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A short class with Sarah and her students. The other ways are under More.
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Today we will explore the current mirror and its significance in designing common emitter amplifiers. Can anyone tell me what a current mirror does?
Isn't it used to provide a constant current regardless of the load?
Exactly! So when we use it in an amplifier, it helps maintain a steady current through the active load. Now, how do we ensure that transistors are matched?
I think we have to use identical transistors, right?
Correct! Using identical transistors ensures balanced performance. Now, let’s discuss biasing resistances.
What happens if the resistances aren't matched?
Great question! Mismatched resistances can result in unequal current flow, affecting amplifier stability. Let’s summarize: current mirrors help provide a constant current and require matched components for optimal performance.
In our example, we wanted both collector current I_C1 and I_C4 to be equal. How do we calculate the required bias resistance?
We need to make sure the base currents are equal, right?
Yes, we can ignore the base current losses if we assume high beta. Can anyone remind me of the required current flow for our example?
The current was supposed to be 2 mA?
Correct! And to achieve this with a β of 100, we calculated resistance values to maintain that current. Now, what's the significance of the Early voltage?
Isn't it to account for variations in the output characteristic?
Exactly! The Early voltage ensures our calculations remain accurate by accounting for non-idealities. Let’s reaffirm this lesson; matching parameters is critical for stability in electronic circuits.
Now, let’s dive into computing the voltage gain of our amplifier. Our derived voltage gain was about 1923. Can anyone explain why high gain is expected here?
Because of the active load design, it significantly boosts the voltage!
Absolutely! High output resistance aids in achieving that high voltage gain. Now, let's differentiate between DC output voltage and AC signals.
Does the DC output voltage change with the collector current?
Exactly! If our transistors are mismatched, it can lead to a voltage drop, requiring us to lower our output voltage. Does anyone recall what our final output voltage was?
Wasn't it 11.4 V before considering mismatches?
Right! It’s crucial to take those deviations into account in practical designs. Remember, accuracy in current reflection determines overall performance.
In a current mirror, currents reflect, maintaining stability is what we expect.
Imagine twin brothers performing the same task. One mirrors the movements; the other follows exactly, ensuring harmony.
MEMO for Current Mirroring: Maintain Equal Matching Output.
EASY - Early voltage, Active load, Stability in yield.
Term
What is a current mirror?
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Term
Define voltage gain.
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Explain Early voltage.
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An electronic circuit that copies the current flowing in one active device to another, maintaining accurate current levels.
A type of amplifier configuration that provides significant voltage gain from an input signal.
The current gain factor of a transistor; the ratio of collector current to base current.
A measure of the efficiency of a transistor's output characteristics; factored into voltage gain calculations.
The direct current voltage output from a circuit after accounting for losses.
The ratio of the output voltage to the input voltage in an amplifier.
The resistance seen by the load connected to the output of an amplifier.
This section elaborates on the use of current mirrors in common emitter amplifiers, exploring numerical examples and their outcomes.
It delves into the concept of current mirrors applied in common emitter amplifiers, illustrating the theory with practical numerical examples that entail calculations of resistances, collector current, small signal output resistance, voltage gain, and the significance of early voltage. The section serves as a precursor to applying these concepts in differential amplifiers.
This section focuses on the application of current mirrors within common emitter amplifiers, using practical numerical examples to better understand the design and analysis of these circuits. The lecture introduces concepts such as the current through each transistor, the necessity for matched transistor characteristics, and the calculations needed for biasing resistances and output voltages. The determinants of small-signal output resistance and voltage gain are explored as well, emphasizing the importance of precision in current mirroring to maintain circuit performance. The section aims to provide stepping stones towards more complex applications such as differential amplifiers, preparing students for a deeper understanding of electronic circuit design.