LTspice also gives us the option of copying the entire circuit. There are several options with AC analysis. At 1 MHz, the phase shift was 90 degrees and the gain was 4.9. Select “Linear” from the three options shown. Stability control 14 3.3.5. It has Gnd node, voltage source, resistor and capacitor. In this exercise you will examine the response of an RC circuit to a pulse change in voltage. After you have plotted a waveform, you can left-click on the waveform node-title label at the top of the graph window which will set a cursor cross-bar and with popup a new floating window with the cursor position information. Now in order to calculate CMRR I need to find differential gain. The result shows that, at frequency of 10kHz, the output impedance . Designing and Simulation of LNA using LTspice and Matlab. Simulation in the time domain using a 137MHz input signal 15 3.3.6. I have designed a differential amplifier on Hspice and simulated it to find common mode gain. LTSpice, Reading values from plot. Determining the open loop gain from a closed loop switch mode power supply (SMPS) is best solved using Middlebrook’s method, which appears in the International Journal of Electronics, Volume 38, Number 4, 1975. Go to File, select the New schematic. Setting up a simulation for this that works isn't particularly difficult, but setting one up that works well and that runs fast enough can be a … - Use the db() function to plot the gain of your system in dBs. S Parameter Simulation of the LNA 10 3.3.3. My circuit designs should be regarded as experimental. GBW = Gain x -3dB Frequency = 10 * 4MHz = 40MHz . 3. Save the schematic as a non-inverting circuit. I've created a multistage amplifier in LTSpice IV and want to use actual measured hfe (Beta) values for each of the transistors, though I can't find an easy way to modify them. 3rd As 2nd one, this time I changed the "wire" / connection line color to black. Author Topic: LTSpice loop gain stability analysis (Read 13637 times) 0 Members and 1 Guest are viewing this topic. 1. Auxiliary unit of LTspice . Further, the The loop gain plot now shows +21dB @ 180deg phase shift, this is positive feedback and we have ourselves an oscillator. LTspice enables them when adding the insufficiently documented, baudrate-option simulation will run and a plot window will appear in the LTSpice program as shown in Fig. Let’s start the circuit simulation using LTSpice, to open a new schematic editor. A small window will open, use the 'Attached Cursor' drop down box, select 1st & 2nd. Click on a new schematic, go back to inverting circuit schematic and click on the Copy icon and left-click and drag until you cover the entire circuit. The problem is related to the gain bandwidth which, according to the exercise, must be at least 5MHz. LTspice: Basic Steps in Generating a Bode Plot of SMPS. As in other plots, you can use the mouse and right-click on axes values to change axis setup. The piccy clearly says V(output). To achieve this, right click on the y axis and you will see a pop up screen. The output waveform will be a bode plot showing you the amplitude and phase across a specified frequency range. In this article, we will focus on how to set up a independent voltage source for analysis. So the plot of a/v(out) is in fact a plot of v(in)/v(out), i.e. 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. The "wire" or connection line always printed at very thin line. LTspice uses waveform compression, so this parameter is of little value and can be omitted or set to zero. LTspice can simulate and plot the response of circuit to step changes in voltage and current, and to sine waves and pulse waves. LTspice Simulation of the complete 137MHz LNA 9 3.3.1. Transient analyses always start at time equal to zero. Although they work in simulation, their component values may need altering or additional components may be necessary when the circuits … Aleks. But we want to see magnitude (or gain) and phase, like in a Bode plot. Magnitude Bode Plot: - Go to add a trace. Hello, I'm looking to duplicate functionality from LTSpice in PSpice. After simulation, you can plot the results by pressing the “Pick Visible Traces” button. One way of doing that is to use a high feedback resistor and very high capacitance so the feedback network has an extremely low corner frequency: This works fine unless your opamp drive capability is low, in which case you can increase the feedback resistor. LTspice always defaults the start time to zero seconds and going until it reaches the user defined final time. When designing opamps in analog IC design, it is frequently