ADS設(shè)計VCO范例(不錯)

1、應(yīng)用ADS設(shè)計VCO1.VCO振蕩器的基本知識和相關(guān)指標(biāo)1.1振蕩器的分類：微波振蕩器按器件來分可以分為：雙極晶體管振蕩器；場效應(yīng)管振蕩器；微波二極管(踢效應(yīng)管、雪崩管等)振蕩器。按照調(diào)諧方式分可以分為：機械調(diào)諧振蕩器；偏置調(diào)諧振蕩器；變?nèi)莨苷{(diào)諧振蕩器；YIG調(diào)諧振蕩器；數(shù)字調(diào)諧振蕩器；光調(diào)諧振蕩器。1.2 振蕩器的主要指標(biāo)： 振蕩器的穩(wěn)定度：這里面包括：頻率準(zhǔn)確度、頻率穩(wěn)定度、長期穩(wěn)定度、短期穩(wěn)定度和初始漂移。頻率準(zhǔn)確度是指振蕩器實際工作頻率與標(biāo)稱頻率之間的偏差。有絕對頻率準(zhǔn)確度和相對頻率準(zhǔn)確度兩種方法表示。絕對頻率準(zhǔn)確度：其中實際工作頻率；標(biāo)稱頻率。相對頻率準(zhǔn)確度式絕對頻率準(zhǔn)確度與標(biāo)稱頻率

2、準(zhǔn)確度的比值，計算公式為： 頻率穩(wěn)定度：頻率穩(wěn)定度是指在規(guī)定的時間間隔內(nèi)，頻率準(zhǔn)確度變化的最大值，也有兩種表示方法：絕對頻率穩(wěn)定度和相對頻率穩(wěn)定度。頻率穩(wěn)定度還可以分為長期頻率穩(wěn)定度、短期頻率穩(wěn)定度和瞬間頻率穩(wěn)定度。 調(diào)頻噪音和相位噪音：在振蕩器電路中，由于存在各種不確定因素的影響，使振蕩頻率和振蕩幅度隨機起伏。振蕩頻率的隨機起伏稱為瞬間頻率穩(wěn)定度，頻率的瞬間變化將產(chǎn)生調(diào)頻噪音、相位噪音和相位抖動。振蕩幅度的隨機欺負(fù)將引起調(diào)幅噪音。一次，振蕩器在沒有外加調(diào)制時，輸出的頻率不僅含振蕩頻率f0，在f0附近還包含有許多旁頻，連續(xù)分布在f0兩邊。如下圖所示，縱坐標(biāo)是功率，f0處是載波，兩邊是噪音功率，

3、包括調(diào)頻噪音功率和調(diào)幅噪音功率。圖1正弦信號的噪聲邊帶頻譜圖2 相位噪聲的定義如圖2所示，（單邊帶）相位噪聲通常用在相對于載波某一頻偏處，相對于載波電平的歸一化1Hz帶寬的功率譜密度表示（dBc/Hz）。1. 3振蕩器的物理模型下圖所示的是振蕩器的物理模型，主要由諧振網(wǎng)絡(luò)、晶體管和輸入網(wǎng)絡(luò)這三部分組成。圖3本節(jié)論述的振蕩器采用共基極反饋振蕩器，這種類型的振蕩器的物理模型如下圖所示。圖4圖5電路組態(tài)在微波頻率范圍內(nèi)的低頻端，常應(yīng)用集中元件構(gòu)成振蕩器，基本的振蕩器電路組態(tài)有三種：考畢茲型、哈特萊型及克拉潑型振蕩器。如圖5所示?？籍吰澬?a)應(yīng)用一電容器作為調(diào)諧電路中的分壓器，以提供適當(dāng)?shù)幕厥谀芰俊?/p>

