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{{projectinfo|Tutorial| Analyzing the Frequency Response of Multistage BJT Amplifiers |AnaTUT15 16AnaTUT16 17.png|In this project, you will use the Bode Plotter to simulate the frequency response of BJT amplifiers with different device models.|

*Data Manager*Imported Model Import

|All versions|{{download|http://www.emagtech.com/contentdownloads/project-file-download-repository|ProjectRepo/AnalogLesson13.zip Analog Tutorial Lesson 13|[[RF.Spice A/D]] R15}} }}

In this tutorial you will build and test two-stage common emitter amplifiers using different BJT devices and examine their frequency response. You will learn how to import an external device model and use it in your circuit. You will also become familiar with [[RF.Spice]]'s Bode Plotter virtual instrument.

The voltage source VS is an small-signal AC source with a peak amplitude of 1mV. Let's first take a look at the DC bias of the amplifier. You can run a DC Bias Test of your amplifier to find the operating point [[parameters]] of Q1 and Q2. Or you may simply run a live simulation of your circuit and enable circuit [[animation]] using "Show Voltage Text". The figure below shows the DC voltage at the operating point:

[[File:AnaTUT16 6.png|thumb|750px| The operating point DC voltage voltages in the two-stage common-emitter BJT amplifier.]]

In the previous part, you picked a commercial BJT part from [[RF.Spice]]'s extensive parts database. In many cases, you may need to use a new device model that doesn't already exist in [[RF.Spice]]'s database. You can define a new device model from the ground up, or you may import new device models from external text files. In [[RF.Spice A/D]], a device or part is the combination of a simulation or process model and a symbol. You can build a complete new device and store it to the parts database. You can also use an existing part and simply change the model behind it.  In this part of the tutorial lesson, you are going to import a new BJT model from a text file called "MyNewBJT.TXT". Open a blank text file using any text editor such as Windows Notepad and type in the following text ad save it to the file:

 . model MyBJTModel MyNewBJT npn is = 2.0e-16 bf = 50 vaf = 100 rb = 5 rc = 1 cje = 0.4p  + vje = 0.8 mje = 0.4 cjc = 0.5p vjc = 0.8 ccs = 1p  

 Next, open the [[RF.Spice A/D]] Device Manager using the keyboard shortcut {{key|Ctrl+D}}. Open the menu item '''Menu > File > Import Simulation Model from Text File…''' Follow the instructions on the screen. Enter the model name and a description for your new model such as "New My new NPN-type BJT modelwith better frequency response". Use the [[Windows]] Explorer's Open Dialog to browse your folders, locate the model text file and open it. The program will prompt that your new model has been added to the database.  <table><tr><td>[[File:AnaTUT16 15.png|thumb|550px| Importing the new BJT process model called "MyNewBJT" in RF.Spice's Device Manager.]] </td></tr></table>

Next, go back to the circuit of the previous part. Open the property dialog of the transistor Q1 and click the {{key|New Select Model}} button of that dialog. the Select Model Dialog opens up where you can search for "MyNewBJTModel". Note that the process devices such as BJTs share the same model by default. Therefore, once you change the model of Q1, the model of Q2 will also change and get updated. Run a new live simulation of your circuit to examine its DC bias. As you can see from the figure below, the collector and emitter voltages of both Q1 and Q2 have changed compared to the previous part.

[[File:AnaTUT16 1018.png|thumb|750px600px| The common-emitter amplifierChanging the process model of a BJT device in its property dialog.]]

Get The "Select Process Model" dialog opens up where you can search for "MyNewBJTModel". You can use the frequency response filter and type in the first few letters of your model's name to quickly locate it in the parts database. Highlight the name of your new updated amplifier circuit using the Bode Plotter. Click model and click the {{key|Run sweepSelet}} button and you will see the plot shown in the figure below. Note that the frequency response of the new amplifier has been significantly extended and its 3dB rolloff frequency is now about 4.7MHz with the imported BJT models. Also, note that the gain of the two-stage amplifier has dropped from 80dB to 60dB. This can be explained by replace the fact that the forward beta (bf) parameter of 2N2222 was 150, while the new BJT old model has a reduced value of bf = 50.

[[File:AnaTUT16 1116.png|thumb|750px480px| The common-emitter amplifierImporting the new BJT process model called "MyNewBJTModel".]]

[[File:AnaTUT16 1210.png|thumb|750px| The operating point DC voltage in the two-stage common-emitter BJT amplifierwith "MyNewBJT" process models.]]

[[File:AnaTUT16 1311.png|thumb|750px| The Bode plot of the two-stage common-emitter amplifierusing two "MyNewBJT" process models.]]

[[File:AnaTUT16 1412.png|thumb|750px| The schematic of a two-stage common-emitter BJT amplifierwith shunt series feedback.]]

In the above figure, p(vcc) is Note that the DC power operating point of this circuit hasn't change from the DC power supply VCClast part, while p(rl) because the feedback path is DC-blocked by the power delivered to the loadcapacitor C5. The ratio p(rl)/p(vcc) defines the power efficiency Get a new frequency response of the feedback amplifier. From circuit using the above plots, you Bode Plotter. You can read see from the peak-figure that the frequency response of the feedback amplifier has been further extended to-peak input and output voltages, voltage a rolloff frequency of 13.1MHz but at the expense of a significantly reduced gain and power efficiency:of 39.4dB.

{| border="0"<table>|-<tr>| valign="top"|<td>[[File:AnaTUT16 13.png|-{thumb| class="wikitable"750px|The Bode plot of the two-! scope="col"| RL! scope="col"| Vin(pstage common-p)emitter amplifier with shunt series feedback.]] ! scope="col"| Vout(p-p)! scope="col"| Voltage Gain! scope="col"| I<sub>RL</subtd>(p-p)! scope="col"| P<sub>VCC</subtr>! scope="col"| P<sub>RL</subtable>! scope="col"| Power Efficiency|-| 10k&Omega; | 1686mV | 200mV | 8.43 | 168.5&mu;A | 15.68mW | 71.28&mu;W| 0.46%|-|}

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