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Message started by zahramoh on Feb 2nd, 2022, 8:56am

Title: voltage regulation
Post by zahramoh on Feb 2nd, 2022, 8:56am

I am designing a digital temperature sensor using a ring VCO. The supply voltage is 1.2V and should be constant without any changes due to noise or other parameters. How can I have this constant supply voltage?

Title: Re: voltage regulation
Post by Geoffrey_Coram on Feb 10th, 2022, 1:55pm

Noise will certainly change the voltage, and as the VCO operates, it will pull different amounts of current from the supply, which will cause fluctuations.

I think you probably need to decide how much fluctuation you can tolerate, and then design the voltage regulator (LDO) to do better.

Title: Re: voltage regulation
Post by Horror Vacui on Mar 14th, 2022, 7:42am

You need a regulator with zero ohm output impedance, and/or an infinite capacitance at the supply. Or at least try to achieve a performance which mimics these ideal conditions.

The current fluctuations in your circuit -- if it's a digital ring VCO, there will be current spikes for every transition -- will drop a voltage on the output impedance of your regulator. A regulator typically has a feedback loop and the regulator is effective only within the bandwidth of this loop. At frequencies above that you can combat voltage droops with a low ESR capacitor on your supply. If the cap is small, then charges/current taken from it will drop its voltage. The current from it will drop a voltage through its ESR.

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