4、哈特萊型(b)應(yīng)用一抽頭式電感調(diào)諧電路，而克拉潑型振蕩器(c)則相似于考畢茲型，不同的式另外用了一只電容與電感相串連，以改善頻率穩(wěn)定性。在較高的微波頻段內(nèi)，晶體管的極間電容、包括封裝寄生電容可提供部分或者全部的回授作用。另外加入反饋網(wǎng)絡(luò)的目的，則在于增加負(fù)阻電阻值，以獲得最佳功率輸出。 振蕩器的直流偏置：微波雙極晶體管、場效應(yīng)晶體管偏置電路的設(shè)計如同振蕩器的射頻電路設(shè)計一樣重要。因為它關(guān)系到微波振蕩的穩(wěn)定性、相位噪音、功率、效率的高低，故應(yīng)當(dāng)正確設(shè)計偏置電路，并選擇最佳直流工作點，以達(dá)到最高的射頻性能。設(shè)計的原則取決于應(yīng)用。例如用作低噪聲振蕩器：采用硅雙極晶體管時Vce可以在510V、Ice可

5、在38mA內(nèi)選擇；采用砷化鎵場效應(yīng)管時VDS大概為3.5V，IDS大概為810mA，一般選擇相當(dāng)?shù)偷穆┰措妷篤DS和電源IDS。1. 4微固態(tài)振蕩源的設(shè)計方法微固態(tài)振蕩源的傳統(tǒng)設(shè)計方法，是設(shè)計者從給定的技術(shù)指標(biāo)出發(fā)，選擇振蕩器件及電路形式，按簡化的等效電路或圖解方法，按照現(xiàn)有的設(shè)計資料或者以往的經(jīng)驗，初步設(shè)計制成電路，調(diào)測其特性，然后根據(jù)所測性能與技術(shù)要求進(jìn)行比較。如果不滿足給定指標(biāo)，再修改電路直到滿足要求為止。而引入了微波電路設(shè)計CAD后，這個過程可以作出適當(dāng)?shù)恼{(diào)整，調(diào)整為：定模、分析、最優(yōu)化。2 設(shè)計目標(biāo)設(shè)計一個VCO，要求工作在2.3GHz左右，帶寬為400MHz左右。3硅雙極性管等效模

6、型分析模型本節(jié)的振蕩器采用HP公司生產(chǎn)的AT41411硅雙極管。主要的指標(biāo)有：低噪音特性：1GHz時噪音系數(shù)是1.4dB；2GHz時噪音系數(shù)是1.8dB；高增益：1GHz是增益為18dB；2GHz時增益為13dB；截至頻率是：7GHz，有足夠?qū)挼念l帶；直流偏置：Vce8V；Ic10 mA封裝形式：STO143 因為該振蕩器工作的頻率有2GHz這么高，這個時候晶體管之間的結(jié)電容和封裝管子引入的引線電感和分布電容就必須要考慮了。圖6是雙極性硅管的高頻信號模型，具體的典型參數(shù)值在后表。圖7是考慮了封裝后的雙極性硅管的高頻信號模型，具體的典型參數(shù)值也見后表。由于這些參數(shù)HP公司是沒有提供的，只提供了S

7、參數(shù)，所以我們不能用這種小信號模型來做仿真，只能利用這些小信號模型來估算振蕩器其他部件的參數(shù)值。HP_AT41411在ADS的器件庫里面帶有，可以直接使用。圖6圖7符號元件名典型值Re2發(fā)射極擴展電阻8.6 ohmRe1發(fā)射極空間電荷電阻0.7 ohmRs集電極擴展電阻7.0 ohmCe發(fā)射極基極結(jié)電容1.0 pFCc集電極發(fā)射極電容0.005 pFCce集電極發(fā)射極電容0.05 pFRb基極擴展電阻14.7 ohmo零頻率是共基極電流放大倍數(shù)0.99表1 硅雙極管管芯等效電路元件典型值符號元件名典型值C1、C2各封裝點之間的電容C1:0.06-0.1 pFC2:0.01-0.012 pFC3

