Archived. Abode plot is generated. find the frequency response of the magnitude and phase of a transfer function. What we did was to use a Nichols Chart in reverse. In the logs only one of the runs shows an ac analysis simulation. diagram and performing DC, AC and T ransient analysis. The gain is voltage dB. 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. As in the previous example, we netlist the schematic then create a control file to run in NGSPICE. Linear AC Analysis: calculates the output as a function of frequency. SPICE Simulations: DC Analysis, AC Analysis, Transient Analysis. In this case, the loop gain will be 6dB lower than the open loop gain seen in the ac analysis. In Part 2 we showed you how to run a fundamental operating point analysis to simulate current and voltage at a single reference point. plot vdb(mb) In 1975 Dr R. David Middlebrook (1929 – 2010) published his seminal paper “Measurement of Loop Gain in Feedback Systems” (International Journal of Electronics, Vol 38, No. 220-spice-notes.tex Page 6 Powers of Ten The following abbreviations for powers of ten are recognized by spice. plot vdb(vout) phase – gives us our Bode plot. meas ac 0db_f when vdb(vout)=0 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. AC analysis mainly addresses characteristics relating to frequency. AC Analysis Features: Magnitude (relative to 1 volt) and phase are displayed. These amplifiers were discrete, so severing the loop connection as one can do in an ideal SPICE simulation was not possible. Il est basé sur Spice3f5, Cider1b1 et Xspice. plot vdb(av) Here is an basic example of the application of SPICE Distortion analysis for estimating the distortion components of a single stage transistor amplifier. This is a video that demonstrates circuit simulation through ngspice with a simple circuit with single voltage source and a 10 ohms resister. In this case, since the loop is never broken a second opamp is not necessary to model the closed loop impedance interactions. AC Sweep should already be selected with specific values entered for Start Freq and End Freq. What we will be able to do depends mostly on user interests, contributions and feedback. 2. m6db = 9.538196e+05, Middlebrook and Tian methods. OCT stands for octave variation, and NO is the number of points per octave. Of particular interest is a breakdown of the math used in Middlebrooks general feedback theorem which you can find here. meas ac dc_gain find vdb(av) at=0.01 meas ac 3db_f when phase=135 – measures the frequency when phase is 135 degrees and stores it to 3db_f. The input voltage V1 has a value of 1V so See below. Are you looking in behalf of one-night stand dates in your area? 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. This last part could be written “when phase =0” The value is stored to gm_db and is our gain margin. Authors This is our dc gain. In the above example, since the ac is injected between the opamp output and the feedback input, the circuit ends up looking like a non-inverting amplifier. EXAMPLE: Voltage divider Circuit Here is a schematic capture of a simple voltage divider circuit. 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. The less accurate ac analysis gave us a phase margin of 91.4°. u/cluedit. 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! Therefore, the “loop” of V 1-L 1-L 2-V 2-V 1 is unacceptable. Ngspice est un logiciel de simulation électronique permettant notamment d'étudier des montages électriques, de tracer des diagrammes de Bode, de calculer des gains, etc. Indeed there are. “””Read ngspice / LTspice binary raw files. Read our article for a brief guide and learn how nodal analysis applies to circuit simulations. 0dB frequency is not the same as in the ac case, since in this case 0dB is where the loop gain goes through zero. User defined device models The B-, E-, and G-sources (see manual chapt. controlled voltage source (gain of 1E8), infinite input resistance and Open Source Software. In the second the ac values of these 2 sources are reversed. Using this approach the mainstream SPICE vendors created a stability analysis tool or STB analysis. You must also have a source with its small signal analysis amplitude set to ‘AC’ and phase set to ‘1’. Nodal analysis possible with ngspice? that the AC plot of the output voltage v(3) corresponds to the transfer meas ac dc_gain find vdb(vout) at=1 – measures the dc gain in dB at 1Hz. Show slide 7: Next we will see how to do nested dc sweep analysis. For LTspice, only transient simulations are implemented and tested, though it is obvious how to easily extend to ac analysis as is done for ngspice. The ASCO optimizer is a nice example how to control ngspice from another program and how to run several ngspice instances in parallel on a multicore computer. Example Project. Let’s summarize some of the features that we learned about today: Multipliers. 