Parametric Sweep

Manta Cario/Wwtt Cate Parametric Sweep T omparatiao (Sweep) Save Biat Point Load Biat Point... 

Secondary Sweep Monts Carto/Worst Case Parametric Sweep Temperature (Sweep) Save Bias Point Load Bias Point... 

In general, we can run the temperature sweep as either a Parametric Sweep or a Secondary Sweep. However, to generate I-V characteristic curves for different temperatures, we must use the Secondary Sweep. Click on the square D next to the Secondary Sweep selection ... 

With the Secondary Sweep, we cannot easily identify which trace occurs with what temperature. To associate a trace with a specific temperature, we would need to run a single I-V characteristic at the specified temperature. If we ran a DC Sweep (sweep variable Vin) together with a Parametric Sweep (sweep variable temperature) we could then identify which trace was at what temperature. However, we cannot generate the I-V characteristic using the Parametric Sweep together with the DC Sweep. 

In circuit design, we are sometimes concerned with how a circuit parameter affects performance. There are two ways to vary parameters in PSpice. The first is the DC Sweep, where we vary a parameter rather than a DC voltage. This method generates a single curve. The second is a Parametric Sweep that is run in conjunction with another analysis such as an AC Sweep, DC Sweep, or a Transient Analysis. The second method generates a family of curves. In this section we will demonstrate only the DC Parametric Sweep. Throughout this manual there will be examples using the Parametric Sweep in conjunction with the other analyses. 

Secondary Sweep Mont Certo/Worot Case Parametric Sweep TTamperaiure (Sweep) Save Bia Point Load Bia Point... 

Using a Secondary Sweep, we cannot have Probe identify which trace occurs at which value of the breakdown voltage. We could have generated this same family of curves using a DC Sweep together with a Parametric Sweep. An example is shown for an NMOS inverter in Section 4.D.5. Follow the procedure of Section 4.D.5 and set the DC Sweep variable to Vs and the Parametric Sweep to the Model parameter BV. You can then follow the procedure at the end of Section 4.D.5 to identify which trace is associated with which value of the breakdown voltage (BV). 

A question we would like to ask is, how does the transfer curve of the circuit from the previous section change as we change the driver MOSFET width-to-length ratio We would like a family of curves that show the effect of changing the driver width. Families of transfer curves can be generated using the Parametric Sweep in conjunction with the DC Sweep or by using the Secondary Sweep. The Secondary Sweep was demonstrated in Section 4.D.2, so we will demonstrate the Parametric Sweep here. 

A Parametric Sweep allows us to sweep a parameter. We would like to sweep the width of the driver MOSFET in the circuit of the previous section. We are assuming that you have followed that procedure and have set up the MOSFET models and DC Sweep. We must first set up a parameter for the width of the driver. We will start with the completed circuit from the previous section. It is repeated here for convenience. 

We must now set up the Parametric Sweep. If you are continuing from the previous example, you will already have created a simulation profile for the DC Sweep. To open the profile, select PSpice and then Edit Simulation Profile from the menus. If you started this example as a new circuit, select PSpice and then New Simulation Profile, specify a name for the new profile, and then click the Create button. Set up a DC Sweep as shown below. Using either procedure, you should have the screen below ... 

The parameters for the Primary Sweep are set up and the sweep is enabled. We must now set up the Parametric Sweep. Click the LEFT mouse button on the D next to the text Parametric Sweep to toggle to the Parametric Sweep settings ... 

The PSpice window indicates the current value of the parameter. Notice that for each value of the parameter, the input voltage is swept from 0 to 5 volts. Logically, the DC Sweep loop is executed inside the Parametric Sweep loop. When the simulation is complete, you will be asked which values of W VBl you would like to view. By default, all runs are selected ... 

Set up the Primary Sweep to sweep l/Z/I from 0 V to 5 V in 0.001 V steps as shown in the left dialog box below. Set up the Parametric Sweep to use the value list as shown in the right dialog box ... 