8、:0.001-0.003 pFC4:0.01-0.013 pFC3、C4C5輸出、輸入端之間的電容0.005 pFL1、L4參考面與封裝邊緣之間的引線電感L1:0.2-0.3nH；L4:0.4-0.6nHL2、L3封裝邊緣與金屬絲接點之間的引線電感0.2-0.5nHL5芯片至發(fā)射極端子的金絲電感0.3-0.6nH表2 封裝參數(shù)典型值4 確定實際電路圖8是本節(jié)振蕩器采用的具體電路，其電路結(jié)構(gòu)如圖9所示圖8圖9把結(jié)電容和封裝電感、電容考慮進(jìn)去后，振蕩器的諧振回路等效為圖10所示，這樣需要設(shè)計的只有：偏置電路、變?nèi)莨艿腣C特性和振蕩器的調(diào)試以及相位噪音分析。圖10 諧振回路等效電路5 具體設(shè)計過程5

9、.1創(chuàng)建一個新項目 啟動ADS 選擇Main windows 菜單FileNew Project，然后按照提示選擇項目保存的路徑和輸入文件名 點擊“ok”這樣就創(chuàng)建了一個新項目。 點擊，新建一個電路原理圖窗口，開始設(shè)計振蕩器。5.2偏置電路設(shè)計 在電路原理圖窗口中點擊，打開Component library 按“ctrl+F1”打開搜索對話窗口 搜索器件“ph_hp_AT41411”這就是我們在該項目中用到的Agilent公司的晶體管 把搜索出來的器件拉到電路原理圖中，按“Esc”鍵可以取消當(dāng)前的動作。 選中晶體管，按可以旋轉(zhuǎn)晶體管，把晶體管安放到一個合適的位置。 在中選擇probe comp

10、onents 類，然后在這個類里面選擇并安放在適當(dāng)?shù)奈恢?，同理可以在“SourcesTime Domain”里面選擇，在lumped components里面選擇，并按照圖11放好。 在optim/stat/Yield/DOE類里面選擇，這里需要兩個，還有一個 在SimulationDC里面選擇一個 上面的器件和仿真器都按照下圖11放好，并單擊連好線 按這時會出現(xiàn)一個這樣的對話框，輸入你需要的名字并在你需要的電路圖上面點一下，就會自動給電路接點定義名字，如圖11所示定義“Vcb”，“Veb”節(jié)點名稱圖11直流偏置計算 雙極，把該I_Probe的名稱改為ICC 同樣，另外一個接晶體管S極的I_P

11、robe改為“IEE” 雙擊其中一個并修改里面的內(nèi)容，如圖12所示圖12 雙擊另外一個，并修改里面的內(nèi)容如圖13所示圖13 雙擊并把里面的Optimization Type修改為“Gradient”類型 把接在“C極”上的電阻改為，把電源改為“12V” 把接在“S極”上的電阻改為，把電源改為“5V” 按“F7”快捷鍵進(jìn)行仿真 在Data Display窗口，就是新出來的窗口中，按鍵，會選擇“R.R1；R.R2”這樣就會顯示出優(yōu)化的直流電阻的數(shù)值，如圖14所示。圖145.3變?nèi)莨軠y量 新建一個電路原理圖窗口 如上面的做法一個，建立如圖15所示的電路圖，其中“Term”、“S-PARAMETE”、

12、“PARAMETER SWEEP”都可以在“SimulationS_Param”里面找到。變?nèi)莨艿男吞柺恰癕V1404”可以在器件庫里面找到，方法可以參考上面查找晶體管的方法。圖15 可變電容VC曲線測量 按并雙擊它，修改里面的項目，定義一個名為：“Vbias”的變量 修改電源的屬性，把Vdc改為“Vbias” 雙擊，并修改屬性，要求單點掃描頻率點2.3GHz，并計算“Z參數(shù)” 雙擊，并修改屬性，要求掃描變量“Vbias” ，選擇Simulatuion1“SP1” 按“F7”進(jìn)行電路仿真。 在“Date Display”按，并在對話框里編輯公式為： 按，并單擊“advance”選項，把“C_V

