Oscillator Frequency of a Ring Oscillator with RC feedback

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SUMMARY

The discussion focuses on the operation of a ring oscillator with RC feedback, specifically addressing the charging and discharging behavior of the capacitor in the circuit. The user references a similar circuit from Gadgetronix, which utilizes logic gates to generate square waves. Key concerns include the impact of the voltage divider rule across the RC components and the differences in component values between the two circuits. The user concludes that the circuit may not function as intended due to the low input impedances of TTL gates, suggesting that CMOS components like the 74Cxx or RCA 4000 series are more suitable for this application.

PREREQUISITES
  • Understanding of ring oscillator circuits
  • Knowledge of RC timing circuits
  • Familiarity with TTL and CMOS logic families
  • Basic principles of voltage dividers
NEXT STEPS
  • Study the operation of CMOS ring oscillators using 74Cxx series components
  • Research the voltage divider rule in RC circuits
  • Explore the frequency calculation for RC oscillators
  • Examine the differences between TTL and CMOS logic gate characteristics
USEFUL FOR

Electronics engineers, hobbyists designing oscillators, and students studying digital circuit design will benefit from this discussion.

jaus tail
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Homework Statement
What is frequency of oscillator in below circuit?
Relevant Equations
f = 1/(2*3.14*R*C)
246515

I'm not sure how will this oscillator work. Assume A is low, so B will be high and the capacitor will charge through B-C- 2Mohm.
Now even D has gone high, so A will be high and B will be low and C will discharge. I'm not sure how the voltage divider rule across RC will take into effect.
I found a similar structure in this link (3rd circuit diagram):
https://www.gadgetronicx.com/square-wave-generator-logic-gates/Ref: Gadgetronix Square Wave Generator Using Logic Gates. But I'm not sure how if the two circuits will work same as position of Capacitor is after 2nd inverter in the diagram in link.

How will the C charge and discharge here?
 
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The circuit from your link has different component values, and lists an equation for the frequency of oscillation. I haven't tried this type of oscillator before, so I need to think a bit more about it to understand how it works...

1563554875766.png
 
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Since these are TTL gates with fairly low input impedances I doubt this circuit would work. I think you'd have to pull pretty hard voltage-wise to get the input to go low, like maybe -50V thru a 50K resistor to produce 1mA fan-in.

Probably intended for CMOS like 74Cxx or rca 4000 series.
 
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Likes jaus tail and Tom.G

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