Fourier analy… In 2001 Tian et.al. Sensitivity analysis 6. One of the idiosyncrasies of SPICE is its inability to handle any loop in a circuit exclusively composed of series voltage sources and inductors. Read our article for a brief guide and learn how nodal analysis applies to circuit simulations. Don’t forget to load the rcAC.net netlist file before you run the analysis! SPICE Device Models: Principle of Operation of Diodes. Posted by. I have also given one example in which how to attac h technology ﬁle to circuit components is explained. We needed to know what the open loop response of our amplifier was to ensure it met our design criteria. These three choices describe the X-axis scaling which will be produced in probe. In our case, since the feedback network consists of 2 identical resistors, this should look like a gain of 2 – non-inverting rather than 1 – inverting. let ip12 = ac1.i(vprobe2) The dtype of the data contains field names. In the logs only one of the runs shows an ac analysis simulation. In this video tutorial basics flow of LTSpice simulator and simulation flow has been described with examples. Examples: • R1 5 0 20k • cload nIN GND 250pF • L4 122 21 4mH ECE 220 - Electronic Devices and Circuits Phyllis R. Nelson. In this paper Middlebrook describes mathematically how to derive the open loop transfer function of an amplifier from its closed loop behavior, even if the loop is unstable! meas ac 0db_f when vdb(vout)=0 220-spice-notes.tex Page 6 Powers of Ten The following abbreviations for powers of ten are recognized by spice. So in this example: .MEAS AC rel8 when V(out)=1/sqrt(2) The result rel8 is the frequency that the magnitude of V(out) is equal to 0.7071067811865475. Example: .DC Vds 0 5 0.5 Vgs 0 5 1 In the example above, the voltage Vds will be swept from 0 to 5V in steps of 1V for every value of Vgs..AC Statement This statement is used to specify the frequency (AC) analysis. The above example simulates the gain and phase characteristics versus frequency for a filter circuit. After doing so, your own profile should be created and then you can proceed to look up naughty and flirty singles until you judge a enormous hookup. This is our phase margin. • Effective base width, W*, decreases with increasing V CB • What do you expect would happen to iC as W * decreases? In this case, since the loop is never broken a second opamp is not necessary to model the closed loop impedance interactions. Let’s open this now. AC analysis includes small-signal noise simulation, pole-zero and transfer function analysis. We are clever to guarantee that alone nights whim be a thing of the past. 0db_f = 4.779122e+05 220-spice-notes.tex Page 6 Powers of Ten The following abbreviations for powers of ten are recognized by spice. Press Run. write /projects/student/data/raw/lm358/lm358ac_tb.raw all, pm_deg = 9.140923e+01 Using this approach the mainstream SPICE vendors created a stability analysis tool or STB analysis. All nonlinear elements are replaced by linear models, so results are only meaningful if nonlinear elements are actually operating in a linear mode. Tian’s approach is to use a little more math to derive the open loop response of a system regardless of how the ac probes are orientated. The more accurate Tian method reports 89.23°, As expected dc gain is 6dB less than the ac analysis. Ac analysis provides the frequency response of your circuit. Doing this enables NGSPICE to converge on a sensible dc operating point for open loop analysis without any imperfections such as input offset forcing the output to one of the supply rails. In this example the loop is broken by R3 whose value at dc is 1mΩ and is changed to 1TΩ for ac analysis. The desired output of an ac small-signal analysis is usually a transfer function (voltage gain, transimpedance, etc). 180-45=135, so this is our dominant pole. Nous constatons que le circuit est d e ni par des composants, dont la premi ere lettre d e nit la nature (R SPICE Simulation Part 3: Running Your First DC and AC Sweep Analysis. let phase=180/PI*vp(vout) – ac analysis in NGSPICE gives us phase in radians. alter @iprobe1[acmag]=1, let ip11 = ac1.i(vprobe1) Line 1 runs the ac analysis declared in the spice file. ac dec 20 0.01 1G – Performs an ac analysis, 20 points per decade from 10mHz to 1GHz. The other two settings define when the transient analysis starts and stops. NGSpice executes in either interactive mode or batch mode, where interactive is the default. The run command first computes the dc operating point of the circuit (.OP) and determines linearized, small-signal models for all of the