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A short class with Sarah and her students. The other ways are under More.
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Welcome everyone! Today, let's start with the base current, I_B. Can anyone tell me how we might calculate that?
Isn't it related to the resistance values in the circuit?
Exactly! In a fixed-bias configuration, I_B is often calculated using V_CC and relevant resistances. For our example, I_B is given as 20 µA. Now, can anyone tell me how we use this to find the collector current I_C?
We can use the formula I_C = β * I_B?
Correct! With β = 100, that gives us I_C of 2 mA. Now, let's remember this acronym for these currents: B for Base, C for Collector, and E for Emitter. BC is the core of our amplifier. Let's keep that in mind.
Now, let's move onto small-signal parameters. Can anyone tell me what g_m stands for?
g_m is the transconductance, right?
Exactly! It's calculated as I_C / V_T where V_T is the thermal voltage, often around 26 mV. For I_C = 2 mA, what does this yield for g_m?
That would be around 76.9 mS?
Perfect! Also, r_π is calculated as V_T / I_B, which in our case gives us 1.3 kΩ. Good work bit by bit!
Let’s discuss voltage gain. Who can tell me how we represent voltage gain A_v mathematically?
I think it's -g_m * R_C.
Correct! The negative sign indicates phase inversion. If we substitute in our values, what do we get for our circuit with R_C being 3.3kΩ?
That gives us approximately -200 for the voltage gain!
Exactly! Remember, the voltage gain is critical in amplifier design, reinforcing our BC concept as we look at these calculations.
Now, onto performance parameters. Can someone explain what output swing is?
It's the range of output voltage without distortion, right?
Absolutely! And how do we calculate that?
We look at the DC operating points and how far we can swing before clipping occurs, using the limits of collector voltage.
Exactly! Also, don’t forget power dissipation, calculated as P = I_C * V_CC. Let's keep these key aspects, swing and dissipation, in check!
To wrap up today’s discussions, what have we learned about the CE amplifier?
We calculated voltages, currents, and derived important gain values.
And we also understood the significance of small-signal parameters!
Great! Don't forget the importance of output swing and how power limits can affect our design. Remember, this foundational knowledge serves as our guide for future learning!
The current flowing into the base of the transistor, crucial for determining collector current.
The output current of the transistor which is influenced by base current and the transistor's current gain (β).
The amplification factor of the circuit calculated as a function of transconductance and load resistance.
The range within which the output voltage can vary without a distortion.
The total power lost in the amplifier, calculated based on the operating currents and supply voltages.
In the CE, the base holds sway, I_B helps I_C on its way!
Imagine a race where base current leads, once it crosses the finish, collector current heeds!
B.C.E. - Remember Base current, Collector current, Emitter current for amplifier basics!
C.E.A. - Common Emitter Amplifier helps you remember key elements related to CE amplifiers!
Term
Base Current
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Voltage Gain
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Output Swing
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A type of amplifier configuration that provides significant voltage gain and phase inversion.
The ratio of the output current to the input voltage change in an amplifier, indicating efficiency.
The resistance looking into the base of a transistor amplifier.
This section delves into numerical examples of the Common Emitter Amplifier (CE) with fixed-bias, focusing on calculating gain, input resistance, output resistance, and performance parameters.
In this detailed exploration of the CE amplifier with fixed-bias, the section examines the calculation of the base and collector currents, along with transconductance and small-signal resistances. Further, it illustrates how to derive voltage gain, input and output resistances, and discusses crucial performance parameters like output swing and power dissipation.
In this section, we delve into the numerical analysis of the Common Emitter (CE) amplifier with fixed-bias configuration. The focus is on determining relevant parameters such as gain, input resistance, output resistance, and assessing the amplifier's performance under different operational conditions.
Base and Collector Current Calculation:
I_B is calculated as 20 µA, from which the collector current I_C is derived as 2 mA based on a beta (β) value of 100.Small-Signal Parameters:
g_m and small-signal resistance r_π are defined, with g_m determined using thermal voltage, leading to a calculated resistance of approximately 1.3 kΩ.Voltage Gain Derivation:
A_v, is formulated as -g_m × R_C, with numerical values substituted to yield a final gain of about -200.Input and Output Resistance:
Performance Parameters:
Numerical Calculations:
Finally, the section sets the groundwork for understanding design stability and will explore additional methodologies in upcoming parts.