Loading the lesson
Loading the lesson
Search AllRounder.ai
Search the courses, subjects, tracks, games and features, or jump straight to a page.
Search the courses, subjects, tracks, games and features, or jump straight to a page.
Learn it your way
A short class with Sarah and her students. The other ways are under More.
Sign up free to listen. Transcripts are free to read.
Today we'll explore how feedback connections affect output resistance in voltage amplifiers. Can anyone tell me why output resistance is important?
It affects how much of the signal gets to the load, right?
Exactly! The lower the output resistance, the better the amplifier can drive a load. Now, we will begin with the ideal situation where the feedback network has infinite input resistance and zero output resistance.
What happens in this ideal case?
In this case, the output resistance can be defined simply by testing with a voltage source. We denote the output resistance as R_out_f and derive it using the relation to the finite input resistance and the gain.
Can you explain the gain A and feedback factor β again?
Certainly! The voltage gain A represents how much the amplifier boosts the voltage, while β is the fraction of the output voltage that is fed back. Is that clearer?
Yes, thank you!
Great! Let's move on to non-ideal conditions.
When we consider non-ideal scenarios, what do you think the effects on output resistance might be?
I guess incorporating resistances like R_s would change the output resistance?
Exactly! A source resistance R_s introduces a voltage drop, which modifies the input voltage seen by the amplifier. Therefore, the output resistance R_out_f would also change.
How do we account for this mathematically?
We can derive an expression for R_out_f in terms of R_s, R_out_β, and other factors. It involves using the concept of voltage division and feedback.
Does that mean if we have more resistance in the system, the output resistance increases?
That's right! More resistance typically leads to greater output resistance, which can affect performance. Let's apply this knowledge to a practical example.
Now let's discuss the feedback network itself. What do you all remember about its role?
It helps stabilize the amplifier and can reduce distortion, right?
Absolutely! A properly designed feedback loop can reduce non-linearities. However, if the feedback network has its own resistance, this also affects our output resistance.
What are the specific changes we should anticipate?
Great question! Introducing R_out_β into our calculations requires adjusting β to account for these losses, often termed as β' and β''. It can seem complex, but we'll solve it through step-by-step analysis.
What if we switch to another configuration like trans-conductance?
That's an excellent point! Each configuration has its own unique characteristics and requires specific formulas. We're entering the part where those variations come into play.
Finally, let’s examine various configurations—like current amplifiers and trans-conductance amplifiers. How do you think their output resistance analysis differs from voltage amplifiers?
Do current amplifiers have different parameters we need to consider?
Exactly! While the foundational concepts remain the same, current amplifiers shift the focus towards current gain, which bears implications on output resistance as well.
I'm curious about how we test the output resistance there.
We'll generally use a similar approach, but the output current and voltage have to be reexamined due to the feedback and sampling choices. Each amplifier introduces nuances worth noting!
So we apply our previous knowledge while adapting to these new configurations?
Exactly! Understanding these adaptations is key to mastering amplifier design and function. Let's wrap up by summarizing our sessions.
We have learned how feedback influences output resistance, the distinctions across amplifier configurations, and the underlying math associated with analyzing these systems.
In amplifiers where feedback flows, lower output resistance shows, driving loads, that's how it grows!
Imagine a gardener watering plants - the feedback helps maintain just the right amount of water, similar to how feedback keeps amplifier performance optimal.
Fabulous Amplifiers Reap Output Success (F.A.R.O.S) - Feedback, Amplifier, Resistance, Output, Stability.
R.A.N. - Resistance Adjusted with Feedback Network.
Term
What is output resistance?
Click to flip
Term
Define feedback.
Click to flip
Term
How does β affect output resistance?
Click to flip
A process where a portion of the output signal is returned to the input of a system to enhance or reduce its performance.
The resistance seen by the load connected to the output of an amplifier, which can vary due to feedback.
The ratio of the output voltage to the input voltage in an amplifier.
The fraction of the output voltage that is fed back to the input.
This section discusses how output resistance is affected in voltage amplifiers due to feedback connections.
The section explains the change in output resistance of voltage amplifiers when feedback is applied, illustrating both ideal and non-ideal scenarios. It provides derivations for output resistance under different conditions, including finite input and output resistances.
In the analysis of voltage amplifiers, the incorporation of feedback can significantly alter the output resistance of the system. Understanding this change is critical for designing effective amplifiers. This section begins by defining the setup for examining output resistance in a voltage amplifier subjected to feedback, particularly using a shunt series feedback configuration.
Initially, we consider an ideal feedback network where the input resistance is infinite, and the output resistance is zero. Under these conditions, the output resistance can be calculated by applying a voltage source at the output and measuring the current, leading to an equation that relates output resistance to the intrinsic parameters of the amplifier: finite input resistance, finite output resistance, voltage gain (A), and feedback factor (β).
As we delve deeper into the analysis, we introduce non-ideal situations, progressively factoring in additional resistances like a source resistance (R_s) and output resistance from the feedback network (R_out_β). Each added element influences the overall output resistance, demanding careful calculations and considerations in the modeling of real-world amplifiers. The section culminates by outlining the equivalent circuitry for varying configurations, such as current and trans-conductance amplifiers, emphasizing how disturbances caused by these factors can be systematically analyzed. This prepares us for subsequent exercises and applications in amplifier design.