Tutorial

Applet Tutorial

In this applet, we present a Single Stage Common Emitter Amplifier. The upper part is the amplifier circuit and lower part is the BJT transistor characteristic curves and the amplifier's input and output waveforms.

The green line in the chracteristic curve is the amplifier's static load line (or DC load line). The gray dot on the DC load line is the amplifier's current operating point. In this ampplet, we can see that given an input waveform, what is the output waveform. Every input point is corresponding to an output point and they form the operating point that should be always on the DC load line.

In this applet, the user can have an overview of how the amplifier waorks and using mouse to drag and change several parameters and see what happens in the amplifier. The user can drag the mouse in the lower part of the applet, i.e. the characteristic curve's part, and the amplifier's parameters will change correspondingly. The new parameters show up in the upper part of the applet, i.e. the circuit part of the amplifier.

[1]. Change the Amplitude: first, we can change the amplitude of the input waveform and see the conrresponding change of the output waveform. Point mous on the upper bond or lower bond of the input waveform yellow area and drag the mouse to change the waveform's amplitude, after the mouse is released we can see the new waveforms on the applet.

[2]. Change the Vcc Value: we can change the Vcc value by point mouse over the cross point where the DC load line and the x-coordinate line meets and drag the mouse see the corresponding Vcc value changes. In the mean time, we can see the new Vcc value in the circuit part.

[3]. Change the Rc Value: we can change the Rc value by point mouse over the cross point where the DC load line and the y-coordinate line meets and drag the mouse see the corresponding Rc value changes. In the mean time, we can see the new Rc value in the circuit part.

[4]. Change the operating point : we can change the operating point by point mouse on the gray dot in the DC load line and drag the mouse see the corresponding operating point changes.

Notice: when the user is going to change the amplifier's parameters out of their correct ranges, the applet will warn the user. For example, soppose we want to change the operating point of the amplifier and we can drag the gray dot on the DC load line to see the corresponding change of the input and output waveforms. But we can not set the operating point too small, otherwise we will enter the sutaration region of the BJT transistor. Hense the output waveform's lower bound (left side) will be distorted and in such a case the applet will show you the minimum lower bond using dashed red line and warns the user. And the applet doesn't allow the user to change the operating point smaller. On the other hand, we can not change the operating point too large, otherwise, the output waveform's upper bond (right side) will greater than Vcc and will be distorted. The same thing will happen when we are trying to change the other parameters, such as the input waveform's amplitude, Vcc and Rc value.