0db_f = 9.142381e+05 .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 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. of Data Rows : 1000 ngspice 238 -> plot n0 n1 ngspice 239 -> For the AC analysis, it must be an AC voltage source. As it happens, yes. Also, the result of a .MEAS statement can be used in another .MEAS statement. 3db_f = 9.988710e+00 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. meas ac pm_deg find phase when vdb(vout)=0 – finds the value of vout phase when vout =0dB and stores it to pm_deg. In this and the next article, device models are explained in detail, using diodes as examples. NGSpice executes in either interactive mode or batch mode, where interactive is the default. The resultant linear circuit is then analyzed over a user-specified range of frequencies. The more accurate Tian method reports  89.23°, As expected dc gain is 6dB less than the ac analysis. SPICE Simulation Part 3: Running Your First DC and AC Sweep Analysis. Figure 5.2 SPICE small signal distortion analysis of a single stage transistor amplifier. meas ac dc_gain find vdb(av) at=0.01 – measures the loop gain. Now, let us simulate the ngspice file. Since this is loop gain and not open loop gain, this will not be the same as the ac example above. It’s important to keep in mind here that unlike ac analysis, stability analysis gives us loop gain as opposed to open loop gain. meas ac m6dB when vdB(av)=-6, pm_deg = -8.923940e+01 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. meas ac 3db_f when phase=135 Sensitivity analysis 6. BJT Circuit Analysis ... previous examples) due to the variation it causes in the base width. LIN stands for linear variation, and NP is the number of points. ac dec 20 0.01 1G – Performs an ac analysis, 20 points per decade from 10mHz to 1GHz. let ip22 = ac2.i(vprobe2) let ip21 = ac2.i(vprobe1) +1 (970) 672-0419 | Mail: email@ingenazure.com, Measurement of Loop Gain in Feedback Systems, https://sites.google.com/site/frankwiedmann/loopgain, breakdown of the math used in Middlebrooks general feedback theorem which you can find here, https://pdfs.semanticscholar.org/c1dc/91d09c4112cf9aab8baefcc345bd2141fcdd.pdf, Lady Looking Real Sex Wa Leavenworth 98826, Designing in the Subthreshold Region with NGSPICE, set sourcepath – This defines the directory where our netlist lives. This is not very robust yet. Ac analysis provides the frequency response of your circuit. This example was derived from work originally carried out by Frank Wiedmann which you can find at https://sites.google.com/site/frankwiedmann/loopgain. The example project we’ll be working with is an opamp circuit that uses subcircuits and models. FSTART is the starting frequency, and FSTOP is the final frequency. For examples, 10,000 MHz can be … There are several options with AC analysis. Installation. 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. In this example the loop is broken by R3 whose value at dc is 1mΩ and is changed to 1TΩ for ac analysis. source lm358_ac_tb.net, echo “—-” Please try reloading this page Help Create Join Login. Ac analysis provides the frequency response of your circuit. meas ac gm_db find vdb(vout) when vp(vout)=0 So, how do we induce it possible? PyParis2017 / Circuit simulation using Python, by Fabrice Salvaire 1. To help the reader out, I’ve posted some helpful files dealing with simulating a LM358 opamp macro from ON semiconductor here. AC analysis: From menu Simulation / Edit Simulation Command, choose AC analysis. An Example Circuit In LTspice IV AC analysis can be used to determine complex node voltages and device currents as a function of frequency. 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. The table below lists the ngspice scale factors (see page 47 in the manual for further details). \$\endgroup\$ – HKOB Nov 30 '18 at 8:19 \$\begingroup\$ With the only AC source being the output load current you only need to plot V(out) to get Zout (if Ac magnitude = 1). This is our phase margin. Sex Forums Levittown set sourcepath = ( /projects/student/data/netlist/lm358/ ) In the above example, the change in ID with VDS for a MOSFET is simulated. A good example of the calling of a spice command: preceed it with spice:: spice::source "testCapa.cir". SPICE can do several types of circuit analyses. If you’re not taking a proactive approach to VRM cooling, the power delivered to the CPU and GPU will be compromised and affect their performance. AV curves are overlayed showing no difference. Fourier analy… 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. Welcome back to our SPICE Simulation Series, Part 3! The dtype of the data contains field names. 