HSacondaiy Sweep DMonta Cailo/Woret Cate Parametric Sweep Tamperatura (Sweep)... 

The Secondary DC Sweep and the Parametric Sweep can be used to see how values of devices affect the performance of a circuit. 

Monte CarloAVorsI Casa Parametric Sweep Temperature (Swaep) Sava Bias Point load Bias Point... 

The value specified here is the default value for the parameter. If we do not modify the parameter in a DC Sweep or in a Parametric Sweep, the value of the parameter will be the one specified here. Click the OK button to accept the settings and add a new column to the spreadsheet ... 

We would like to see the frequency response of the op-amp circuit for different values of the gain, so we must set up an AC Sweep to run in conjunction with a Parametric Sweep. First we will set up the AC Sweep. Select PSpice and then New Simulation Profile from the Capture menus and then enter a name for the profile and click the Create button. Select the MT Sweep/Nolse Analysts type and fill in the parameters as shown in the AC Sweep dialog box below ... 

We would now like to set up values for the parameter RF Val. Parameters can be changed using the Parametric setup dialog box. Click the box next to the text Parametric Sweep. 

The square fills with a checkmark 0 indicating that the option is selected, and the dialog box for the parametric sweep is displayed. Fill in the dialog box as shown ... 

The parameter we have defined (RF val) is a Global parameter. The sweep settings are similar to the DC and AC Sweeps discussed previously. We would like specific values for the parameter, so we will use the value list. Logically, the parametric sweep is executed outside the AC Sweep. First, RF Val will be set to Ilf and then the AC Sweep will be performed. Next, RF val will be set to lOh and then the AC Sweep will be performed. Then, RF val will be set to lOOH, and so on. Click the OK button to accept the settings to return to the schematic. 

The Performance Analysis capabilities of Probe are used to view properties of waveforms that are not easily described. Examples are amplifier bandwidth, rise time, and overshoot. To calculate the bandwidth of a circuit, you must find the maximum gain, and then find the frequency where the gain is down by 3 dB. To calculate rise time, you must find the 10% and 90% points, and then find the time difference between the points. The Performance Analysis gives us the capability to plot these properties versus a parameter or device tolerances. Hie Performance Analysis is used in conjunction with the Parametric Sweep to see how the properties vary versus a parameter. The Performance Analysis is used in conjunction with the Monte Carlo analysis to see how the properties vary with device tolerances. In this section we will plot the bandwidth of an amplifier versus the value of the feedback resistor. See Sections 9.B.3 and 9.E to see how to use the Performance Analysis in conjunction with the Monte Carlo analysis. 

EXERCISE 5-9 Plot the gain bandwidth of the amplifier in the previous example versus the feedback resistor RF. SOLUTIOIl Rerun the simulation with more detail in the Parametric Sweep ... 

The Performance Analysis is the use of a goal function in conjunction with a Parametric Sweep. The result of the goal function is plotted versus the swept parameter. 

Now that we know what the input and output waveforms look like, we will see how changing the collector resistor RC affects the waveform. Return to the schematic. The Parametric Sweep can be used to change the value of any circuit parameter. First we must define the parameter we want to change. Get a part called PARAM and place it in your circuit ... 

We will now set up a Parametric Sweep to change the value of the parameter. Suppose we want to see the performance of the circuit for values of RC from 1 k 2 to 10 k 2. We need to set up a Parametric Sweep. Select PSpice and then Edit Simulation Profile from the Capture menus ... 

Note that there are no curly brackets around the parameter. Click the OK button to accept the value and return to the schematic. Logically, the Transient Analysis executes inside the Parametric Sweep. That is, for each value of the parameter, the Transient Analysis is run. Thus, for this setup, ten Transient Analyses will be run. Since we chose a small Maximum time step in the Transient Analysis setup, this simulation will take a long time to run. To speed up the simulation, you may want to increase the value of the Maximum time step. 

Modify the Parametric Sweep to sweep parameter RB val from 5 kQ to 30 kQ in 5 kQ steps. Note that the Transient Analysis will run six times. 

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