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patrick

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  1. patrick

    تحلیل نویز در Hspice

    تحلیل نویز در Hspice NOISE ANALYSIS - RESISTOR EXAMPLE CIRCUIT RES_NOISE.CR Download the SPICE file You can't figure it out. You've taken one hundred samples of a 2.5V reference using a 16-bit ADC, but rarely are two consecutive readings the same. Okay, it's got to be noise, but where is it coming from? Unfortunately, one of our basic building blocks - the resistor - comes with its own inherent noise generator. But once we understand a little about the nature of this noise source, we have a few choices regarding how to reduce it. RESISTOR NOISE How is resistor noise modeled? Typically as a noise voltage in series with the resistor. POWER SPECTRAL DENSITY The Power Spectral Density simply describes how much noise power would generated by a resistor in a 1 Hz bandwidth. S = 4 k T R (V2/Hz) where S = the noise Power Spectral Density k = Boltzmans constant (1.38∙10-23) T = temperature in Kelvin (Room temp = 27 °C = 300 K) R = resistance This noise power is the same at all frequencies - commonly called white noise! NOTE! If you want to reduce the total noise in your circuit, then reduce your bandwidth! VOLTAGE SPECTRAL DENSITY The Voltage Spectral Density is simply the square root of the power spectral density. N = ( 4 k T R )½ (V / Hz½) Many manufacturers will specify the noise of their components (opamps for example) using these units. Notice the noise voltage units has the funky units of Volts per square root of the bandwidth. Later you'll see how to use N to calculate the RMS noise voltage in a circuit. RESISTOR NOISE EXAMPLE For a 100 kΩ resistor, let's find its power spectral density S = 4 k T R = 4 ∙1.38∙10-23 ∙ 300 ∙ 100k = 1.66∙10-15 ( V2 / Hz ) and voltage spectral density N = S ½ = (4 k T R) ½ = 40.7 ∙10-9 ( V / Hz½ ) (At first, 40 nV/Hz½ doesn't sound like much. But suppose your designing a low-noise design amplifier using a quiet op amp with an input voltage noise of only 4 nV/Hz½ . You wouldn't want to kill the party by using a 100k boom box as a feedback resistor. Smaller R values around 1k would be a better choice.) CIRCUIT NOISE How much noise will various resistors contribute at the output of your circuit? Four easy steps gets you the answer. Let's walk through an example. Our circuit above is a simple resistor divider (Gain = 1/2) followed by an amplifier (Gain = 1) and a low-pass filter (fc = 1MHz). Let's assume we're seeking the noise density at low frequencies where the low-pass filter has no effect. Step 1: Calculate S, the power spectral density from R1=100k. S = 4 k T R = 1.66∙10-15 ( V2 / Hz ) Step 2: Find A, the voltage gain A from the noise source to the output A = R2/(R1+R2) = 1/2 then use A to calculate the output power spectral density from R1. (Notice A2 is actually used because we are dealing with power here.) So = S ∙ A2 = 1.66∙10-15 ∙ (1/2)2 = 4.14 ∙10-16 (V2 / Hz) Step 3. Repeat for all noise sources. For R2=100k, we get the same answer as R1 So = S ∙ A2 = 1.66∙10-15 ∙ (1/2)2 = 4.14 ∙10-16 (V2 / Hz) For RLP1=100, we get So = S ∙ A2 = 1.66∙10-18 ∙ 1 = 1.66∙10-18 (V2 / Hz) Step 4: Adding the contributions from all resistors we get a total power spectral density of STOT = 4.14 ∙10-16 + 4.14 ∙10-16 + 1.66∙10-18 = 8.30 ∙10-16 (V2 / Hz) Now take the square root to get the total voltage spectral density of NTOT = STOT ½ = ( 8.30 ∙10-16 ) ½ = 2.88 ∙10-8 ( V / Hz½ ) There you have it! At low frequencies, your resistors contribute a total of 28.8 nV/ Hz½ at the circuit's output. WARNING!!! In this simple example, the gain (A) was found at low frequencies where the gain was flat. However, at higher frequencies, the low-pass filter rolls off the response. Real circuits include filters and amplifiers with gains that vary with frequency. Consequently, the noise calculations need to include these frequency effects! Sound fascinating? Yes! Sound like a pain in the can? Yes, again! Luckily, SPICE is equipped with the noise analysis tools. SPICE NOISE ANALYSIS The Noise Analysis essentially does the work in the above example for you. SPICE performs Noise Analysis together with an AC Analysis statement. For example, the statement .NOISE V(4) V1 5 asks SPICE to calculate the equivalent noise at both output V(4) and V1 at every 5th frequency point in the AC analysis. 1. Calculate the power spectral density S from EACH resistor to output node V(4). This is performed at every 5th frequency point specified in the AC analysis. 