分析与结论224 心得体会23致 谢.25参考文献26附录271 题目要求设计一个比例放大器，参考电路如下：要求：（1） 自行设计放大器的结构与MOS尺寸参数、电阻R1、R2的阻值，以达到相关性能指标；（基于0.35um COMS工艺，MOS管长度均设定为Lmin=1um）（2） 用HSPICE软件仿真电路。（3）电路性能指标满足如下要求： ；相位裕度 45度65度；输入信号频率；输出电流2 设计过程2.1 基本结构及分析2.1.1.外围电路分析指标要求中隐含了增益要大于10倍，带宽大于100MHZ，暂时不考虑相位裕度。如图结构来说，根据放大器的“虚短”、“虚断”特性，可以列出如下等式：根据题目要求： Vin:Vout=1:10因此，有： R1=9R2又： Iout=Vin/R2=10mA,Vin=1+0.1cos(wt)得：另外，信号中包含1V直流电压，相当于为放大器提供了直流偏置且Vo=10Vin=1v，取工作电压为单电源3v外围电路设计至此结束，现在进行放大器内部设计。2.1.2运算放大器选型 由于输入信号的特点，其中同时包含了直流与交流电压，考虑到信号噪声以及直流电压波动，使用差分放大电路能对共模输入起到很好的抑制作用，因此本设计选用差分放大电路。由于差分放大电路增益并不算高，实际中多采用Pmos有源负载以提高增益。在这里，我们选用以电流镜为负载的差分放大器实现所要求的运算放大器。电路如图所示：图1NMOS器件M1 和M2 作为差分对管，PMOS器件M4，M5 组成电流源负载。电流Io提供差分放大器的偏置电流。其中M1、M2参数全同，M3、M4参数全同。，设所有管子都工作在饱和区，如果Vgs1=Vgs2，由对称性，Id1=Id2=Id3=Id4。差分放大电路的输入输出有许多组合，本设计仅采用双端输入单端输出，因而本文仅对这种情况简要介绍。当从Vi1输入差模信号，Vi2=0（交流小信号），设Vgs1增大，则相应Id1变大，Id2变小，输出电压Vo=Id2*Ro；当输入共模信号，Vgs1恒等于Vgs2，则Id2不变，输出电压也不变。这样就相当于差模输入放大，而共模输入抑制。下面对具体参数进行设计。2.2 工艺参数提取 重要工艺参数并没有在本设计使用的0.35um工艺库中直接提供，需要提取。工艺库提供的参数为：Tox= 7.00000E-09 mUn= 4.0045690E+02 cm2/(VS)Up= 1.7853294E+02 cm2/(VS)由 K=0.5Cox 得为求值，需要对单个MOS管进行输出特性仿真。仿真电路如下： 得到如下曲线由 K已知 取WL=1，固定Vgs，则在饱和区取两数据点可得仿真单个nmos管特性vgs = 3.0000 vth=604.6282mvdsid4.2 222.9325u 4.3 223.1347u Kn=200 lambdan=0.01仿真单个pmosvgs = -3.5000vth=883.4507mvdsid-3.6-108.9378u-3.5-108.5570uKp=44lambdap=0.042.3 理论推导与计算对于上图所示差分放大器，电压增益为其小信号等效电路如下：列出电路的传递方程：第一极点可近似为,因为.在达到第一极点之前，从传递函数知增益恒定，当接近第一极点时，电路的增益开始下降，在=时，增益下降3db，之后增益以-20db/dec的速度开始下降，直到接近第二个极点。对于一级放大而言第二极点的影响可以暂时不考虑。由 又 则f1由、负载电容、电流共同决定，其中Cl不变，为工艺限制参数，则f1只能由Id决定。取（参考文献【1】） =200该设计最小增益应该为10倍，带宽100MHZ，GBW=109则f1=GBW/A0=5MHZ本设计取取f1为10MHz，=5pf，则=6.25mA，则根据上式计算可得=320。最后，由于和都已确定。可根据MOS管在饱和区的电流特性分别得出M1，M2的宽长比为,M3，M4的宽长比为。（注：本文未作特殊说明处均取L=1um）此电路中用作恒流源电流等于两支路电流之和，.2.4 仿真网表见附录。电路如图：结果如下：静态工作点(略去不关心的参数)* mosfets subckt element 0:m1 0:m2 0:m3 0:m4 model 0:n_33 0:n_33 0:p_33 0:p_33 region Saturation Saturation Saturation Saturation id 6.2500000m 6.2500000m -6.2500000m -6.2500000m vgs 959.7753743m 959.7753743m -1.0482749 -1.0482749 vds 1.9115004 1.9115004 -1.0482749 -1.0482749 * ac analysis * freq volt db volt phase vo vo 1.00000000 15.0444475 -6.8749998u 1.25892541 15.0444475 -8.6551116u 1.58489319 15.0444475 -10.8961398u 1.99526231 15.0444475 -13.7174277u 2.51188643 15.0444475 -17.2692179u 3.16227766 15.0444475 -21.7406582u 3.98107171 15.0444475 -27.3698659u 5.01187234 15.0444475 -34.4566210u 6.30957344 15.0444475 -43.3783131u 7.94328235 15.0444475 -54.6100615u 10.00000000 