One of these supported formats is a Matlab matrix file, which can also be read by GNU Octave. I already had an idea of what tools to use the Qucs simulation engine ( qucsator) is a standalone program that reads a text netlist and outputs a text file, so manipulating the input netlist is easy (another advantage of using text format as input format), the outputs can also be easily parsed and moreover the Qucs distribution already includes a qucsconv utility to convert the qucsator simulator results to a variety of formats. Of course optimization, especially by trial and error, is better left to computers, so I started thinking about writing a little script that could automatically write a Qucs netlist, run the Qucs circuit simulator to obtain the circuit performances and then decide on how to update the schematic values to attain the desired goal. Gary points out in his report that he already spent a fair amount of time optimizing the component values and when I tried to further improve the design by trial and error I quickly realized how time consuming the process is and how difficult is to simultaneously improve all the three main parameters (attenuation, input return loss and isolation), since the effect of one component change affects differently all the parameters. Note the very good agreement between the Qucs simulation and the original curves that means the Qucs schematic agrees with the original LTspice schematic.Īt this point I was curious to understand if the design could be improved its performances are already quite good, but there is still some ripple in its attenuation/return loss/isolation curves. In the graphs below the curves in green were obtained from Gary's graphs while the red ones are the actual simulation results with Qucs. Qucs then has also the ability to read text data from a file and convert them into his own dataset format, to be used for further processing. To extract the data from his graphs, I used the nice Engauge Digitizer tool, which allows to quickly obtain a file with all the data in tabular for from an imported graph picture. In his writeup he goes into the details of the design and the effect of the components parasitics, so I won't repeat that here.Īs I usually I use Qucs for simulating my amateur radio RF circuits, I copied the LTspice schematic shown at the beginning of his design report to check if the simulation results were the same also in my environment (otherwise that would very likely mean I made an error while copying the component values and computing their parasitic).Īnd the following picture shows the simulation results, compared with the data show in the graphs of Gary's original writeup. So, as a starting point for my own design I decided to analyze a bit more in detail his design to better understand how the components values influence the bias-tee performances. Its performances seemed quite respectable for a relatively simple circuit, only I was looking for something that could handle some more current. I was looking for a bias-tee to do some measurements on active devices and came across the nice design from Gary Johnson.
0 Comments
Leave a Reply. |