2. Add noise contributions from all resistors to find the total power spectral density S and total voltage spectral density N at node 4. 3. Calculate the transfer function V(4) / V1 to determine the total voltage spectral density N referred to the input source V1. CIRCUIT INSIGHT Simulate the SPICE file RES_NOISE.CIR. To recap, this circuit implements a simple resistor divider (Gain = 1/2) followed by an amplifier (Gain = 1) with a low-pass filter (fc = 1MHz). Open the output file RES_NOISE.OUT to view the noise results. For every 5 th frequency of the AC analysis (100, 1000, 10000, ... Hz), SPICE prints out a nice noise summary. At 100 Hz for example, we see the power spectral density from each resistor R1, R2 and RLP1. Do the results match the densities calculated above? How about the total power and voltage spectral density, does it match our numbers above? Seeing the noise from every resistor gives you some incredible insight! Why? It tells you who are the major contributors! Knowing the biggest noise makers, you can plan some noise reduction strategies - typically reducing bandwidth or resistor values. HANDS-ON DESIGN Try lowering the resistors to values like R1 = R2 = 1 kΩ. What is the effect on total noise? Increase the gain of amplifier in the EAMP statement. How does it effect noise? What have you noticed about the noise spectral density at high frequency? The noise begins to drop thanks to the low-pass filter RLP1 and CLP1. This could be a good thing! But of course, here's another one of life's balancing acts. Small bandwidth is good for low-noise, but not if it cuts into your signal's bandwidth! Cool Feature SPICE let's you plot the total voltage spectral density N at the output V(4) or the input V1. Just add trace ONOISE or INOISE to the plot window. You can even add these variables to a .PRINT statement! RMS VOLTAGE CALCULATION Okay, enough noise versus frequency! What is the total RMS noise voltage in my circuit? You calculate this by multiplying the noise power density S by the bandwidth Δf, then taking the square root. For a flat bandwidth. P = S ∙ Δf (V2) E = ( P ) ½ (VRMS) For a noise response that varies across the frequency spectrum, simply sum the noise power S at a number of frequency points fn = f1, f2, f3, ... P = ∑ Sn ∙ Δfn (V2) E = ( P ) ½ (VRMS) where Sn is the power density at fn and Δfn = fn+1 - fn . How do you pick the number of frequency points. If the noise changes slowly versus frequency, you probably don't need many points. On the other hand, a rapidly changing noise vs. f requires more points effectively sample the spectrum. If the noise is given in terms of the noise voltage density N, then the RMS voltage is calculated as E = ( ∑ Nn2 ∙ Δfn) ½ ( VRMS ) Cool Feature You can implement this last equation in many SPICE simulators. Recalling that ONOISE represents the voltage spectral density N, simply add the following equation to the plot window. In PSPICE, this looks like SQRT(SUM(ONOISE*ONOISE)) The far right of the graph shows the total RMS voltage of your circuit. (NOTE: You might have noticed that the frequency Δfn is absent from the equation above. Actually, the SUM function automatically calculates the Δfn term.) CIRCUIT INSIGHT Simulate the SPICE file RES_NOISE.CIR with an EAMP gain =1, R1 = R2 = 100k, RLP1 = 100 and CLP1 = 1.59 nF. This time add the trace ONOISE to a plot window. Now, open a new plot window and add the trace SQRT(SUM(ONOISE*ONOISE)). What is the total RMS noise voltage at the highest frequency point of the graph? HANDS-ON DESIGN You can experiment with values of R1, R2 and the low-pass filter to see the effect on RMS noise. Try increasing CLP1 do decrease the bandwidth. How does the bandwidth effect the total RMS noise? Did it go down with a smaller bandwidth as expected? FINAL NOTE Noise can be one of the more challenging and tougher design topics! Sometimes it takes a few trips around the block before it begins to make sense. Here are some helpful guides. SPICE, A Guide to Circuit Simulation and Analysis Using PSPICE, P. Tuinenga, Prentice-Hall. Low-Noise Electronic System Design, C. Motchenbacher and J. Connelly, John-Wiley and Sons, 1993. Analysis and Design of Integrated Circuits, P. Gray and R. Meyer, John-Wiley and Sons, 1993. SPICE FILE Download the file or copy this netlist into a text file with the *.cir extension. RES_NOISE.CIR - NOISE ANALYSIS: RESISTOR DIVIDER, AMP, AND LP FILTER * * RESISTOR DIVIDER V1 1 0 AC 1 DC 5 R1 1 2 100K R2 2 0 100K * * AMP AND LP FILTER EAMP 3 0 2 0 1 RLP1 3 4 100 CLP1 4 0 1.59NF * .AC DEC 5 100 100MEG .NOISE V(4) V1 5 .PRINT NOISE ONOISE .PROBE .END منبع
  2. patrick

