The Easily Overlooked Feature section describes the pop up menus available when the mouse is right clicked in the Page or P fields within the Analysis Limits dialog box. These menus provide a quick way to sort, enable, hide, or disable groups of waveforms. The first article describes how to optimize the XTI, TRS1, and TRS2 model parameters for the diode to produce accurate forward voltage versus forward current curves with respect to temperature. The second article describes time domain reflectometry TDR which is a method by which a short duration pulse with a very fast rise time is injected into an electrical line.
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The Easily Overlooked Feature section describes the pop up menus available when the mouse is right clicked in the Page or P fields within the Analysis Limits dialog box. These menus provide a quick way to sort, enable, hide, or disable groups of waveforms. The first article describes how to optimize the XTI, TRS1, and TRS2 model parameters for the diode to produce accurate forward voltage versus forward current curves with respect to temperature.
The second article describes time domain reflectometry TDR which is a method by which a short duration pulse with a very fast rise time is injected into an electrical line.
The reflected waveform from this pulse can be used to calculate the characteristics of the line such as the impedances and propagation delays along the signal path. The third article describes how to use performance functions to measure the power factor in a linear circuit. Contents News In Preview Sandler, McGraw Hill, Micro-Cap Questions and Answers Question: I would like to simulate coupling between multiple inductances in my circuit. I have placed the inductor components in the correct locations.
How do I couple these inductors together? Answer: The K component available in Micro-Cap will couple inductors using either the linear mutual inductance or the nonlinear Jiles-Atherton core magnetics model.
The procedure for each of the possible couplings is as follows: Linear Mutual Inductance 1 Place an inductor component in the schematic for each inductance that is to be coupled.
The K component has no external connections so it can be placed anywhere in the circuit. Upon hitting OK in the Attribute dialog box, the specified inductors will then be coupled. Nonlinear Jiles-Atherton core magnetics model 1 Place an inductor component in the schematic for each winding that is to be coupled. The number of turns must be a constant, whole number. In this case, the list can contain just one inductor. A single inductor will create a single magnetic core device not coupled to another inductor.
The presence of a model name signifies that this coupling will use the Jiles-Atherton model. Upon hitting OK in the Attribute dialog box, the specified inductors will now use the nonlinear Jiles-Atherton magnetics model. Easily Overlooked Features This section is designed to highlight one or two features per issue that may be overlooked among all the capabilities of Micro-Cap.
The Page field specifies which analysis page the waveform will be displayed in, and the P field specifies which plot group the waveform will be displayed in. Right clicking in any of the Page or P fields invokes a pop up menu that provides the following operations: Sort - For the Page field, this sorts all of the expressions in the analysis limits so that the page names are in alphabetical order.
For the P field, this sorts all of the expression in the analysis limits by the value in the P column. Enable - For the Page field, all expressions that share the same page name will have their status set to enabled.
For the P field, all expressions that share the same P value and the same page name will have their status set to enabled. Hide - For the Page field, all expressions that share the same page name will have their status set to hidden. For the P field, all expressions that share the same P value and the same page name will have their status set to hidden.
A hidden waveform is one whose data is stored in memory during the simulation, but the waveform is not initially displayed in the plot.
The waveform can be added to a plot after the simulation is finished within the Plot page of the Properties dialog box. Disable - For the Page field, all expressions that share the same page name will have their status set to disabled. For the P field, all expressions that share the same P value and the same page name will have their status set to disabled.
For the enabled and hidden waveforms, a valid value in the P column must also be specified for these waveforms to be calculated. If the P column is blank, the waveform is disabled no matter what the status is set to. Most device models are optimized at either 25 or 27 degrees Celsius which is considered room temperature.
The circuit optimizer that is available in transient, AC, or DC analysis for Micro-Cap can be used to derive the temperature parameter values for more accurate simulation results. XTI is the saturation current temperature coefficient and is used to change the diode saturation current sensitivity. These two parameters operate in the same manner as the temperature coefficients for the resistor component.
The circuit below is used to plot the forward current versus forward voltage curve. The diode model is the 1N fast recovery power rectifier whose data was derived from the Motorola "Rectifiers and Zener Diodes" data book. The only other component in the schematic is a battery with the part name Vf that will be used to sweep the forward voltage across the diode.
