![]() ![]() Dropping by ten times is a reduction of 20 dB hence, the slope is 20 dB per decade. What does this mean you might ask? It basically means that at a frequency well above the -3 dB point, if frequency rises by (say) ten times, the output amplitude drops by 10 times. The roll-off slope is 20 dB/decade for a single order low pass filter. The -3dB point or do I do something else? How do I get the roll-off slope - do I just calculate the gradient at In other words, think outside the box a little.īy definition, the -3dB frequency is when the output power is half the input power. You shouldn't limit yourself to what the bode plot phase response is limited to. I think you can see that at DC the gain is unity and the phase angle is 0 °.Īt high frequency, it's really asking you what the gain is at infinite frequency and that has to be zero but, the phase is clearly -90 °. You can change the number of figures shown for the optimized values in the optimization dialog by right-clicking on the "initial" table header and selecting the "Set precision" menu, as shown in the following figure.įigure 10 - Changing the displayed variables precision.I just performed an AC Simulation on QUCS and was asked to find values In case you need to do further modifications to the schematic, the optimization component can now be disabled and the optimized values from the pasted equation will be used. The resulting schematic will be as shown in the next figure.įigure 9 - Schematic with optimized values. They are now the initial values for each one of introducedīy clicking the "Copy current values to equation" button, an equation component defining all the optimization variables with the values of the "initial" column will be copied to the clipboard and can be pasted to the schematic after closing the optimization dialog. The best found circuit sizes can be found in the optimization dialog, in the Seconds on a modern computer, the best simulation results is shown in the The last step is to run the optimization, i.e. The resulting schematic is show in Figure 6. The next step is to change the schematic, and define which circuit elements are Them into a single cost function, that is then minimized.įigure 5 - Optimization dialog, goals options. Identifiers placed into properties of components and not the components'įigure 4 - Optimization dialog, variables options.įinally, go to Goals where the optimization objective (maximize, minimize) andĬonstraints (less, greater, equal) are defined. In the Variables tab, defining which circuit elements will be chosen from theĪllowed range, as shown in Figure 4. Over- or underestimationĬan lead to a premature convergence of the optimizer to a local minimum or, a very longįigure 3 - Optimization dialog, algorithm options. Iterations', 'Constant F' and 'Crossing over factor'. From theĮxisting parameters, special attention should be paid to 'Maximum number of ![]() Now, open the optimization component and select the optimization tab. The schematic from Figure 1 and change it until you have the resulting schematic ![]() To setup a netlist for optimization two things must be added to the alreadyĮxisting netlist: insert equation(s) and the optimization component block. Optimization problem as a composition of functions, leading in this case to the It can either be the delay or the rise time of a digital circuit, or Optimization of a circuit is nothing more than the minimization of a costįunction. Before using this functionality, ASCO must be installed For circuit optimization, Qucs uses the ASCO toolīrief description on how to prepare your schematic, execute and interprete the
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