15.0444475 -68.7499949u 12.58925412 15.0444475 -86.5511176u 15.84893192 15.0444475 -108.9614004u 19.95262315 15.0444475 -137.1742793u 25.11886432 15.0444475 -172.6921768u 31.62277660 15.0444475 -217.4065723u 39.81071706 15.0444475 -273.6986679u 50.11872336 15.0444475 -344.5661914u 63.09573445 15.0444475 -433.7831586u 79.43282347 15.0444475 -546.1006154u 100.00000000 15.0444475 -687.4999672u 125.89254118 15.0444475 -865.5111389u 158.48931925 15.0444475 -1.0896140m 199.52623150 15.0444475 -1.3717428m 251.18864315 15.0444475 -1.7269218m 316.22776602 15.0444475 -2.1740657m 398.10717055 15.0444475 -2.7369866m 501.18723363 15.0444475 -3.4456621m 630.95734448 15.0444475 -4.3378314m 794.32823472 15.0444468 -5.4610069m 1.00000000k 15.0444468 -6.8750002m 1.25892541k 15.0444468 -8.6551119m 1.58489319k 15.0444469 -10.8961405m 1.99526231k 15.0444470 -13.7174278m 2.51188643k 15.0444471 -17.2692181m 3.16227766k 15.0444466 -21.7406584m 3.98107171k 15.0444463 -27.3698646m 5.01187234k 15.0444454 -34.4566182m 6.30957344k 15.0444448 -43.3783081m 7.94328235k 15.0444434 -54.6100491m 10.00000000k 15.0444413 -68.7499679m 12.58925412k 15.0444376 -86.5510585m 15.84893192k 15.0444317 -108.9612810m 19.95262315k 15.0444233 -137.1740313m 25.11886432k 15.0444093 -172.6916801m 31.62277660k 15.0443869 -217.4055933m 39.81071706k 15.0443509 -273.6966956m 50.11872336k 15.0442953 -344.5622438m 63.09573445k 15.0442062 -433.7752833m 79.43282347k 15.0440652 -546.0849237m 100.00000000k 15.0438423 -687.4685801m 125.89254118k 15.0434883 -865.4485719m 158.48931925k 15.0429273 -1.0894891 199.52623150k 15.0420385 -1.3714937 251.18864315k 15.0406299 -1.7264248 316.22776602k 15.0383991 -2.1730745 398.10717055k 15.0348654 -2.7350096 501.18723363k 15.0292713 -3.4417201 630.95734448k 15.0204197 -4.3299757 794.32823472k 15.0064266 -5.4453629 1.00000000x 14.9843422 -6.8438814 1.25892541x 14.9495683 -8.5933212 1.58489319x 14.8950183 -10.7737801 1.99526231x 14.8099391 -13.4761601 2.51188643x 14.6784156 -16.7965871 3.16227766x 14.4777810 -20.8238533 3.98107171x 14.1776087 -25.6168764 5.01187234x 13.7405937 -31.1720847 6.30957344x 13.1269495 -37.3888761 7.94328235x 12.3029068 -44.0530381 10.00000000x 11.2507989 -50.8611976 12.58925412x 9.9752452 -57.4890925 15.84893192x 8.5011802 -63.6724830 19.95262315x 6.8650378 -69.2582902 25.11886432x 5.1045630 -74.2090982 31.62277660x 3.2516690 -78.5756153 39.81071706x 1.3292659 -82.4605664 50.11872336x -649.2715511m -85.9880767 63.09573445x -2.6795662 -89.2810159 79.43282347x -4.7654994 -92.4424422 100.00000000x -6.9182417 -95.5357831 125.89254118x -9.1542038 -98.5607973 158.48931925x -11.4904723 -101.4294048 199.52623150x -13.9368596 -103.9572096 251.18864315x -16.4863334 -105.8946513 316.22776602x -19.1096238 -107.0079185 398.10717055x -21.7605042 -107.1775145 501.18723363x -24.3917334 -106.4476598 630.95734448x -26.9722354 -104.9820629 794.32823472x -29.4939701 -102.9514691 1.00000000g -31.9646259 -100.4269566电压增益只有15DB，带宽为8M，GBW=4.5107109 无法达到指标。从推导中可以看到，无论增益还是带宽，都相对固定，改动的余地不大，再加上器件的宽长比有限制，所以在这种情况下要增加增益而不太多的牺牲带宽是不太可能的。事实也证明用这样一级差分放大要达到指标还是相当困难的，多次修改参数后，任然没有达到理想的效果。参考文献【2】中对这种情况进行了介绍。2.5 二级密勒补偿运算放大器 二级密勒补偿运放是一种性能相对优越的结构，由于采用两级放大，能够提供相当大的增益，而带宽可以通过RC反馈网络进行一定的调节，这样一来可以达到最大GBW。于是采用如下电路对放大器进行设计。 如图所示，PMOS M1、M2为一级差分放大，NMOS M3、M4做镜像电流源负载，PMOS M6为第二级放大。电容和电阻Rz构成密勒补偿。二级密勒补偿运放的增益一般可以达到60db以上，本设计取增益为60db，带宽100M最简小信号等效电路如下：得到又，取则在过驱动电压等于0.2V时，增益远满足设计要求。设、分别为第一、二节点的对地电容，则电路的传输函数为（注意：没有算上Rz）其中则第一转折频率为那么第二转折频率为RC电路其实为超前补偿装置，使电路的相角超前，电路零点为将零点移至转折频率附近则能减缓增益下降的速率，这就相当于再增加了带宽。由于相位有45以上的要求，应使零点z位于1.2GBW处，并且让极点p2位于1.5GB处。（参考文献【1】）取根据设计要求，将所有的驱动电压都固定在0.2v，补偿电容已定则取 又因为且 取0.2V计算得出为200，用同样的方法计算得出为了实现相位补偿，让零点z位于1.2GB处。因此，即 由于 取 让极点p2位于1.5GB处，有 其中Cn3为3点对地电容，包括，其中 Cgs6占大部分。取，由前面的计算可知，= 0.003 计算得 2.6仿真结果仿真网表见附录电路如图：对以上计算参数仿真后发现GBW仅停留在8107比单级没有多少改善，但是根据GBW与gm1成正比的关系，以及Cc与带宽成反比的关系，多次调整参数使得单位增益带宽增大到了108。结果如下：* mosfets subckt x1 x1 x1 x1 element 1:m1 1:m2 1:m3 1:m4 model 0:p_33 0:p_33 0:n_33 0:n_33 region Saturation Saturation Saturation Saturation id -99.9999977u -99.9999977u 99.9999981u 99.9999981uvgs -1.0473706 -1.0473706 954.6972789m 954.6972789m vds -1.0926733 -1.0926733 954.6972789m 954.6972789m vth -829.4162414m -829.4162414m 655.5068344m 655.5068344m subckt x1 element 1:m6 model 0:n_33 region Saturation id 599.9999862u vgs 954.6972789m vds 6.8990087 vth 657.0844360m* *two-stage op amp * ac analysis tnom= 27.000 temp= 27.000 * x freq volt db volt phase vo vo 1.00000000 59.2376212 179.9995354 1.25892541 59.2376212 179.9994151 1.58489319 59.2376212 179.9992637 1.99526231 59.2376212 179.9990731 2.51188643 59.2376212 179.9988331 3.16227766 59.2376212 179.9985309 3.98107171 59.2376213 179.9981505 5.01187234 59.2376213 179.9976717 6.30957344 59.2376213 179.9970688 7.94328235 59.2376213 179.9963098 10.00000000 59.2376213 179.9953543 12.58925412 59.2376213 179.9941515 15.84893192 59.2376213 179.9926371 19.95262315 