In the DC analysis limits, the Vf battery is swept linearly from. The Temperature field is set to run two branches of the simulation. One branch will be run at C. The second branch is run at 27C just to show the nominal curve of the 1N diode. The resulting DC simulation is shown below. The green curve is the branch when the temperature is set to 27C and provides an excellent match to the equivalent curve shown in the Motorola data book.
The red curve is the branch when the temperature is set to C. This curve is a good deal off from the one specified in the data book which shows that the default temperature parameters in the model are not a good match for this device. To enter the optimizer, select the Optimize command in the DC menu.
The Find section specifies the parameters that are to be optimized. All three parameters are setup to be optimized within the D1 component in the schematic. The parameter to be optimized can be selected by clicking on the Get button. Since the object in this optimization is to match the forward current from the Motorola data book at C, the optimizing criteria in the That section for each function is set to Equates.
This is the criteria that needs to be used for any curve fitting operation. For example, with the first expression in the list, when the forward voltage is. Since six performance functions have been specified, the optimizer will find the values of XTI, TRS1, and TRS2 that produce the curve that creates the smallest total RMS error between the target and actual values at each point. Each of the Equates conditions are weighted equally in terms of importance when optimizing.
Clicking on the Optimize button initiates the optimization. The Powell optimization method finds the closest match to the specified data points. The optimizer has calculated a value for XTI of The values for these parameters produce a good match to the data book values having just a 3. Applying the updated parameters from the optimizer does not actually overwrite the 1N model in the Micro-Cap library file, but it localizes the model in the Models page of the schematic so that the changes only affect this specific circuit.
The model statement could then be copied into the Micro-Cap library or copied into any other circuit file that would use the model.
The updated model for the 1N appears as follows:. Running the same schematic with the updated model statement produces the forward current versus forward voltage curves shown below. The green curve for the 27C branch has not changed at all. However, the red curve for the C now closely matches its equivalent curve from the Motorola data book.
This measurement can give a good indication of any discontinuites within the line that would occur with an open, short, or any other impedance mismatch. Both of the examples used in this article were derived from the Maxim application note shown in Reference 1. The schematic shown below is used to demonstrate the basics of a TDR measurement. There are three separate circuits in the schematic.
The only difference between the three is the value of the load resistance. The top circuit models a short at the line output. The middle circuit models an open at the line output. The bottom circuit models the case where the load impedance matches with the line impedance.
A voltage source at the input to each of the circuits injects the fast rising pulse necessary to make the TDR measurement. Each of the voltage sources has its VALUE attribute defined as: Pulse 0 2 0 25p 10n 1 4 This definition creates a 2 volt rising edge waveform with a rise time of 25ps.
The width and period of the pulse are set to values high enough so that the falling edge of the pulse is not simulated. The source resistance in each circuit has been set at 50 ohms. The simulation of the TDR measurements for each of the three circuits is displayed in the plots below. The simulation has been run for ns.
The waveforms plotted are the voltages between the source resistances and the transmission line inputs. Since the time delay of the transmission line has been specified as 20ns, the reflected waveforms will appear after 40ns since the signal has to travel through the transmission line and back. For a short circuit load, the reflected waveform is equal to the incident waveform but opposite in polarity so that the incident waveform is cancelled when the reflected waveform has propagated back through the transmission line at 40ns.
The middle plot shows the TDR for the open circuit load. For an open circuit load, the reflected waveform is equal to the incident waveform and has the same polarity so that the incident waveform is reinforced when the reflected waveform has propagated back through the transmission line at 40ns. The bottom plot shows the TDR for the matched load. For a matched load, there is no reflected waveform, and the incident waveform is left intact. The amplitude of the reflected waveforms can be used to calculate the impedances of the loads.
This expression can be calculated within the analysis plot using the Formula capability of the analysis text. The following analysis text calculates the load impedance in each of the plots. The formula delimiters have been set as the square brackets, [ ]. Since the incident waveform has a value of 1V in this example, the reflection coefficient can be calculated by measuring the magnitude of the waveform at a specific time and subtracting the incident waveform value to get the magnitude of the reflected waveform.
Subtracting one, which is the magnitude of the incident waveform, returns the magnitude of the reflected waveform. The formula analysis text in each plot correctly displays the value of the corresponding load resistor in the schematic.
The schematic is shown below. The resulting transient analysis is shown below.
CMP 4202 VLSI Systems Design