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Ampitude in LC VCO is going above supply

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niteshtripathi

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Hi all,

In LV VCO, the output amplitude is going above suppy. What is the proper reason behind this. Please help me on this.

Thanks & Regards,
Nitesh
 

Hi,

More details please.
Circuit, measured values, measurement conditions, measurement equippment.

With the given informations I assume it's just a measurement error. Just guessing ... all we can do for now.

Klaus
 

LC vco. I guess LC means inductor & capacitor?
In a resonating circuit (LC tank circuit) it's possible for oscillations to build to large voltage swings. Amplitude can become greater than supply voltage.
 

BradtheRad said:
LC vco. I guess LC means inductor & capacitor?
In a resonating circuit (LC tank circuit) it's possible for oscillations to build to large voltage swings. Amplitude can become greater than supply voltage.
Click to expand...

Yes, I means the same as you stated. Can you please elaborate it, How? any mathematical derivation. Thanks alot for your valuable time.
 

Take the example of the attached LC oscillator shown below.
DC voltage across an inductor HAS to be zero.
On one side of the inductor L1, you have Vdd. On the opposite terminal, you need to have on average Vdd else there will be a DC voltage across the inductor. If you have a swing on that node of the inductor, it must both go up and below Vdd to maintain an average Vdd.
lc_oscillator.jpg
 

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