Numerical Example - 6.4.3.5 | Module 6: Oscillators and Current Mirrors | Analog Circuits
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6.4.3.5 - Numerical Example

Practice

Interactive Audio Lesson

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Oscillation Frequency Calculation

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0:00
Teacher
Teacher

Today, we will explore how to design a phase shift oscillator to target a frequency of 1 kHz. Let’s start with the formula related to the frequency of oscillation. Can anyone recall what that formula is?

Student 1
Student 1

Is it f₀ = 1 / (2πRC√6)?

Teacher
Teacher

That's correct, Student_1! Now, if we want to find R given C = 10 nF and f₀ = 1 kHz, what should we do?

Student 2
Student 2

We can rearrange the formula to solve for R.

Teacher
Teacher

Exactly! So, what does the rearranged formula look like?

Student 3
Student 3

R = 1 / (2πf₀C√6).

Teacher
Teacher

Well said, Student_3! Let’s calculate the value of R using that formula. What do we get?

Student 4
Student 4

It would be approximately 6497 Ω.

Teacher
Teacher

And what standard resistor should we use?

Student 1
Student 1

6.8 kΩ!

Teacher
Teacher

Correct! So remember, when designing, we round to standard resistor values.

Op-Amp Configuration for Gain

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0:00
Teacher
Teacher

Now, let’s shift our focus to the op-amp configuration for this oscillator. Who can tell me why gain is important here?

Student 2
Student 2

The gain must be set high enough to overcome the feedback network’s losses.

Teacher
Teacher

Correct! We need a gain of at least 29. How can we configure the feedback? What’s the relationship?

Student 3
Student 3

If we use R_in = 1 kΩ, then R_f must be at least 29 kΩ.

Teacher
Teacher

Good understanding, Student_3! So to ensure oscillation, we need to make sure that the ratio of R_f/R_in is greater than or equal to 29.

Student 4
Student 4

Does using higher precision devices help in getting a more stable output?

Teacher
Teacher

Absolutely! Precision devices lead to better matching and stability in your oscillator.

Introduction & Overview

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Quick Overview

This section provides a numerical example for designing a phase shift oscillator with a specified frequency.

Standard

The section illustrates the design process of a phase shift oscillator to achieve a target frequency of 1 kHz using specified resistor and capacitor values, including practical implementation with standard resistor values.

Detailed

Detailed Summary

In this section, a numerical example is given to design a phase shift oscillator targeting an oscillation frequency of 1 kHz. The design process begins with the formula derived from the phase shift oscillator configuration, which states that the oscillation frequency is given by:

$$f_0 = \frac{1}{2\pi RC \sqrt{6}}$$

As specified, the capacitor value is given as C = 10 nF. To find the required resistor value R, we rearrange the formula to obtain:

$$R = \frac{1}{2\pi f_0 C \sqrt{6}}$$

Substituting the known values, we calculate R and find a standard resistor value of approximately 6.8 kΩ. The op-amp needs to be configured for an inverting gain of at least 29 to meet the necessary criteria for oscillation.

Audio Book

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Design of Phase Shift Oscillator

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Design a phase shift oscillator using an op-amp for f_0=1textkHz. Let C=10textnF.

Detailed Explanation

In this chunk, we are tasked with designing a phase shift oscillator for a target frequency of 1 kHz, using a capacitor value of 10 nF. The aim is to determine the required resistor value to achieve this frequency in the oscillator design.

Examples & Analogies

Think of this task as tuning a musical instrument. Just as a musician adjusts the tension of strings to set the correct pitch, here we are adjusting the value of resistors to set the correct frequency for our oscillator.

Calculating Resistor Value

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R=frac12pif_0Csqrt6=frac12pitimes1000textHz times10times10−9textF times sqrt6 R= rac{1}{2 ext{π} imes 10^{-5}} imes ext{sqrt{6}} ext{Ω} = rac{1}{6.283 imes 10^{-5}} imes 2.449 ext{Ω} ext{≈ } 6497 ext{Ω}.

Detailed Explanation

To find the required resistor value (R), we use the formula which incorporates the frequency (f_0) and the capacitance (C). The values are plugged into the formula, which includes π (pi) and the square root of 6, ultimately arriving at an approximate resistor value of 6497 Ω.

Examples & Analogies

Imagine you are adjusting the gears of a bike. Each gear plays a crucial role in your speed; similarly, here we’re adjusting the resistor to fine-tune the oscillator for optimal performance.

Selecting Standard Resistor Value

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Use standard resistor value R=6.8textkOmega.

Detailed Explanation

After calculating the required resistance, we select a standard resistor value that is close to our calculated value of 6497 Ω. The nearest standard resistor value is chosen as 6.8 kΩ.

Examples & Analogies

Choosing a standard resistor value is like picking a size in clothing: you might not find the exact fit you calculated, but you select the closest standard size available.

Amplifier Gain Configuration

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The op-amp should be configured for an inverting gain of at least 29. If using feedback resistors R_f and R_in (for the op-amp input), A_v=R_f/R_in. So, R_f/R_in ge 29. If R_in=1textkOmega, then R_fge 29textkOmega.

Detailed Explanation

In this step, we determine that the op-amp must be configured to provide a specific gain (A_v) of at least 29 to ensure stable oscillation. We express this gain in terms of feedback resistors R_f (feedback resistor) and R_in (input resistor) and calculate the minimum necessary resistance for R_f when R_in is set to 1 kΩ.

Examples & Analogies

Think of the op-amp like a microphone amplifier. If you're trying to capture soft sounds, you may need to boost the volume significantly; here, we are setting our resistors to ensure that our oscillator can maintain sufficient 'volume' or gain to work properly.

Definitions & Key Concepts

Learn essential terms and foundational ideas that form the basis of the topic.

Key Concepts

  • Oscillation Frequency: The frequency at which an oscillator continuously operates.

  • Gain Requirement: Minimum amplification needed in the feedback loop to sustain oscillations.

Examples & Real-Life Applications

See how the concepts apply in real-world scenarios to understand their practical implications.

Examples

  • Example 1: Designing a phase shift oscillator with C = 10 nF and targeting f₀ = 1 kHz, results in using R = 6497 Ω, rounding to 6.8 kΩ.

  • Example 2: Set R_f to achieve an inverting gain of at least 29 using R_in = 1 kΩ, indicating R_f should be approximately 29 kΩ.

Memory Aids

Use mnemonics, acronyms, or visual cues to help remember key information more easily.

🎵 Rhymes Time

  • To make your oscillator great, ensure gain is high, never wait.

📖 Fascinating Stories

  • Imagine a clever engineer who uses capacitors and resistors to craft the perfect phase shift oscillator for his project, securing the desired frequency while sticking to standard values.

🧠 Other Memory Gems

  • G.R.E.A.T. - Gain, Resistor, Effective, Adjusted, Target - key steps to design a phase shift oscillator.

🎯 Super Acronyms

ROC - R for Oscillation Calculation.

Flash Cards

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Glossary of Terms

Review the Definitions for terms.

  • Term: Phase Shift Oscillator

    Definition:

    An oscillator that utilizes resistive and capacitive networks to produce a phase shift for feedback, essential for generating sustained oscillations.

  • Term: Standard Resistor

    Definition:

    Commonly manufactured resistor values, standardized for ease of use in electronic circuits.