Amplifier BJT User Online Manual
This comprehensive digital guide provides step-by-step instructions for utilizing the Amplifier BJT software suite.
Common-emitter BJT amplifier stage
The circuit diagram of a common-emitter (CE) bipolar junction transistor amplifier stage is shown in Figure 1.
Figure 1 – Common-emitter BJT amplifier stage: a) n-p-n transistor circuit, b) p-n-p transistor circuit
The circuit diagram of a common-emitter (CE) bipolar junction transistor amplifier stage is shown in Figure 1.
Figure 1 – Common-emitter BJT amplifier stage: a) n-p-n transistor circuit, b) p-n-p transistor circuit
1. Selecting a transistor model from the database
Select a transistor model (see Figure 2).Figure 2 – Searching for and selecting a transistor model
Select a transistor model (see Figure 2).Figure 2 – Searching for and selecting a transistor model
Under the label "Input transistor model" type the transistor model name in the input field using Latin characters (case-insensitive), as indicated by the arrow in Figure 2 above. If the model is found in the database, it will be displayed in the list on the left under the label "Model Search" Once the model is found, you can proceed with the preliminary amplifier calculation. Click the "Calculate" button located to the left of the input field, and the program will perform the preliminary calculation of the amplifier stage.
Note to Step 1:
If the model is not found, you can search for transistor equivalents; it is quite possible that they will be available in the software database.
Note to Step 1:
If the model is not found, you can search for transistor equivalents; it is quite possible that they will be available in the software database.
2. Preliminary amplifier stage calculation results
After clicking the "Calculate" button (see Figure 3 below), the software will calculate and display the input and output current-voltage (I-V) characteristics of the selected transistor model. By default, it will select an operating point (Q-point) on the I-V curves, plot the load line, calculate the circuit component values, and determine the main amplifier parameters. The calculation results will appear in the text window under the label"Calculation Results"
Figure 3 – Preliminary amplifier stage calculation results
The amplifier stage calculation is performed in four steps:
1) Calculation of transistor h-parameters at the operating point.
2) DC analysis of the amplifier stage.
3) AC analysis of the amplifier stage.
4) Calculation of the main amplifier parameters.
Note to Step 2:
The software uses color-coding for the I-V characteristics. A total of 10 output characteristic curves are displayed, each marked with a different color. This is required to establish the correlation between the output and input characteristics. Each output curve corresponds to a point of the same color on the input characteristic curve.
1) Calculation of transistor h-parameters at the operating point.
2) DC analysis of the amplifier stage.
3) AC analysis of the amplifier stage.
4) Calculation of the main amplifier parameters.
Note to Step 2:
The software uses color-coding for the I-V characteristics. A total of 10 output characteristic curves are displayed, each marked with a different color. This is required to establish the correlation between the output and input characteristics. Each output curve corresponds to a point of the same color on the input characteristic curve.
3. Final amplifier stage calculation (adjusting calculation parameters)
In the previous step (Step 2), a preliminary calculation of the amplifier stage was performed. For the preliminary calculation, the software uses default parameter settings. For the final calculation, it is necessary to adjust the amplifier parameters to the specific operating mode selected by the user. As an example, let's perform such an adjustment.
The amplifier parameter settings panel is located on the left, as shown in Figure 4.
The amplifier parameter settings panel is located on the left, as shown in Figure 4.
Figure 4 – Amplifier parameter settings panel
Example of setting parameters
For example, suppose we need to calculate an amplifier with a supply voltage of VCC = 24 V (in our case, VCC corresponds to the Vce parameter). In the Vce= input field, set the value to 24 (see Figure 5).
The default Vbe voltage is set to 0.75 V. The Vbe parameter represents the base-emitter voltage, which corresponds to the VJE parameter of the transistor's Spice model. Changing the Vbe value shifts the range of the collector and base currents displayed on the I-V characteristics. In this example, we will leave it unchanged as the value is considered optimal. (However, if you need to calculate an amplifier at low collector operating currents—for instance, Ico = 1 mA—the Vbe parameter should be set lower, e.g., 0.65...0.7 V).
The default Vbe voltage is set to 0.75 V. The Vbe parameter represents the base-emitter voltage, which corresponds to the VJE parameter of the transistor's Spice model. Changing the Vbe value shifts the range of the collector and base currents displayed on the I-V characteristics. In this example, we will leave it unchanged as the value is considered optimal. (However, if you need to calculate an amplifier at low collector operating currents—for instance, Ico = 1 mA—the Vbe parameter should be set lower, e.g., 0.65...0.7 V).
Figure 5 – Setting parameters, recalculating the amplifier with specified settings, and final results in the "Calculation Results" window
Next, the program has automatically selected an operating point of Ico = 27.419m (collector current = 27.419 mA). Suppose we need to calculate the amplifier at an operating point collector current of 20 mA. In the Ico= input field, set the value to 20m (see Figure 5).On the following line, set the lower cutoff frequency. By default, it is set to FL = 10k (10 kHz); we want to change this to 15 kHz. In the FL= input field, set the value to 15k (see Figure 5).
Next, move to the line below to set the load and input signal source parameters. By default, the load resistance is set to RL = 100M (100 MΩ); we want to set it to 200 Ω. In the RL= input field, enter 200 (see Figure 5 below). The internal resistance of the input signal source is set by default to Rs = 0 (0 Ω); we want to set it to 100 Ω. In the Rs= input field, set the value to 100 (see Figure 5).
Now that all calculation settings are configured, click the "Calculate" button again (see Figure 5). The program will then provide thefinal calculation of the amplifier stage.
4. Detailed Solution
This feature is available only in the activated version of the software. When using this feature (see Figure 6), the program generates a detailed (step-by-step) amplifier calculation in Microsoft Word (.docx) format.
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