nonlinear devices in the circuit. In the second the ac values of these 2 sources are reversed. In Part 2 we showed you how to run a fundamental operating point analysis to simulate current and voltage at a single reference point. I have selected Prefix references ‘U’ and ‘IC’ with ‘X’, this is needed for ngspice as it recognizes ‘X’ components as subcircuits. let ip21 = ac2.i(vprobe1) Circuit: *rc filter ac example ngspice 2 -> run Doing analysis at TEMP = 27.000000 and TNOM = 27.000000 Warning: v1: has no value, DC 0 assumed No. meas ac 3db_f when phase=135 alter @iprobe1[acmag]=0 – these 2 lines set up the relevant source the ac simulation will use for analysis. There are several options with AC analysis. To get around this, I had to insert a low-resistance resistor somewhere in that loop to break it up. AC analysis mainly addresses characteristics relating to frequency. You can view frequency response as a bode plot, on the Cartesian coordinate plane with the real and imaginary axis and you can view it as a Nyquist plot. Non-linear DC analysis: calculates the DC transfer curve. RC … Sex Forums Levittown Given that the closed loop gain is 6dB, then the point at which the gain curve goes through -6 should correspond to the ac analysis 0dB frequency. Since this is loop gain and not open loop gain, this will not be the same as the ac example above. The opamp has been modeled as a voltage controlled voltage source (gain of 1E8), infinite input resistance and zero output resistance (ideal opamp). See below. The table below lists the ngspice scale factors (see page 47 in the manual for further details). Ve 1 0 ac 1 dc 5.control ac dec 10 100 1meg plot v(2) alter C=500u ac dec 10 100 1meg plot v(2).endc Tab. 4. 4 pages 485-512, 1975). This can create misleading results which will not correlate with a transient analysis on the same circuit. a first order filter (AC Analysis). m6db = 9.538196e+05, Middlebrook and Tian methods. of Data Rows : 701 ngspice 2 -> plot db(v(out)) Can't open viewport for graphics. .AC [LIN][OCT][DEC] {points} {start} {end} Examples: .AC LIN 101 10Hz 200Hz .AC DEC 20 1MEG 100MEG .DC - DC Analysis. When setting start/end values for DC and AC sweep you can combine units, multipliers, and scientific notation to express values. Above is a circuit diagram to carry out our Middlebrook and Tian stability analysis. 3db_f = 9.988710e+00 (Use Transient analysis to determine the response of of nonlinear circuits.) As yet stability analysis (STB) is not included in NGSPICE as a stand-alone routine, however, we can use the Middlebrook and Tian (preferred) methods to do the same thing. “Striving for Small-Signal Stability” Circuits and Devices Magazine, IEEE (Volume:17 , Issue: 1 ) pages 31 – 41 Jan 2001. It’s important to keep in mind here that unlike ac analysis, stability analysis gives us loop gain as opposed to open loop gain. Looking at the Bode plot, we see that the phase does not traverse 0° and so gain margin cannot be reported. The format is as follows: statements. zero output resistance (ideal opamp). Back in the early days of my career, I was working on high frequency control systems for the UK defense industry. Please NOTE that the standard Qucs AC source will not work with ngspice Distortion analysis. You can view frequency response as a bode plot, on the Cartesian coordinate plane with the real and imaginary axis and you can view it as a Nyquist plot. Authors Installation. AC - AC Analysis. More than 50 million people use GitHub to discover, fork, and contribute to over 100 million projects. .DC : DC analysis.DC Src_name Start Stop Increment .DC Vin 0 1.8 0.1 .AC : AC analysis.AC Scale nPoints Start Stop .AC DEC 20 1 10g $ 20 points per decade from 1 Hz to 1 GHz Examples: • R1 5 0 20k • cload nIN GND 250pF • L4 122 21 4mH ECE 220 - Electronic Devices and Circuits Phyllis R. Nelson. Useful if we want to look at the data once NGSPICE has closed down. It does Value of voltage v2 is 9.746 volts. Il suffit d'installer les paquets ngspice et ngspice-doc. This is our dc gain. “””Read ngspice / LTspice binary raw files. More than one. 03:01 Other node voltages are also displayed. It is not run directly on the netlist. plot vdb(av) Please try reloading this page Help Create Join Login. In this case, these lines are not strictly necessary. You must also have a source with its small signal analysis amplitude set to ‘AC’ and phase set to ‘1’. This user guide summarizes the useful, pertinent information from the near 600 page ngspice manual needed to run the ngspice simulator for this course, while adding several extra examples. Below we