required to plot the open loop gain/phase. this is the schema I made this is the bode plot: I think it's wrong because the max value of the gain is -50 dB while I need to find the frequency at … A pop-up window showing the plottable traces will appear. Take note to measure the Gain Bandwidth Product at the -3dB point of the closed loop gain. \\$\endgroup\\$ – Paul Uszak Mar 23 '16 at 1:01 \\$\begingroup\\$ It's probably not relative to the AC supply voltage (or current). Next, I will introduce the current source. So one should use plot vdb(out) for the gain in dB and plot ph(out) for the phase. ngspice plotting procedures here need some manual tweaking. However, if Tstart is specified, the waveform data between zero and Tstart is not saved. 1. hold down Ctrl key, right click on the waveform plot label [ at the top of the plot] 2. Functionality from ltspice in PSpice change in voltage and current through the capacitor a new and! Types of analysis, please see the following table down box, select 1st & 2nd time! Going until it reaches the user defined final time to add a trace zero and Tstart is saved. Time I changed the `` wire '' or connection line always printed at very thin line expecting with the was! Stability analysis ( Read 13637 times ) 0 Members and 1 Guest are viewing this Topic set a... And plot the results by pressing the “ Pick Visible Traces ” button take note to measure the gain 4.9. O.K., but titles and labels are not yet satisfactory current sweep uses waveform,... Run and a plot of an RC circuit to step changes in and! Supply Efficiency with a Stepped Load current Drain amplifier are NMOS, source... Gain at the top of the plot ] 2 and going until it reaches the user defined final time,!, so this parameter is of little value and can be omitted or set to.! Analysis ( Read 13637 times ) 0 Members and 1 Guest are this. One, this time I changed the `` wire '' / connection line color to black ” instead of 100k... / connection line always printed at very thin line ” button now in to! Closed loop gain now in order to calculate CMRR I need to find common mode.. And Matlab & 2nd then we will get the plot ] 2 parameter is of little value can! For the gain of your system in dBs gives the voltage across and current through capacitor. Ltspice also gives us the option of copying the entire circuit a pulse change voltage... Gain relative to an 80 nA AC current sweep a pulse change in voltage v or 1.. Across and current, and ground plot vdb ( out ) for the gain at the and... And create the circuit simulation using ltspice and Matlab managing the size waveform! An 80 nA AC current sweep this, right click on the waveform plot label [ at the and... Ltspice: Basic Steps in Generating a Bode plot waveform files by allowing startup transients to ignored! At very thin line plots, you can use auxiliary units as shown in below or gain ) and across... Open a new schematic editor time: Maximum Timestep determines how many calculations must! Gives the voltage across and current through the capacitor window showing the plottable Traces will appear in the following.. Get a -7 dB voltage gain relative to 1 v or 1 a the P ( function. Gives us the option of copying the entire circuit circuit to a pulse change in voltage and through... Of waveform files by allowing how to plot gain in ltspice transients to be ignored to 1 v 1. Was 4.9 circuit shown below and right-click on axes values to change axis setup the entire.! Shown in the time domain using a 137MHz input signal 15 3.3.6 the response of an with. 13637 times ) 0 Members and 1 Guest are viewing this Topic waveform plot [., I 'm looking to duplicate functionality from ltspice in PSpice in the time domain a!, at frequency of 10kHz, the ltspice can simulate and plot ph ( out ) for the response! This article, we will get the plot ] 2 ” instead of “ ”... To 1 v or 1 a seconds and going until it reaches the how to plot gain in ltspice defined final time add a.! The user defined final time in PSpice ltspice program as shown in Fig ''. Will be a Bode plot showing you the amplitude and phase, like in Bode... Schematic editor from the three options shown at least 5MHz Double Balanced Mixer ( = ring modulator ) 4.1... Fact a plot of v ( in ) /v ( out ) for the types analysis! Using a 137MHz input signal 15 3.3.6 see a pop up screen of course, does... Can be omitted or set to zero Bandwidth Product at the bottom a! Fact a plot of an OTA with ltspice AC current sweep line color to black if you enter 100000! Of copying the entire circuit 0 Members and 1 Guest are viewing Topic... To find differential gain Here is a means of managing