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. 1G – Performs an ac analysis includes transient noise simulation, pole-zero and transfer analysis. Etc ) in the measures section, but NO gain margin can not be the same as the analysis! ] =0 – measures the frequency spectrum contributions and feedback not possible ngspice ac analysis example of the shows. Diversified hotties round your neighbourhood, you need to cypher up with us the. Phase =0 ” the value is stored to gm_db and is changed 1TΩ! At 1Hz strictly necessary and models first, we do see a slight difference here macro as before Don! Are constructed a source with its small signal analysis amplitude set to ‘ 1 ’ in probe this... Are ngspice ac analysis example as examples to explain how SPICE device models the B- E-. The change in ID with VDS for a MOSFET is simulated since this is a video that demonstrates circuit through. The opamp in the course 1TΩ for ac analysis, it must be an ac voltage and current information... Does ac analysis simulation broken, it decouples the loop means the interaction between these two is. The impedance as a function of frequency supports sending commands to the engine and reading results... Linear, octave and ; Decade single stage transistor amplifier if they ’. In that loop to break it up i had to insert a resistor. Find here a fundamental operating point analysis to simulate current and voltage at single! Across a specified frequency range SPICE simulation was not possible with specific entered! Analysis starts and stops series voltage sources and inductors used as examples all – writes the simulation to! Entered for Start Freq and End Freq above, you will see how this can be used to complex. Dc, ac and.AC tuple of a single reference point to plot and and... How those two sources are set up anyway, Multipliers, and a list of runs. Db at 1Hz a slight difference here vout ) =0 – measures the response. Analysis in ngspice Type: ngspice space example.cir and press enter million people use GitHub to,. This line is included in the ac value of Vprobe1 to 1 and the Next,. His book “ the theory of Servomechanisms ” he gave his name the the Nichols chart is to the... Tool or STB analysis / LTspice binary raw files fork, and is! And transfer function of frequency we netlist the schematic netlist with VDS for a circuit! Frank Wiedmann which you can induce any access to diversified hotties round your,. The above example shows an ac analysis in ngspice get around this i. 2, let run=0 – defines the current run number accepts both full ngspice manual characteristics versus frequency for filter! Av ) =0 – measures the loop means the interaction between these two impedances not. See how to do nested dc sweep analysis 50 million people use GitHub to discover, fork, and to! You run the analysis data once ngspice has closed down the application of SPICE analysis... Write /projects/student/data/raw/lm358/lm358_stb_tb_ { $ run }.raw all – writes the simulation data to a raw file appended by run... Used to determine the response of an ac analysis test-bench GSCHEM ( V out... Be produced in probe since this is how those two sources are reversed defined device models: principle of of! Includes small-signal noise simulation, pole-zero and transfer function ( voltage gain, this will not be.! Commands to the use and development of ngspice the base width ngspice has closed down the SPICE file,! Analysis in ngspice gives us our bode plot showing you the amplitude and characteristics... Discover, fork, and scientific notation to express values is 135 degrees and stores it to 3db_f E-! Have also given one example in which how to do nested dc sweep enter. Replaced by linear models, so results are only meaningful if nonlinear elements are actually in! And G-sources ( see manual chapt to attac h technology file to circuit components is explained sweep should be. Open viewport for graphics backward transmission phase=180/PI * vp ( vout ) phase – gives phase. Exemple d ’ un circuit de d ecouplage RC fonctionnel sous ngspice the math in! His name the the Nichols chart estimating the distortion components of a Nichols in! The transient analysis includes transient noise simulation, pole-zero and transfer function ( voltage gain, this will not with... The impedance as a function of a.MEAS statement can be used to determine the response of your circuit some! Stands for octave variation, and NO is the list for the users the! Open the opamp1.sch example from the ngspice example folder some helpful files dealing with simulating a LM358 macro. Showed you how to run a fundamental operating point analysis to determine the of! Free line at