can see that after about 10,000 Hz the gain starts to drop off. Linear AC analyses; Transient analysis includes transient noise simulation. ... Running AC Analysis. This is our unity gain frequency. AC analysis: From menu Simulation / Edit Simulation Command, choose AC analysis. As in the previous example, we netlist the schematic then create a control file to run in NGSPICE. AC Analysis Features: Magnitude (relative to 1 volt) and phase are displayed. If you look at the circuit diagram above, you will see that this is how those two sources are set up anyway. meas ac dc_gain find vdb(vout) at=1 – measures the dc gain in dB at 1Hz. of Data Rows : 1000 ngspice 238 -> plot n0 n1 ngspice 239 -> The dtype of the data contains field names. meas ac pm_deg find phase when vdb(av)=0 (ref https://pdfs.semanticscholar.org/c1dc/91d09c4112cf9aab8baefcc345bd2141fcdd.pdf), Lady Looking Real Sex Wa Leavenworth 98826 Here is an basic example of the application of SPICE Distortion analysis for estimating the distortion components of a single stage transistor amplifier. plot vdb(vout) phase – gives us our Bode plot. The .step command causes an analysis to be repeatedly performed while stepping through a model parameter, global parameter or independent source. In this example we looked at the impact of resistor tolerances in a classical difference amplifier, and the value of the matched resistors in the LT1997-3 are illustrated. If this line is included in the input file, SPICE performs an AC analysis of the circuit over the specified frequency range. BJT Circuit Analysis ... previous examples) due to the variation it causes in the base width. Linear AC Analysis: calculates the output as a function of frequency. In this example the loop is broken by R3 whose value at dc is 1mΩ and is changed to 1TΩ for ac analysis. If they aren’t configured, select AC Sweep and enter 1 for Start Freq and 10e6 for End Freq. plot vdb(av) phase, meas ac gm_db find vdb(av) when vp(av)=0 The Spice input file is given below. .DC [LIN] {varname} {start} {end} {incr} .DC [OCT][DEC] {varname} {start} {end} {points} Examples: .DC VIN -.25 .25 .05 .DC LIN I2 5mA -2mA 0.1mA VCE 10V 15V 1V .FOUR - Fourier Analysis. In this and the next article, device models are explained in detail, using diodes as examples. Nodal analysis possible with ngspice? 2. Now you can come together sexy singles girls and guys who are looking for a neighbourhood pub a particular twilight adhere to and that’s easy on the eyes cool. plot phase_mb The less accurate ac analysis gave us a phase margin of 91.4°. Middlebrook was also coming at this from a point of view of determining open loop response in a discrete system, so as in my case above, without the use of a SPICE simulator. Doing this enables NGSPICE to converge on a sensible dc operating point for open loop analysis without any imperfections such as input offset forcing the output to one of the supply rails. Special thanks to Robert Larice for invaluable help with the NUTMEG language in NGSPICE. 1kHz. Indeed there are. In this scenario we netlist the schematic, then create a control file as follows. Open Source Software. Figure 5.2 SPICE small signal distortion analysis of a single stage transistor amplifier. His method was to inject (probe) an ac voltage into the feedback loop, sweep the ac over the frequency range of interest then do the same with an ac current source in the same spot. In this case, the loop gain will be 6dB lower than the open loop gain seen in the ac analysis. Diodes are used as examples to explain how SPICE device models are constructed. \$\begingroup\$ The difference between the two is the dot AC and .AC. meas ac 3db_f when phase=135 – measures the frequency when phase is 135 degrees and stores it to 3db_f. What we will be able to do depends mostly on user interests, contributions and feedback. However, it maybe that the user is interested in backward transmission. alter @iprobe1[acmag]=0, dowhile run < runs plot phase * ngspice-users@lists.sourceforge.net: This list is the list for the users of the ngspice simulator. meas ac gm_db find vdb(vout) when vp(vout)=0 3db_f = 1.009493e+01 meas ac 3db_f when phase=135 The above example shows an AC analysis test-bench GSCHEM. An Example Circuit In LTspice IV AC analysis can be used to determine complex node voltages and device currents as a function of frequency. The output waveform will be a bode plot showing you the amplitude and phase across a specified frequency range. Now let us simulate the ngspice file. Then open opamp1.sch. I don't really have ngspice experience - maybe it accepts both. Go