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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 look at the small signal model of a current mirror under DC conditions. Can anyone explain what happens to the current mirror in this state?
I think it becomes an open circuit since there's no signal?
Exactly! So, under DC conditions, the network reduces without any signal current, leaving us with a simple resistance representation. This actually simplifies our calculations. Let's remember this using the acronym 'OCC' - Open Circuit Current!
OCC to remember that it's open circuit with no current! Got it!
Now, when we apply a signal current into the current mirror, what do we observe?
The response would be different because it would affect the dependent sources, right?
Right! In this scenario, we need to analyze how the output voltage is influenced by the signal current. So let's keep in mind the phrase 'SIC' - Signal Influences Current to remember the importance of signal impact in our current mirror!
SIC - that makes it clear that we consider signals as crucial variables!
Let's dive into comparing the small signal models of BJTs and MOSFETs. Can someone tell me the key differences?
Is it that BJTs use current sources differently than MOSFETs?
Exactly! MOSFETs rely heavily on voltage dependencies, while BJTs operate based on current. Remember the acronym 'CVC' - Current Varies in BJTs and it helps us recall their dependence on current rather than voltage.
CVC is perfect for remembering how BJT models work!
In practical terms, small signal models demand attention in amplifier circuits. Can anyone give a specific application of these models?
I think they're used in differential amplifiers?
Absolutely! The current mirrors play a vital role in stabilizing bias currents in differential amplifiers. To remember this application, let's use 'ADC' - Amplifier Differential Circuits!
ADC - good for recalling the essential function of current mirrors in amplifiers.
A configuration that allows for a constant current output, useful in various amplifier applications.
Focuses on understanding how circuits behave under small voltage and current changes around a bias point.
Differentiation between direct current (DC) steady states and alternating current (AC) signal conditions.
When DC is here, it’s clear, the circuit goes open, no fear!
Imagine a sleepy circuit under the sun (DC), waking only when AC signals run, to mirror away, current comes to play!
OCC for Open Circuit Current!
SIC for Signal Influences Current – Let this guide your thoughts!
Term
What is a current mirror?
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Term
What does 'small signal analysis' involve?
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A simplification used in circuit analysis that represents a circuit with small AC signals superimposed on a DC bias.
A circuit configuration designed to copy a current through one active device to another, maintaining a constant current regardless of loading.
The steady-state condition in a circuit where no time-varying signals are present.
The phenomenon where the output current of a circuit is a function of the input voltage.
A type of transistor that uses both electron and hole charge carriers.
A type of transistor that uses an electric field to control the flow of current.
This section discusses the voltage dependencies in the small signal model of current mirrors, focusing on both BJT and MOSFET implementations.
The section explores the small signal model of current mirrors used in analog circuits, detailing how voltage influences current behavior in both BJT and MOSFET configurations under DC and AC conditions.
This section elaborates on the vital role of voltage dependency within the small signal model employed in current mirrors. Understanding this model is paramount as it applies to the analysis of analog circuits like amplifiers, specifying both BJT and MOSFET implementations.
The small signal model is particularly crucial when analyzing how current mirrors behave under two scenarios:
The section offers formulas and some nuanced examples to solidify understanding, including how to derive the output voltage as a function of input current, the relevant resistances, and the impacts of non-ideal behaviors inherent in real circuits. Additionally, it lays groundwork for exploring the current mirror's application in various amplifier configurations.