13、aractor”輸入對話框里面，點擊“確定”就可以顯示如圖16所示的曲線。圖16 VC曲線 按，同樣單擊單擊“advance”選項，把“C_Varactor”輸入對話框里面，點擊“確定”就可以顯示如圖17所示的表格。圖17利用該VC曲線，結(jié)合硅雙極管的管芯模型和封裝模型，按照典型值，利用等效諧振圖可以計算出該振蕩器的諧振頻率在反饋電感為0.2nH級這個數(shù)量級的時候，振蕩頻率為4.0GHz左右，考慮到該模型只有定性參考價值，所以確定該振蕩器結(jié)構(gòu)，并可以在仿真過程中，不斷的修改和優(yōu)化電路參數(shù)，使得振蕩器達(dá)到設(shè)計要求。5.4振蕩器瞬時仿真利用Transient Simulation仿真器可以做振蕩器

14、的瞬時仿真，看到實時波形。 新建一個電路原理圖文件 在這張電路原理圖中，按照上面的方法，建立如圖18所示的電路圖圖18振蕩器電路原理圖注意：記得要添加“Vout”這個節(jié)點名稱，還有假如器件找不到的，在器件庫里面查找，具體情況可以參考查找“晶體管”一節(jié)。 在“SimulationTransient”類里面找到瞬時仿真器，并雙擊修改里面的參數(shù)，如下圖19所示。其中“star time”表示開始仿真的時間；“stop time”表示結(jié)束仿真的時間，“MaxTimeStep”表示最大的抽樣時間，這里按照抽樣定理對最大的抽樣時間是有要求的，具體的算法和介紹可以參考ADS的幫助文檔，在文檔里面查找“Tra

15、nsient“就可以了。圖19 瞬時仿真器配置 按“F7”開始仿真 在出來的“Data Display”窗口里面，按，選擇“Vout”按確定，這樣就可以看到“Vout”點的瞬時波形，按，并“new”一個新的“Marker”，在“Vout”的瞬時波形圖中，點擊一下，然后移動鼠標(biāo)，把“marker”移動到需要的地方，就可以看到該點的具體數(shù)值。結(jié)果如下圖20所示。圖20 按，編輯公式：這表示要對“Vout”在“Marker”m1，m2之間進(jìn)行一個頻率變換，這樣出來的“Spectrum”就是m1和m2之間的頻譜。 按，在“advanced”里面加入“Spectrum”點擊“OK”就可以看到m1和m2之

16、間的頻譜分量，加入“marker”m3就可以知道振蕩器大概振蕩的頻率。如圖21所示。圖20 m1，m2之間的頻譜5.5振蕩器的諧波平衡仿真 新建一個電路原理圖或者就在“Transient仿真電路圖”里面，把電路原理圖改為如下圖21所示的電路圖圖21 諧波平衡仿真的電路圖這和瞬時仿真唯一不同的就是多加入了一個“OscPort”器件在反饋網(wǎng)絡(luò)和諧振網(wǎng)絡(luò)之間，這是諧波平衡法仿真相位噪音的需要，具體的情況可以參考ADS的幫助文檔，查找“OscPort”就可以看到很具體的幫助信息。其中“OscPort”是在類“Simulation-HB”里面。 在類“Simulation-HB”里面把仿真器拉出來，并雙

17、擊配置這個諧波平衡仿真器第一步：設(shè)置頻率和“Order”如下圖22所示圖22第二步設(shè)置參數(shù)，主要是把“OverSample”改為4，如下圖23所示圖23第三步：設(shè)置噪音計算，把最后一行的“Nonlinear noise”和“Oscillator”都選上，然后在“Noise frequency”里面選擇的掃描方式是“l(fā)og”相位噪音的計算從1Hz到10MHz，并把“FM noise”調(diào)頻噪音也計算出來，具體如下圖24所示。圖24第四步：“noise2設(shè)置”主要就是把“Vout”加進(jìn)去，并選擇“sort by value”具體見下圖圖25第四步：在“Osc”選項里面把Osc1加進(jìn)去，這就是我們加入

