{{projectinfo|Tutorial| Analyzing a Distributed Amplifier Using an Imported RF BJT Model |RF145.png|In this project, the basic concepts of RF.Spice A/D are demonstrated, you will build and test a simple voltage divider is modeled and examineddistributed RF amplifier using your own S-parameter-based BJT model.|
*[[CubeCAD]]RF Amplifier*VisualizationS-Parameter-Based BJT Model*[[EM.Tempo#Lumped Sources | Lumped Sources]]Maximum Gain Design*[[EM.Tempo#Scattering Parameters and Port Characteristics | S-Parameters]] Tuning Stub*[[EM.Tempo#Far Field Calculations in FDTD | Far Fields]] Shunt Open Stub*[[Advanced Meshing in EM.Tempo]] Power Gain|All versions|{{download|http://www.emagtech.com/contentdownloads/project-file-download-repository|ProjectRepo/RFLesson10.zip RF Tutorial Lesson 10|[[RF.Spice A/D]] R15}} }}
=== What You Will Learn ===
In this tutorial you will learn how to import RF BJT models from text files and will build a distributed RF amplifier using a bilateral RF BJT and generic transmission line components.
== Importing High Frequency Transistor Models ==
[[RF.Spice]]'s Parts Database contains a sizable collection of RF diodes and BJTs. As you saw in Tutorial Lesson 8, each S-Parameter BJT model corresponds to a certain DC operating point. Therefore, you will find a large number of RF BJT models associated with the same device but measured at different values of V<sub>CE</sub> and I<sub>C</sub>. The manufacturer data sheets of RF transistors usually contains a table of measured S-parameter data in the following format:
--------
.symbol <symbol_name>
[[File:RFTUT10_9.png|thumb|550px|Creating a new RF BJT device in Device Manager.]]
The first line creates a unique model name in the database, and the second line picks the right symbol, which is usually either "npn_bjt_2port", or "jfet_n" or "mosfet_n" or "mesfet_n", or their p-type counterparts. For this tutorial lesson, you need to create an RF BJT.
----
Create a text file as indicated in the table below. Open [[RF.Spice]]'s Device Manager and select "Create New RF Device from S-Parameter Text File..." from its File Menu. Follow the program's prompts step by step and create your new RF BJT device.
{| class="wikitable"
<math> G_{Tmax} = \frac{|S_{21}|}{|S_{12}|} \left( K - \sqrt{K^2-1} \right) </math>
== Building & Testing a Distributed RF BJT Amplifier== [[File:RF145.png|thumb|640px|The distributed RF BJT Amplifier with generic T-Line components.]][[File:RF144.png|thumb|400px|The property dialog of the imported FR BJT.]]
The following is a list of parts needed for this part of the tutorial lesson:
| AC Voltage Source
| 1V
|-
! scope="row"| NP1
| RF NPN BJT
| Imported Model: MyRFBJT
|-
! scope="row"| XTL1
| 50
|}
----
AC Voltage Source: VS (keyboard shortcut: Alt+V)
Two 50Ω Resistors: RS and RL
RF BJT: MyRFBJT (imported model)
Two Generic T-Line Segments: T1 and T2 (keyboard shortcut: T)
Two Generic T-Line Open Stubs: XTLS1 and XTLS2
Two Ammeters: AM1 and AM2 (keyboard shortcut: Alt+Y)
Two Net Markers: IN and OUT (keyboard shortcut: Alt+N)
----
The goal is to design a distributed BJT amplifier for maximum gain at f = 4GHz. From the S-parameter data of the RF BJT at 4GHz, you find that
Δ = 0.488 ∠-162°
G<sub>Tmax</sub> = 16.7dB;
<table>
<tr>
<td>
[[File:RF144.png|thumb|500px|The property dialog of the imported FR BJT.]]
</td>
</tr>
</table>
The input and output matching networks for this project both consist of a generic 50Ω T-Line segment together with a shunt generic 50Ω T-Line Open Stub as shown in the figurebelow. The lengths of the T-Line Segments and Open Stubs can be found using the same procedure you followed in Tutorial Lesson 3 9 for stub matching. Given λ<sub>0</sub> = 75mm at f<sub>0</sub> 4GHz, these lengths are found to be:
{| class="wikitable"
| T1 || 50Ω || 0.120λ<sub>0</sub> || 9mm
|-
| XTLOS1 XTLO1 || 50Ω || 0.206λ<sub>0</sub> || 19mm 15.45mm
|-
| T2 || 50Ω || 0.206λ<sub>0</sub> || 19mm 15.45mm
|-
| XTLOS2 XTLO2 || 50Ω || 0.206λ<sub>0</sub> || 19mm 15.45mm
|-
|}
Place and connect all the parts as shown in the figure below. Place a net marker called "IN" before the input open stub and place another net marker called "OUT" after the output open stub.