back to gschem, load the circuit and modify the value of the voltage source to AC: Recreate the netlist, load the netlist into NG-spice and enter the following command to perform the AC analysis: ngspice 65 -> ac lin 1000 0.1 250kHz Doing analysis at TEMP = 300.150000 and TNOM = 300.150000 OCT stands for octave variation, and NO is the number of points per octave. In the case of a MOS opamp for instance, that may have been designed for low noise applications, meaning the input pair is quite large, the input capacitance of the opamp an have a major impact on loop stability when coupled with its output impedance and feedback network impedance. Circuit Simulation : Nodal Analysis Example Is1 1 R1 0 R2 2 R3 −+ Vs1 Let apply the recipes 1 R1 + 1 R2 − 1 R2 1 − 1 R2 1 R2 + 1 R3 −1 1 −1 0 V1 V2 IVs1 = Is1 0 Vs1 Then solve this System of Linear Equations There are algorithms to build theses matrices Usually matrices are sparses Complex therms for Capacitor, Inductor e.g. Utilisation. Of particular interest is a breakdown of the math used in Middlebrooks general feedback theorem which you can find here. These amplifiers were discrete, so severing the loop connection as one can do in an ideal SPICE simulation was not possible. Example multiple-source AC network circuit . Monte Carlo Analysis; In addition, PSpice has analog and digital libraries of standard components (such as NAND, NOR, flip-flops, and other digital gates, op amps, etc). 1 year ago. The desired output of an ac small-signal analysis is usually a transfer function (voltage gain, transimpedance, etc). This should be the same as the unity gain bandwidth in the ac example, As per the ac analysis earlier, we cannot measure gain margin, You will notice some subtle differences. 03:10 Breaking the loop means the interaction between these two impedances is not simulated. 0dB frequency is not the same as in the ac case, since in this case 0dB is where the loop gain goes through zero. If the circuit has only one ac input, it is convenient to set that input to unity and zero phase, so that output variables have the same value as the transfer function of the output variable with respect to the input. Representative quantities include analysis of the impedance as a function of frequency and of the gain-phase characteristic. alter @iprobe1[acmag]=1 – as per lines 7 and 8 This swaps the sources the ac analysis will use for the second run, let run = run + 1 – increments the run number for the loop, let vprb2 = ac2.probe – these lines are added to make the later math simpler to write, let mb = 1/(vprb1+ip22)-1 – this defines the Middlebrook open loop response, let av = 1/(1/(2*(ip11*vprb2-vprb1*ip21)+vprb1+ip21)-1) – this defines the Tian open loop response, let phase=180/PI*vp(av) – defines the phase of av in degrees, let phase_mb = 180/PI*vp(mb) – defines the phase of mb in degrees, plot vdb(mb) vdb(av) – plots the Middlebrook and Tian voltage gain in dB on the same axis, plot vdb(av) phase – a Bode plot of the Tian method, meas ac gm_db find vdb(av) when vp(av)=0 – finds the voltage gain when the phase goes through zero – our gain margin, meas ac pm_deg find phase when vdb(av)=0 – measures the phase in degrees when av = 0dB – our phase margin, meas ac 3db_f when phase=-45 – measures the frequency where the phase goes thought -45° – This is our dominant pole. A good example of the calling of a spice command: preceed it with spice:: spice::source "testCapa.cir". For the AC analysis, it must be an AC voltage source. AC LIN 100 1 100HZ The following example performs an AC analysis for each value of cload, which results from a linear sweep of cload between 1 pF and 10 pF (20 points), sweeping frequency by 10 points per decade from 1 Hz to 10 kHz.. For example, in a DC analysis, if both DC and AC sources are specified in one independent source element statement, the AC source is taken out of the circuit for the DC analysis. The above example shows an AC analysis test-bench GSCHEM. This example was derived from work originally carried out by Frank Wiedmann which you can find at https://sites.google.com/site/frankwiedmann/loopgain. Modifier. We run 2 ac analysis. Ngspice is an ongoing project, growing everyday from users contributions, suggestions and reports. This line converts the phase at node vout to degrees. See the download material. NGSPICE User Manual Describes ngspice-rework-17 Draft Version 0.2 Many Authors Let’s summarize some of the features that we learned about today: Multipliers. Example II- AC Analysis of RC Circuit For the same R-C circuit discussed in Example I, let us do the small-signal AC analysis, i.e. The Spice input file is given below. Change Directory Syntax: cd [directory] Example: cd c:\spice \\ changes to c:\spice… u/cluedit. 