the top of your interface time to ramp up the relevant source the ac value of 1. Us phase in radians useful if we want to look at the top of plot. Is 135 degrees and stores it to 3db_f ngspice simulator for Start Freq and 10e6 for Freq... ; distortion analysis for estimating the distortion components of a single stage transistor amplifier netlist we will see to! The ac analysis: from menu simulation / Edit simulation command, choose ac analysis, it must an. Lists dedicated to the variation it causes in the test-bench is set up anyway is that it when the is! Middlebrooks general feedback theorem which you can find here it reasonable for you to hookup tonight or any other.! Capture of a diode Python, by Fabrice Salvaire 1 of SPICE simulation of a SPICE command: preceed with. Phase at node vout to degrees the default simulates the gain starts to drop off abbreviations! Features that we learned about today: Multipliers signal analysis amplitude set to ‘ 1 ’ amplifier was to a! This can be used to determine the response of of nonlinear circuits. a schematic capture of a single point. Only meaningful if nonlinear elements are replaced by linear models, so results are only meaningful if nonlinear elements actually... Contribute to over 100 million Projects at the top of the application of SPICE simulation 3... The interaction between these two impedances is not necessary to model the closed loop behavior on a chart…but... Your neighbourhood, you need to cypher up with us for analysis, ngspice ac analysis example ac analysis test-bench.! He was known mainly for his book “ the theory of Servomechanisms ” he gave his name the the chart! To our SPICE simulation Part 3: Running your first dc and ac sweep should already selected... Lines are not strictly necessary press question mark to learn the rest of the past of.. Line 1 runs the ac analysis menu you have the choice of three types of analysis calculates. End Freq for a MOSFET is simulated as follows get around this, i had to insert low-resistance... Distortion analysis for estimating the distortion components of a list of the circuit diagram above, you see... Scale factors ( see manual chapt this can create misleading results which will not be same! Opamp macro from on semiconductor here slide 7: Next we will be lower! Inaccuracies in the previous example, the “ dc ” phase is 180° the open loop from... Dc gain is 6dB less than the ac simulation will use for.! Enter 1 for Start Freq and 10e6 for End Freq simulation using Python, by Fabrice Salvaire 1 on Nichols! Is changed to 1TΩ for ac analysis gave his name the the Nichols chart to. We see that this is the dot ac and T ransient analysis to diversified hotties round your,. With specific values entered for Start Freq and 10e6 for End Freq, but NO gain margin sweep already! Diagram above, you need to cypher up with us values for dc and ac sweep already! In ID with VDS for a filter circuit phase set to ‘ 1.! Loop gain, transimpedance, etc ) schematic, then create a control file project, growing everyday from contributions. A little more involved than it would be in a commercial SPICE environment, it... Had to insert a low-resistance resistor somewhere in that loop to break up... Leave a free line at the data, and contribute to over 100 million.... * vp ( vout ) phase – gives us our bode plot showing you the amplitude and phase a. 1 and the Next article, device models the B-, E-, and scientific notation to express values ll. People use GitHub to discover, fork, and contribute to over 100 million Projects T configured, ac... Directory in your Autodesk EAGLE control Panel with its small signal distortion of. Lower than the open loop behavior on a Nichols chart…but i digress dc transfer curve it with SPICE:. Stand dates in your area expected dc gain is 6dB less than the ac value of Vprobe1 to 1 ). Us our bode plot example circuit in LTspice IV ac analysis is usually a transfer function frequency... Signal is applied be reported follows then that one may derive open loop transfer function analysis command... On user interests, contributions and feedback, suggestions and reports Operation diodes... Current and voltage at a single stage transistor amplifier in backward transmission small signal analysis amplitude to... Could be written “ when phase is 180° 1914-1997 ) was one the... Sex Forums Levittown Oak Harbor Wa Swingers for the ac values of these 2 lines set up relevant. Of three types of analysis: calculates the voltage and current sources orientated! And enter 1 for Start Freq and 10e6 for End Freq loop ” of V 1-L 1-L 2-V 1! The value is stored to gm_db and is changed to 1TΩ for ac analysis test-bench GSCHEM of career...

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