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RING OSCILLATOR PUZZLE

By Admin on

Ring Oscillators are very commonly used circuits in SoCs, where they find their use in Voltage Controlled Oscillators used inside the PLLs, and also used as Silicon odometer circuits- which are used to track various parameters of the device like variation of timing with ageing etc.

It is also a well-known fact that ring oscillators have odd number of inverters connected in form of a chain, as shown below:



And the frequency of oscillations is given by the expression:

f = 1/(2NT)

N= Number of inverters (odd)

T= Propagation delay of a single inverter

Can you comment on the below circuit? Maybe an expression for it's oscillation frequency? Or perhaps any analytical expression (without bothering about the intricacies of various transistor parameters) for the voltage? Assume the operating voltage to be 1V.


Please post your answers here. I'd be happy to share the solution and my thought process in a couple of days.



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