In this tutorial you will build an RF amplifier using a high frequency bipolar junction transistor (BJT) with lumped elements. First, you will examine the S-parameter model of the transistor and analyze its DC bias circuit. Then, you will calculate the port characteristics of the amplifier and verify its matching networks. Finally, you will run an AC frequency sweep analysis of the amplifier to characterize its voltage and gain performance.
== Examining the Comparing High Frequency & Low Frequency BJT Model Models ==
High frequency transistors are typically characterized by their S-[[parameters]]. The manufacturer data sheets of RF transistors usually contains tables of measured S-parameter data for various DC bias operating points over a certain range of frequencies. [[RF.Spice]] has a large number of RF bipolar junction transistor (BJT) models with measured S-parameter tables for different combinations of collector-emitter voltages (VCE) and collector currents (IC). Most of [[RF.Spice]]'s RF BJT devices also have counterpart standard BJT model that can be used for DC operating point analysis. The figures below shows the property dialog of the standard BJT model of BFG193 next to the property dialog of the RF BJT model of BFG193 measured at VCE = 10V and IC = 10mA. You will use this transistor for the amplifier design of this tutorial lesson.
[[File:RF120.png|thumb|300px|The basic BJT RF circuit.]]
You will start this tutorial lesson by testing the S-[[parameters]] of BFG193. Open the Parts Bin of the Toolbox and search for BFG193. You can search alphabetically or by function under Active > Transistor > NPN > RF. Place an instance of this BJT on the schematic and place two Net Markers (keyboard shortcut: Alt+N) to designate the base and collector of the BJT as the input and output of your circuit as shown in the opposite figure. Ground the emitter of the BJT. Run a Network Analysis Test of your simple two-port RF circuit. Set the start and stop frequencies of the sweep to 500MHz and 1500MHz, respectively, with a linear frequency step size of 10MHz. Choose "S" [[parameters]] on a Cartesian graph with both amplitude and phase and a dB scale. The figure below shows the S-parameter results with magnitudes in dB and phases in degrees. Use the tracking crosshairs of the graph window to read the value of |s21| at 1GHz. The reading at the bottom of the screen shows a value of 12.442dB, which corresponds to 4.187 as you can see from the highlighted row in the S-parameter table of the BJT's property dialog.
== Examining the High Frequency BJT Model ==
{{Note|The symbols You will start this tutorial lesson by testing the S-[[parameters]] of BFG193. Open the standards BJT Parts Bin of the Toolbox and its search for BFG193. You can search alphabetically or by function under Active > Transistor > NPN > RF counterpart with . Place an S-parameter model are slightly differentinstance of this BJT on the schematic and place two Net Markers (keyboard shortcut: Alt+N) to designate the base and collector of the BJT as the input and output of your circuit as shown in the opposite figure. Ground the emitter of the BJT.}}
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[[File:RF120.png|thumb|300px|The basic BJT RF circuit.]]
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{| border="0"|Run a Network Analysis Test of your simple two-| valign=port RF circuit. Set the start and stop frequencies of the sweep to 500MHz and 1500MHz, respectively, with a linear frequency step size of 10MHz. Choose "bottomS"|[[File:RF119parameters]] on a Cartesian graph with both amplitude and phase and a dB scale.pngThe figure below shows the S-parameter results with magnitudes in dB and phases in degrees. Use the tracking crosshairs of the graph window to read the value of |thumbs21|900px|left|Graph at 1GHz. The reading at the bottom of magnitude and phase the screen shows a value of s1112.442dB, s21, s12 and s22which corresponds to 4.187 as you can see from the highlighted row in the S-parameters parameter table of BFG193 over the frequency range 500MHz - 1500MHzBJT's property dialog.]]|-|}
{{Note|The symbols of the standards BJT and its RF counterpart with an S-parameter model are slightly different.}}
== Building the BJT Amplifier <table><tr><td>[[File:RF119.png|thumb|750px|left|Graph of magnitude and Its DC Bias Circuit ==phase of s11, s21, s12 and s22-parameters of BFG193 over the frequency range 500MHz - 1500MHz.]]</td></tr></table>
[[File:RF110.png|thumb|640px|The RF == Building the BJT Amplifier with standard BJT model for and Testing Its DC bias analysis.]]Bias Circuit ==
The following is a list of parts needed for this part of the tutorial lesson:
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<table><tr><td>[[File:RF111RF110.png|thumb|250px640px|The results of DC Bias Test of the RF BJT Amplifier using BFG193's with standard BJT Modelmodel for DC bias analysis.]]</td></tr></table>
Place and connect all the parts as shown in the above figure. Note that for this part you will use the standard BJT model with the "Ideal Forward Beta (BF)" parameter. You need the standard model to perform a DC operating point analysis. The resistors R3 and R4 acts as a voltage divider for power supply VCC. R5 and R6 control and determine the collector and emitter currents, respectively. The RF chokes L3, L4 and L5 pass the DC currents but block the AC signal and effectively remove the resistors R3, R4 and R5 from the RF analysis. The bypass capacitor C3 shorts the resistor R4 in the AC analysis. The DC blocking capacitor C4 isolates the DC bias circuitry form the load but acts as a short circuit for AC analysis. Note that for this circuit, the tuning capacitor C2 also acts as a DC blocking capacitor which isolates the bias circuitry from the AC source.
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[[File:RF111.png|thumb|300px|The results of DC Bias Test of the BJT Amplifier using BFG193's standard BJT Model.]]
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The DC bias circuit has been designed to generate a collector current of IC = 10mA with a collector-emitter voltage of VCE = 10V. For this reason, you will use the S-parameter RF model BFG193v10v10mA in the next part. Run a DC Bias Test of your BJT amplifier to find its DC operating point [[parameters]]. From the results table, you will see:
I<sub>C</sub> = 10.087mA
V<sub>CE</sub> = V<sub>QC</sub> - V<sub>QE</sub> = 16.933 -6.911 = 10.022V
which validate the DC bias design goals. You can also see all the DC voltages and currents by running a live simulation of the circuit and enabling circuit [[animation]] on the [[Schematic Editor]].
== Stability Analysis of the BJT Transistor & RF Design Strategy ==