59.2376214 179.9907307 25.11886432 59.2376214 179.9883306 31.62277660 59.2376210 179.9853091 39.81071706 59.2376211 179.9815053 50.11872336 59.2376208 179.9767165 63.09573445 59.2376201 179.9706879 79.43282347 59.2376196 179.9630982 100.00000000 59.2376189 179.9535434 125.89254118 59.2376171 179.9415146 158.48931925 59.2376145 179.9263713 199.52623150 59.2376100 179.9073069 251.18864315 59.2376034 179.8833064 316.22776602 59.2375931 179.8530916 398.10717055 59.2375762 179.8150535 501.18723363 59.2375500 179.7671666 630.95734448 59.2375080 179.7068811 794.32823472 59.2374420 179.6309870 1.00000000k 59.2373366 179.5354439 1.25892541k 59.2371696 179.4151660 1.58489319k 59.2369058 179.2637526 1.99526231k 59.2364869 179.0731491 2.51188643k 59.2358239 178.8332232 3.16227766k 59.2347726 178.5312334 3.98107171k 59.2331075 178.1511686 5.01187234k 59.2304692 177.6729300 6.30957344k 59.2262913 177.0713310 7.94328235k 59.2196782 176.3148943 10.00000000k 59.2092179 175.3644490 12.58925412k 59.1926904 174.1715867 15.84893192k 59.1666239 172.6771392 19.95262315k 59.1256300 170.8100789 25.11886432k 59.0614410 168.4876286 31.62277660k 58.9616124 165.6180622 39.81071706k 58.8079502 162.1085678 50.11872336k 58.5750291 157.8813168 63.09573445k 58.2296995 152.9001536 79.43282347k 57.7330906 147.2056929 100.00000000k 57.0465858 140.9463836 125.89254118k 56.1414231 134.3825597 158.48931925k 55.0080926 127.8448309 199.52623150k 53.6598515 121.6565463 251.18864315k 52.1278794 116.0600933 316.22776602k 50.4514403 111.1833638 398.10717055k 48.6687302 107.0501110 501.18723363k 46.8116340 103.6130369 630.95734448k 44.9042636 100.7879153 794.32823472k 42.9637133 98.4783063 1.00000000x 41.0016016 96.5898510 1.25892541x 39.0256063 95.0368641 1.58489319x 37.0407064 93.7442778 1.99526231x 35.0500778 92.6471446 2.51188643x 33.0557109 91.6890118 3.16227766x 31.0588097 90.8198653 3.98107171x 29.0600369 89.9939583 5.01187234x 27.0596556 89.1676389 6.30957344x 25.0575848 88.2971884 7.94328235x 23.0533797 87.3366341 10.00000000x 21.0461390 86.2354892 12.58925412x 19.0343182 84.9363907 15.84893192x 17.0154123 83.3726641 19.95262315x 14.9854519 81.4659702 25.11886432x 12.9382482 79.1244411 31.62277660x 10.8642961 76.2421629 39.81071706x 8.7492795 72.7015437 50.11872336x 6.5722699 68.3811035 63.09573445x 4.3039825 63.1717286 79.43282347x 1.9060111 57.0033388 100.00000000x -667.5973074m 49.8784239 125.89254118x -3.4655061 41.8989529 