Numerical Example - 6.4.3.5
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Oscillation Frequency Calculation
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Today, we will explore how to design a phase shift oscillator to target a frequency of 1 kHz. Letβs start with the formula related to the frequency of oscillation. Can anyone recall what that formula is?
Is it fβ = 1 / (2ΟRCβ6)?
That's correct, Student_1! Now, if we want to find R given C = 10 nF and fβ = 1 kHz, what should we do?
We can rearrange the formula to solve for R.
Exactly! So, what does the rearranged formula look like?
R = 1 / (2ΟfβCβ6).
Well said, Student_3! Letβs calculate the value of R using that formula. What do we get?
It would be approximately 6497 Ξ©.
And what standard resistor should we use?
6.8 kΞ©!
Correct! So remember, when designing, we round to standard resistor values.
Op-Amp Configuration for Gain
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Now, letβs shift our focus to the op-amp configuration for this oscillator. Who can tell me why gain is important here?
The gain must be set high enough to overcome the feedback networkβs losses.
Correct! We need a gain of at least 29. How can we configure the feedback? Whatβs the relationship?
If we use R_in = 1 kΞ©, then R_f must be at least 29 kΞ©.
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.
Does using higher precision devices help in getting a more stable output?
Absolutely! Precision devices lead to better matching and stability in your oscillator.
Introduction & Overview
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Quick Overview
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 kΞ©. The op-amp needs to be configured for an inverting gain of at least 29 to meet the necessary criteria for oscillation.
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Design of Phase Shift Oscillator
Chapter 1 of 4
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Chapter Content
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
Chapter 2 of 4
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Chapter Content
R=frac12pif_0Csqrt6=frac12pitimes1000textHz times10times10β9textF times sqrt6 R= rac{1}{2 ext{Ο} imes 10^{-5}} imes ext{sqrt{6}} ext{Ξ©} = rac{1}{6.283 imes 10^{-5}} imes 2.449 ext{Ξ©} ext{β } 6497 ext{Ξ©}.
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 Ο (pi) and the square root of 6, ultimately arriving at an approximate resistor value of 6497 Ξ©.
Examples & Analogies
Imagine you are adjusting the gears of a bike. Each gear plays a crucial role in your speed; similarly, here weβre adjusting the resistor to fine-tune the oscillator for optimal performance.
Selecting Standard Resistor Value
Chapter 3 of 4
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Chapter Content
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 Ξ©. The nearest standard resistor value is chosen as 6.8 kΞ©.
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
Chapter 4 of 4
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Chapter Content
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 kΞ©.
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.
Key Concepts
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Oscillation Frequency: The frequency at which an oscillator continuously operates.
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Gain Requirement: Minimum amplification needed in the feedback loop to sustain oscillations.
Examples & Applications
Example 1: Designing a phase shift oscillator with C = 10 nF and targeting fβ = 1 kHz, results in using R = 6497 Ξ©, rounding to 6.8 kΞ©.
Example 2: Set R_f to achieve an inverting gain of at least 29 using R_in = 1 kΞ©, indicating R_f should be approximately 29 kΞ©.
Memory Aids
Interactive tools to help you remember key concepts
Rhymes
To make your oscillator great, ensure gain is high, never wait.
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.
Memory Tools
G.R.E.A.T. - Gain, Resistor, Effective, Adjusted, Target - key steps to design a phase shift oscillator.
Acronyms
ROC - R for Oscillation Calculation.
Flash Cards
Glossary
- Phase Shift Oscillator
An oscillator that utilizes resistive and capacitive networks to produce a phase shift for feedback, essential for generating sustained oscillations.
- Standard Resistor
Commonly manufactured resistor values, standardized for ease of use in electronic circuits.
Reference links
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