<table><tr><td>[[File:RF148.png|thumb|500px640px|The distributed RF BJT Amplifier without the source and load sections for the purpose of network analysis.]]</td>Place and connect all the parts as shown in the above figure. First, remove the AC voltage source and the source and load resistors to perform network analysis. Run a Network Analysis Test of this circuit with start and stop frequencies set at 3GHz and 5GHz, respectively, with a linear frequency step size of 10MHz. Plot the S-[[parameters]] on an amplitude-only Cartesian graph. The figure below shows the results for s11, s21, s12 and s22 [[parameters]]. It can be seen that the amplifier has a reasonably good return loss at 4GHz. Note that your original S-parameter model of the RF BJT has data for only thee frequencies. {{Note|[[RF.Spice]] interpolates between a model's available frequency data points to calculate the S-[[parameters]] at all the intermediate frequencies. Therefore, a larger number of measured frequency data points leads to more accurate simulation results.}} </tr></table>
Run a Network Analysis Test of your circuit with the parameters specified below:
{| border="0"
|-
| valign="bottomtop"|[[File:RF147.png|thumb-{|900pxclass="wikitable"|left-! scope="row"| Start Frequency| 3G|-! scope="row"| Stop Frequency| 5G|-! scope="row"| Steps/Interval| 10Meg|-! scope="row"| Interval Type| Linear|-! scope="row"| Parameter Set|The graph of magnitude of s11, s21, s12 and s22 parameters of the distributed BJT amplifier circuit.]]S
|-
! scope="row"| Graph Type
| Smith or Cartesian (Amplitude Only) with Decibels checked
|}
The figure below shows the results for S11, S21, S12 and S22 parameters. It can be seen that the amplifier has a reasonably good return loss at 4GHz. Note that your original S-parameter model of the RF BJT has data for only thee frequencies. Using crosshairs you can also read the insertion gain |s<sub>21</sub>| to be 16.7dB as was the design goal.
Next, connect the AC voltage source and the source and load resistors and place the source and load ammeters in {{Note|[[RF.Spice A/D]] interpolates between a similar manner as in model's available frequency data points to calculate the last part of S-parameters at all the previous tutorial lessonintermediate frequencies. SimilarlyTherefore, define a custom output plot called G<sub>P</sub> for the power gain larger number of your amplifier. Use the same definition: G<sub>P</sub> = 20*log10(abs(i(am2)/i(am1))). Run an AC Frequency Sweep Test of your amplifier from 3GHz measured frequency data points leads to 5GHz with linear frequency steps of 10MHz. The figure below shows the graph of power gain vs. frequencymore accurate simulation results. }}
<table>
<tr>
<td>
[[File:RFTUT10_10.png|thumb|750px|left|The graph of magnitude of S11, S21, S12 and S22 parameters of the distributed BJT amplifier circuit.]]
</td>
</tr>
</table>
== Running an AC Frequency Sweep to Compute Power Gain ==
Next, connect the AC voltage source and the source and load resistors and place two ammeters at the source and load ammeters in a similar manner as in the last part of Tutorial Lesson 8. The figure below shows the circuit with the source, load and ammeters:
<table>
<tr>
<td>
[[File:RF145.png|thumb|640px|The distributed RF BJT Amplifier with generic T-Line components.]]
</td>
</tr>
</table>
Similarly, define a custom output plot called "Power_Gain" for your amplifier. Use the same definition: G<sub>P</sub> = 20*log10(abs(i(am2)/i(am1))). Run an AC Frequency Sweep Test of your amplifier according to the table below:
{| border="0"
|-
| valign="bottomtop"|[[File:RF149.png|thumb|900px|left|The graph of the power gain of the distributed BJT amplifier vs. frequency.]]
|-
{| class="wikitable"
|-
! scope="row"| Start Frequency
| 3G
|-
! scope="row"| Stop Frequency
| 5G
|-
! scope="row"| Steps/Interval
| 10Meg
|-
! scope="row"| Interval Type
| Linear
|-
! scope="row"| Preset Graph Plots
| Custom: Power_Gain
|}
The figure below shows the graph of power gain vs. frequency, where you can see the maximum value found to be 16.726dB. This agrees perfectly with you computed insertion gain in the previous part.
<table>
<tr>
<td>
[[File:RFTUT10_11.png|thumb|750px|The graph of the power gain of the distributed BJT amplifier vs. frequency.]]
</td>
</tr>
</table>
<p> </p>
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