18、的那個OscPort類器件。圖26其他地方也不用修改了，最后就得到配置好的諧波平衡仿真器，見圖27圖27諧波平衡仿真器 按“F7”進(jìn)行仿真。 在“Data Display”窗口里面按照上面的方法，把需要的數(shù)據(jù)都顯示出來見下圖圖28 時域波形圖28是時域波形，注意是要加入“Eqn”的圖29諧波頻率和幅度 圖30相位噪音仿真結(jié)果這里的pnmx是相位噪音，單位為dBc/Hz；anmx是調(diào)幅噪音，單位為dBc/Hz；pnfm是附加相位噪音，單位為dBc/Hz。其中pnfm和anmx都是通過頻率靈敏度分析來獲得的，pnmx是通過混頻分析獲得的。具體分析，可以參考ADS幫助文檔，查找“pnmx”就可以。圖

19、31相位噪音的具體數(shù)值5.6振蕩器振蕩頻率線性度分析 把控制變?nèi)莨茈妷旱碾娫磳傩孕薷囊幌?，“Vdc”設(shè)置為變量“Vtune”，增加一個VAR變量“Vtune” 修改諧波平衡仿真器，這時不計算噪音，只是掃描變量“Vtune”，所以可以把最后一行的“Nonlinear noise”不給予選上。 建議把原來做過諧波平衡，分析相位噪音的諧波平衡仿真器去掉，在重新拉一個回來，這樣修改的項目就不多，下面以新來的諧波平衡仿真器為例，說明一下，現(xiàn)在這個諧波平衡仿真器應(yīng)該修改的地方。第一步：修改頻率圖32第二步：修改“Sweep”，這是說明掃描Vtune變量的具體情況的，參見圖33圖33第三步：加入“Osc1”

20、這和前面的一樣的，不再重復(fù)。 按“F7”進(jìn)行仿真 顯示仿真結(jié)果如下圖所示：圖33電壓頻率曲線圖34功率頻率曲線圖36頻率、諧波功率曲線6總結(jié)從最后的仿真結(jié)果可以看出，設(shè)計的任務(wù)還是完成了，因為ADS涉及的內(nèi)容太多了，所以建議大家都看看幫助，幫助里面的查找功能非常強大的，基本上在ADS上遇到的問題都可以從幫助里面找到答案，另外ADS器件庫的搜索功能除了慢點外，其他的也是挺好的，假如有什么器件一時找不到了，也建議使用器件庫來搜索。7 附錄Manuals Intro and Simulation Components Chapter 5: Simulation Control Items Print

21、 version of this Book (PDF file) Simulation Parameters: HB The tabs in the Harmonic Balance dialog box allow you to set the following parameters: Freq sets parameters related to the frequencies of fundamentals. Sweep sets parameters related to sweeps, and references sweep plans. Params sets status a

22、nd device operating point levels, as well as parameters related to FFT oversampling and convergence. Small-Sig sets parameters related to small-signal/large-signal simulation. Noise (1) sets parameters related to noise simulation, including sweeps. Input and output ports can be defined here. FM nois

23、e can be selected for oscillator simulations. Noise (2) selects nodes at which to calculate noise data, and sorts the noise contributors. Port noise options are provided here also. NoiseCons is used to specify which NoiseCon nonlinear noise controllers should be simulated, allowing more flexible noi

24、se simulations to be performed than Noise(1) and Noise(2) allow. Osc sets parameters related to oscillator simulation. Solver allows you to choose between a Direct or Krylov solver or to enable an automatic selection. Output allows you to selectively save your simulation data to a dataset. Display s

25、hows or hides parameters in the Schematic window. The available parameters and options are described in the following sections. Nodes for Calculation of Noise Parameters Use this area to select nodes at which you want linear noise data to be reported. Noise voltages and currents are reported in rms

