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|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:

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 "My new NPN BJT model with 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.

[[File:AnaTUT16 18.png|thumb|550px600px| Changing the process model of a BJT device in its property dialog.]]

[[File:AnaTUT16 10.png|thumb|750px| The operating point DC voltage in the two-stage common-emitter BJT amplifierwith "MyNewBJT" process models.]]

[[File:AnaTUT16 11.png|thumb|750px| The Bode plot of the two-stage common-emitter amplifierusing two "MyNewBJT" process models.]]

Note that the DC operating point of this circuit hasn't change from the last part, because the feedback path is DC-blocked by the capacitor C5. Get a new frequency response of the feedback amplifier circuit using the Bode Plotter. You can see from the figure that the frequency response of the feedback amplifier has been further extended to a rolloff frequency of 13MHz 13.1MHz but at the expense of a significantly reduced gain of 39dB39.4dB.

[[File:AnaTUT16 13.png|thumb|750px| The Bode plot of the two-stage common-emitter amplifierwith shunt series feedback.]]

[[File:AnaTUT16 14.png|thumb|750px| The common-emitter amplifierBode plot exported to a graph in RF.Spice's Data Manager.]]

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