158.48931925x -6.5324984 33.2669243 199.52623150x -9.9060166 24.2540763 251.18864315x -13.6203910 15.1773493 316.22776602x -17.7153072 6.4441015 398.10717055x -22.2346991 -1.3143724 501.18723363x -27.2047219 -7.1053656 630.95734448x -32.5972523 -9.5210330 794.32823472x -38.2763230 -6.6980266 1.00000000g -43.8558399 3.4982024 Y增益59.2376212db带宽125KHZ GBW=1.14108Bode图如下： 相位裕度大约50其实结果有可能更好，因为GBW和Cc、gm1的关系相对独立，修改这两个参数并不大规模影响电路的特性，由它们变化而产生的相位裕度的降低可以由Rz进行补偿。如果耐心调试可以将GBW调整至1092.7 综合仿真电路如下：仿真网表如下：*Two-Stage Op Amp.option post=2 numdgt=7 tnom=27.LIB C:synopsysHspice2005.03BINCMOS_035_Spice_Model.lib ttvdd VDD 0 3电源电压3vvi1 Vi1 0 dc=1 ac=0.1 共模电压1v 交流电压0.1vvi2 Vi2 0 dc=1 ac=0 r1 Vo R2 900900欧r2 R2 0 100100欧*cl Vo 0 3pf负载开路x1 VDD 0 Vi1 Vi2 Vo opamp二级运放子电路接口：VDD VSS 输入1 输入2 输出.subckt opamp VDD 0 Vi1 Vi2 VoM1 1 Vi1 3 3 p_33 W=57U L=1U M2 2 Vi2 3 3 p_33 W=57U L=1U M3 1 1 0 0 n_33 W=13U L=1U M4 2 1 0 0 n_33 W=13U L=1U M6 Vo 2 0 0 n_33 W=38U L=1Urz 2 4 380补偿电阻 380欧cc 4 Vo 1pf补偿电容 1pfIref1 VDD 3 dc 200U静态偏置200UIref2 VDD Vo dc 600UM6偏置600 U （3gm1=gm6）.ends.op.ac dec 10 1 1G.print ac vdb(Vo) vp(Vo).end结果如下： freq volt db volt phase vo vo 1.00000000 19.2671363 179.9999204 1.25892541 19.2671363 179.9998998 1.58489319 19.2671363 179.9998738 1.99526231 19.2671363 179.9998411 2.51188643 19.2671363 179.9998000 3.16227766 19.2671363 179.9997482 3.98107171 19.2671363 179.9996830 5.01187234 19.2671363 179.9996009 6.30957344 19.2671363 179.9994976 7.94328235 19.2671363 179.9993675 10.00000000 19.2671363 179.9992037 12.58925412 19.2671363 179.9989976 15.84893192 19.2671363 179.9987380 19.95262315 19.2671363 179.9984112 25.11886432 19.2671363 179.9979999 31.62277660 19.2671363 179.9974820 39.81071706 19.2671364 179.9968300 50.11872336 19.2671364 179.9960092 63.09573445 19.2671364 179.9949759 79.43282347 19.2671364 179.9936750 100.00000000 19.2671364 179.9920373 125.89254118 19.2671365 179.9899756 158.48931925 19.2671366 179.9873800 199.52623150 19.2671367 179.9841123 251.18864315 19.2671360 179.9799986 316.22776602 19.2671363 179.9748197 398.10717055 19.2671359 179.9682999 501.18723363 19.2671348 179.9600920 630.95734448 19.2671334 179.9497588 794.32823472 19.2671317 179.9367501 1.00000000k 19.2671285 179.9203730 1.25892541k 19.2671235 179.8997556 1.58489319k 19.2671160 179.8737999 1.99526231k 19.2671039 179.8411236 2.51188643k 19.2670838 179.7999868 3.16227766k 19.2670535 179.7481989 3.98107171k 19.2670043 179.6830024 