26、units. Freq Fundamental Frequencies Maximum order is the maximum order of the intermodulation terms in the simulation. For example, assume there are two fundamentals and Order (see below) is 3. If Maximum order is 0 or 1, no mixing products are simulated. The frequency list consists of the fundament

27、al and the first, second, and third harmonics of each source. If Maximum order is 2, the sum and difference frequencies are added to the list. If Maximum order is 3, the second harmonic of one source can mix with the fundamental of the others, and so on. The combined order is the sum of the individu

28、al frequency orders that are added or subtracted to make up the frequency list. Frequency is the frequency of the fundamental(s). Order is the maximum order (harmonic number) of the fundamental(s) that will be considered. Select edits the fundamental frequencies and their orders (by double-clicking)

29、. Add adds a frequency and its associated fundamental and order. Cut deletes a frequency and its associated fundamental and order. Paste takes a frequency item that has been cut and places it in a different order in the Select window. Sweep Refer to Sweep. Params Budget Perform Budget simulation rep

30、orts current and voltage data into and out of devices following a simulation. Current into a device is identified as .device_name.t1.i, and out of that device as .device_name.t2.i. Voltage at the input to a device is identified as .device_name.t1.v, and at the output of that device as .device_name.t

31、2.v. Levels Refer to Levels. FFT Oversample sets the FFT oversampling ratio. Higher levels increase the accuracy of the solution by reducing the FFT aliasing error and improving convergence. Memory and speed are affected less when the direct harmonic balance method is used than when the Krylov optio

32、n is used. More brings up a small dialog box. To increase simulation accuracy, enter in the field an integer representing a ratio by which the simulator will oversample each fundamental. Convergence Auto mode automatically adjusts key convergence parameters and resimulates to achieve convergence. As

33、 it trades efficiency for ease of use, it is suited to beginning ADS users who are unfamiliar with the ADS parameters to control the convergence. Manual mode enables an advanced damped Newton solver. This solver guarantees a robust and steady march toward the solution with each harmonic balance iter

34、ation. The convergence rate is enhanced by its selection of a near-optimal damping constant, choice of several individual norms in the convergence checks, and control over the residual reduction threshold at each iteration. Max. iterations is the maximum number of iterations to be performed. The sim

35、ulation will iterate until it converges, an error occurs, or this limit is reached. Restart instructs the simulator not to use the last solution as the initial guess for the next solution. Use Initial Guess (Harmonic Balance) Check this box to save your initial guess to a dataset that can be referre

36、d to for a subsequent harmonic balance simulation, including circuit envelope.For example, if you have saved the HB solution, you can later do a nonlinear noise simulation and use this saved solution as the initial guess, removing the time required to recompute the nonlinear HB solution. Or you coul

37、d quickly get to the initial HB solution, and then sweep a parameter to see the changes. In this later case, you will probably either want to disable the Write Final Solution (see following topic), or use a different file for the final solution, to avoid over-writing the initial guess solution. If n

38、o file name is supplied, a default name is generated internally, using the design name and appending the suffix .hbs. A suffix is neither required nor added to any user supplied file name. The Annotate value specified in the DC Solutions tab in the Options block is also used to control the amount of

39、 annotation generated when there are topology changes detected during the reading of the initial guess file. Refer to the section DC Solutions. Since HB simulations also utilize the DC solution, to get optimum speed-up, both the DC solution and the HB solution should be saved and re-used as initial

40、guesses. The initial guess file does not need to contain all the HB frequencies. For example, one could do a one-tone simulation with just a very nonlinear LO, save that solution away and then use it as an initial guess in a two tone simulation. The exact frequencies do not have to match between the

41、 present analysis and the initial guess solution. However, the fundamental indexes should match. For example, a solution saved from a two tone analysis with Freq1 = 1GHz and Freq2 = 1kHz would not be a good match for a simulation with Freq1 = 1kHz and Freq2 = 1 GHz. If the simulator cannot converge