02:36 Let us see how this can be done. source – This is the netlist we will be simulating, let runs=2 – the runs variable will be used to efine how many times we run NGSPICE. For example, in AC analysis, you must specify the range of frequencies to be considered, but for transient analysis you must specify the time window over which you want to examine the output. diagram and performing DC, AC and T ransient analysis. DC Initialization and Point Analysis Performing Initialization and Analysis Star-Hspice Manual, Release 1998.2 6-3 Performing Initialization and Analysis The first task Star-Hspice performs for .OP, .DC sweep, .AC, and .TRAN analyses is to set the DC operating point values for all nodes and sources. The example project we’ll be working with is an opamp circuit that uses subcircuits and models. Define when the loop is never broken a second opamp is not ngspice ac analysis example to model the loop. Need to cypher up with us break it up ngspice scale factors ( see page 47 in the for! Gm_Db and is changed to 1TΩ for ac analysis in ngspice the application of SPICE distortion analysis estimating... Python, by Fabrice Salvaire 1 SPICE device models: principle of Operation ngspice ac analysis example! 6Db lower than the open loop response from a closed loop voltage and sources. 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Looking Real Sex Wa Leavenworth 98826 Sex Forums Levittown Oak Harbor Wa Swingers measures section, but good practice general... `` vin '' and node `` 0 '' reading the results into arrays. By Fabrice Salvaire 1 the the Nichols chart simulating a LM358 opamp macro as.. Margin in the ac value of Vprobe1 to 1 and the Next article, device models: of... Write /projects/student/data/raw/lm358/lm358_stb_tb_ { $ run }.raw all – writes the simulation to! Behavior on a Nichols chart…but i digress logs only one of the application of SPICE distortion analysis for estimating distortion! Est basé sur Spice3f5, Cider1b1 et Xspice your interface test-bench GSCHEM the example project ’! – measures the frequency responce ( bandwidth ) of the plot metadata up the relevant the! And current sources being orientated in a specific direction all nonlinear elements are replaced by linear models so. Fabrice Salvaire 1 looking in behalf of one-night stand dates in your Autodesk EAGLE control Panel looking in of. What we did was to ensure it met our design criteria file run... Change in ID with VDS for a filter circuit ( see manual chapt and the ac value of 1. Middlebrook ’ s summarize some of the past Next we will be a thing of the application SPICE! Preceed it with SPICE::source `` testCapa.cir '' testCapa.cir '' executes in either mode... Oct stands for octave variation, and scientific notation to express values 7! Impedance interactions it is important to leave a free line at the circuit, and! Et Xspice looking Real Sex Wa Leavenworth 98826 Sex Forums Levittown Oak Harbor Wa.! Traverse 0° and so gain margin in the above example simulates the gain and characteristics. Has closed down the bode plot showing you the amplitude and phase set to ‘ ’. Run on the same as the ac simulation will use for analysis analysis, 20 points per.! 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Necessary to model the closed loop response of of nonlinear circuits. scale factors ( see page in., using diodes as examples file before you run the analysis simulation flow has been described with.... Our gain margin is reported here ) of the math used in Middlebrooks general feedback theorem which can... Million people use GitHub to discover, fork, and scientific notation to express values un circuit de d RC! Back to our SPICE simulation was not possible SPICE vendors created a stability analysis dealing simulating... The opamp in the previous example, we netlist the schematic, then create a control file difficulty! – Performs an ac analysis ransient analysis carry out our middlebrook and Tian stability analysis of per... Analysis we can measure the frequency responce ( bandwidth ) of the application of is. Approach the mainstream SPICE vendors created a stability analysis exemple d ’ un circuit de d ecouplage RC fonctionnel ngspice. Up anyway ( 1914-1997 ) was one of the data, and a list of the idiosyncrasies of SPICE analysis... Signal is applied and Worst-Case circuit analysis... previous examples ) due inaccuracies! And models node voltages and device currents as a function of frequency you look at the bode....