5.01187234k 19.2669270 179.6009260 6.30957344k 19.2668051 179.4976004 7.94328235k 19.2666101 179.3675257 10.00000000k 19.2663030 179.2037808 12.58925412k 19.2658145 178.9976568 15.84893192k 19.2650419 178.7381994 19.95262315k 19.2638168 178.4116361 25.11886432k 19.2618761 178.0006653 31.62277660k 19.2588024 177.4835791 39.81071706k 19.2539348 176.8331942 50.11872336k 19.2462319 176.0155789 63.09573445k 19.2340519 174.9885896 79.43282347k 19.2148161 173.7003021 100.00000000k 19.1845044 172.0875676 125.89254118k 19.1368922 170.0751921 158.48931925k 19.0624851 167.5767276 199.52623150k 18.9471082 164.4986338 251.18864315k 18.7703037 160.7504923 316.22776602k 18.5040467 156.2644521 398.10717055k 18.1128890 151.0253133 501.18723363k 17.5571661 145.1062858 630.95734448k 16.8003691 138.6938350 794.32823472k 15.8192737 132.0776489 1.00000000x 14.6119687 125.5940849 1.25892541x 13.1985695 119.5447228 1.58489319x 11.6141082 114.1332424 1.99526231x 9.8983473 109.4476717 2.51188643x 8.0877540 105.4809973 3.16227766x 6.2116468 102.1663588 3.98107171x 4.2916602 99.4084133 5.01187234x 2.3428893 97.1041483 6.30957344x 375.4848459m 95.1539375 7.94328235x -1.6038865 93.4658637 10.00000000x -3.5909239 91.9561480 12.58925412x -5.5828897 90.5475211 15.84893192x -7.5780742 89.1665965 19.95262315x -9.5754493 87.7407511 25.11886432x -11.5744553 86.1947059 31.62277660x -13.5748866 84.4468406 39.81071706x -15.5768573 82.4052058 50.11872336x -17.5808403 79.9632056 63.09573445x -19.5878130 76.9950329 79.43282347x -21.5995619 73.3512290 100.00000000x -23.6192799 68.8554600 125.89254118x -25.6526966 63.3051139 158.48931925x -27.7100940 56.4816143 199.52623150x -29.8095351 48.1819942 251.18864315x -31.9808622 38.2900005 316.22776602x -34.2679084 26.9032989 398.10717055x -36.7239649 14.5039587 501.18723363x -39.3973062 2.1100581 630.95734448x -42.3076122 -8.6418797 794.32823472x -45.3946146 -15.4405585 1.00000000g -48.3613982 -15.53892233结果分析与结论通过对整个电路的分析、设计与仿真可以看出，当增益较大时，仅用一级差分放大器很难达到设计的要求。这时可以考虑采用二级放大器。在对二级差分放大器进行设计时，要对增益、单位增益带宽。相位裕度、幅频特性等多方面进行综合考虑。采用二级差分放大器时，电路的主要参数为对M1、M2 对M3、M4对M6 仿真得到的结果增益59.2376212db带宽125KHZ GBW=1.14108相角裕度约为50与一级放大器相比较性能得到明显提高。当对整个负反馈电路进行综合仿真时，将Cl断开，取补偿电阻380欧，补偿电容1pf静态偏置200U，M6偏置600 U。则电压增益约为9.38，输入频率范围为1Mhz4心得体会略致谢略参考文献略附录仿真网表如下：*Two-Stage Op Amp.option post=2 numdgt=7 tnom=27.LIB C:synopsysHspice2005.03BINCMOS_035_Spice_Model.lib ttvdd
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