42、with the supplied initial guess, it then attempts to a global node-setting by connecting every node through a small resistor to an equivalent source. It then attempts to sweep this resistor value to a very large value and eventually tries to remove it. Final Solution (Harmonic Balance) Check this bo

43、x to save your final HB solution to the output file. If a filename is not supplied, a file name is internally generate using the design name, followed by an .hbs suffix. If a file name is supplied, the suffix is neither appended nor required. If this box is checked, then the last HB solution is put

44、out to the specified file. If this is the same file as that used for the Initial Guess, this file is updated with the latest solution. Transient simulations can also be programmed to generate a harmonic balance solution that can then be used as an initial guess for an HB simulation. Refer to the sec

45、tion, Compute HB Solution. Small-Sig This feature employs a large-signal/small-signal method to achieve much faster simulations when some signal sources (a) are much smaller than others, and (b) can be assumed not to exercise circuit nonlinearities. For example, in a mixer the LO tone could be consi

46、dered the large-signal source and the RF the small-signal source. To edit these parameters and request a small-signal analysis, click Small-signal at the bottom of the dialog box. Small-signal frequency Refer to Sweep. Use all small-signal frequencies solves for all small-signal mixer frequencies in

47、 both sidebands. This default option requires more memory and simulation time, but is required for the most accurate simulations. Merge small- and large-signal frequencies By default, the simulator reports only the small-signal upper and lower sideband frequencies in a mixer or oscillator simulation

48、. Selecting this option causes the fundamental frequencies to be restored to the dataset, and merges them sequentially. Noise (1) To edit these parameters and request a noise analysis, click Nonlinear noise at the bottom of the dialog box. Noise frequency Use this area to select the frequency(s) at

49、which nonlinear noise is computed. Sweep Type Refer to Sweep Type. Input Frequency Because the simulator uses a single-sideband definition of noise figure, the correct input sideband frequency must be specified here. This parameter identifies which input frequency will mix to the noise frequency of

50、interest. In the case of mixers, Input frequency is typically determined by an equation that involves the local oscillator (LO) frequency and the noise frequency. Either the sum of or difference between these two values is used, depending on whether upconversion or downconversion is taking place. Th

51、e above parameters do not need to be specified if only the output noise voltage is desired (that is, if no noise figure is computed). Noise input port is the number of the source port at which noise is injected. This is commonly the RF port. Although any valid port number can be used, the output por

52、t number is frequently defined as Num=1. Noise output port is the number of the Term component at which noise is retrieved. This is commonly the IF port. Although any valid port number can be used, the input port number is frequently defined as Num=2. Include FM noise (osc. only) causes an FM noise

53、analysis to be performed in addition to a mixing noise analysis for oscillator phase noise. This simulates a second model for phase noise, which may be more accurate at small offset frequencies. Noise (2) To edit these parameters and request a noise analysis, click Nonlinear noise at the bottom of t

54、he dialog box. Nodes for noise parameter calculation Use this area to select named nodes at which the simulator will compute noise. NoteThe fewer the number of nodes requested, the quicker the simulation and the less memory required. Edit selects the named node(s) for the simulator to consider. Sele

55、ct holds the names of the nodes the simulator will consider. Add adds a named node. Cut deletes a named node. Paste takes a named node that has been cut and places it in a different order in the Select window. Noise Contributors Use this area to sort contributions to noise, as well as a threshold be

56、low which noise will not be reported. Mode provides the following options: Off causes no individual noise contributors (nodes) to be selected. The result is simply a value for total noise at the node. Sort by value sorts individual noise contributors, from largest to smallest, that exceed a user-def

57、ined threshold (see below). The subcomponents of the nonlinear devices that generate noise (such as Rb, Rc, Re, Ib, and Ic in a BJT) are listed separately, as well as the total noise from the device. Sort by name causes individual noise contributors to be identified and sorts them alphabetically. The subcomponents of the nonlinear devices that generate noise (such as Rb, Rc, Re, Ib, and Ic in a BJT) are listed separately, as well as the total noise fr