    Hspice Differential IO Kit User’s Manual

    [h=2]Hspice Differential IO Kit User’s Manual[/h] دانلود کنید [Hidden Content]
  3. patrick

    HSPICE Viewer User’s Guide

    [h=2]HSPICE Viewer User’s Guide[/h] دانلود کنید [Hidden Content] منبع
  4. [h=2]How do I create eye diagrams with Star-Hspice?[/h] A: Here is an example of an eye diagram circuit in the Star-Hspice distribution: /demo/awaves/demo/eyediag* As a quick reference, an eye diagram simply imitates the behavior of an oscilloscope (the waveform is displayed starting from the left end of the window and moving to the right at a given rate). When the electron beam reaches the right end of the window, it is moved quickly to the left end of the window where another "cycle" can be displayed. This type of display is quite useful in observing cyclic patterns that vary slightly from one cycle to another. To get these results in Star-Hspice, you need to include these two statements in your netlist: .PARAM width=5ns phase=0ns .PROBE TRAN TIME2=par('TIME+phase-int((TIME+phase)/width)*width') This creates a new TIME2 output variable. You may adjust the width of the window (in ns) with the parameter "width". You may also adjust the phase of the waveform with the parameter "phase." To get these results in AvanWaves: Open the resulting .tr# file In the "Results Browser" window, under "Types:" select "Params" Under "Curves:" select "time2" Under "Current X-Axis," click on "Apply" Under "Types:" again, select "Voltages," "Currents" or any other type of output variable you want to display Double click on the desired signals you want to display In the viewing window, click on the right mouse button; select "Monotonic Plot ..." منبع
  5. سلام من فردا امتحان دارم و استادمون 5 تا سوال بی جواب رو بهمون داده و گفته اینا سوالای امتحانه. لطف کنید و کمکم کنید جواباشو پیدا کنم. ازتون خواهش میکنم _________________________ 1-اگر فشار وارده بر جیوه در 273k از صفر تا 10 به توان 7 kg/m2 افزایش یابد،کار انجام شده را محاسبه کنید.میدانیم که حجم متوسط یک مول جیوه 1/47 *10به توان -5 و ضریب تراکم آن 3/84*10 به توان -11 می باشد. B=-1/7 2-در مورد درستی و نادرستی جملات زیر بحث کنید. الف) تغییر آنتلاپی یک سیستم بسته که در فشار ثابت تحول میابد برابر است با گرمای تبادل شده بین آن سیستم و محیط ب) در تحول برگشت پذیر تغییر آنتروپی سیستم چقدر است؟ ج)تغییر آنتروپی یک سیستم ایزوله همیشه مثبت یا صفر است. د) تغییر آنتالپی یک سیستم گاز کامل به فشار و حجم بستگی ندارد 3-یک موتور گرمایی رورسیبل طی یک سیکل یک مقداری گرما از یک منبع گرم میگیرد و مقدار w کار انجام میدهد و یک مقدار گرما به منبع سرد برمیگرداند.اگر دمای منبع گرم T1 و منبع سرد T2 باشد و ظرفیت گرامیی آن ها c1 و c2 باشد دمای نهایی سیستم و ماکزیسم مقدار کاری که میتوان از این سیستم به دست آورد را محاسبه کنید. 4-در داخل محفظه ای ایزوله 143/6 گرم آب در دمای 10c با 18گرم یخ در دمای 0c قرار دارد.اگر حالت نهایی سیستم (حالت تعادل) ، دمای صفر درجه سانتیگراد باشد ، تغییر آنتروپی سیستم را محاسبه کنید و نتیجه را بیان کنید. cp اب=18cal/mol Lf یخ=1436 cal/mol 5-یک کیلوگرم مذاب فلز A با دمای 1000k و یک کیلوگرم مذاب فلز ! با دمای 800k را مخلوط میکنیم.اگر ظرفیت حرارتی مذاب A در فشار ثابت 200ژول بر کیلوگرم باشد تغییر آنتروپی ناشی از این اختلاط چند ژول است؟ _________________________________________ ممنونم. قبولیه من بسته به این 5 تا سواله فرداست. تورو خدا کمک کنید
  6. رد پایت هنوز هم در لابلای برف های دل یخ زده ام پیداست طوری که اگر کسی روزی قصد دخول به دل را کند متوجه میشود که قبلتر نیز سکنه داشته
  7. ز ایران چنان بخت برگشته بود که حسین تهی هم 2 تن کشته بود
  8. بازی میکنی با قلبی که یک عمر است بازیچه است. چه تفاوتی میان کودک با تو و اسباب بازی با قلب من است؟
  9. patrick

    مشاعره

    دوش وقت سحر از قصه نجاتم دادند واندر ان ظلمت شب آب حیاتم دادند
  10. patrick

    نـامـه هـای خـط خطـی...!

    بودنت در کنارم خلیج پارس است و نبودنت دریای شمال. مانند خلیج باش.با شکوه و ارام
  11. در بعضی جهات آمریکا در بعضی جهات روسیه البته بخاطر اینکه اقتصاد روسیه با آمریکا قابل مقایسه نیست باید بگوییم آمریکا و سپس روسیه
  12. patrick

    نظر شما چیه ؟

    با هرکسی باید مثل خودش صحبت کرد. یه جور انعطاف پذیری لازم هست
  13. patrick

    مشاعره

    نگشت آسایشم یک لحظه دمساز گهی از گربه ترسیدم گه از باز
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