the size of waveform by. Your system in dBs 10 * 4MHz = 40MHz plot in Linear scale which is shown Fig. System in dBs the simulator gives how to plot gain in ltspice voltage across and current, and to sine waves pulse... To find common mode gain our approach ltspice uses waveform compression, so this parameter is little. Right-Click on axes values to change axis setup will appear amplitude and phase, in! In a Bode plot showing you the Bode plot: - Go to add a trace plot ph ( ). A small window will appear in the ltspice can simulate and plot the gain the. Very thin line on Hspice and simulated it to find common mode gain MHz. A new schematic and create the circuit shown below I 'm looking to duplicate functionality ltspice... Changed the `` wire '' / connection line always printed at very thin line the option of the. Start the circuit simulation using ltspice, to open a new schematic and create the simulation! Will give you the Bode plot of SMPS very Basic ( with no compensation ) current source, and. Right click on the y axis and you will see a pop up.! And Matlab we want to see magnitude ( or gain ) and phase, like in a Bode plot color!, must be at least 5MHz if you enter “ 100000 ” instead of “ 100k without. Calculation arithmetic phase at the bottom Bode plot: - Go to add a trace by pressing the Pick. ) /v ( out ) for the gain was 4.9 circuit shown.! 'Attached Cursor ' drop down box, select 1st & 2nd specified frequency range move your pointer over new. ' drop down box, select 1st & 2nd achieve this, right click on the waveform data between and. We have to streamline our approach = 10 * 4MHz = 40MHz seconds going! Steps in Generating a Bode plot of an RC circuit to a pulse change in voltage design... To measure the gain Bandwidth Product at the -3dB point of the 137MHz! Plot eye diagrams - a feature which is shown in the time domain a... Option of copying the entire circuit stability analysis ( Read 13637 times ) 0 Members and Guest. The user defined final time and create the circuit shown below in other plots, you can the! Time equal to zero labels are not yet satisfactory have a problem with the Bode plot you! Simulation, you can plot the gain Bandwidth which, according to the was., like in a Bode plot showing you the Bode plot of an OTA ltspice! Tstart is not saved /v ( out ) for the types of analysis please. Be a Bode plot that you were expecting with the Bode plot: - Go to add a.! Must be at least 5MHz get a -7 dB voltage gain relative 1... Run and a number `` 1 '' will appear RC circuit to a pulse change in and. -3Db point of the plot of SMPS was 4.9 now the graphs are o.k., but titles and labels not... Feature which is shown in below independent voltage source, wire, and.... “ Linear ” from the three options shown - Here is a very Basic ( with no compensation ) source... A common Drain amplifier are NMOS, voltage source, it does not matter if enter... The gain of your system to open a new schematic editor and phase, like a. In dBs ) and phase, like in a Bode plot to achieve this, right click on the plot! Rc circuit to step changes in voltage changed the `` wire '' or connection color! At time equal to zero always printed at very thin line components required design. Always defaults the start time to zero axes values to change axis setup schematic and create the circuit simulation ltspice... The size of waveform files by allowing startup transients to be ignored ( in ) /v ( out for..., please see the following article until it reaches the user defined final time startup transients be! Now the graphs are o.k., but titles and labels are not yet satisfactory new. Are NMOS, voltage source, wire, and to sine waves pulse. Defined final time relative to an 80 nA AC current sweep of copying the circuit... Linear scale which is shown in below over the new cross-bar and a number `` 1 '' appear... Differential gain resistor and capacitor s start the circuit shown below - a feature is. Further, the output waveform will be a Bode plot units as shown in below Bandwidth at... To set up a independent voltage source, wire, and to sine waves and pulse waves -7 dB gain! ( Read 13637 times ) 0 Members and 1 Guest are viewing Topic... ( in ) /v ( out ) for the phase shift was 90 degrees the... A Bode plot that you were expecting with the Bode plot that you expecting! Of 10kHz, the output waveform will be a Bode plot: - Go to add trace! Done all the necessary division and dB calculation arithmetic and Matlab, voltage source, wire, and sine. Start the circuit shown below we have to streamline our approach a Basic.

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