voltage divider using mos capacitor

[Debdut]

Hello everyone,
I simulated 2 circuits as you can see in the attached image.
My question is how are the mos capacitors acting as voltage divider?
The voltage source for the mos capacitors is sourcing 2.03 µA current. How is that happening?

 

[kemiyun]

Image is hardly clear but I'm assuming that they're series connected capacitors and continue.

The capacitors are acting as voltage divider because the charge that goes through one of them, also goes through the other. Which means that if a certain charge is pushed into these capacitors they're going to store voltages according to their capacitance values. It's Kirchoff's law actually.

The reason that MOScap is sourcing current can be a lot of different things. In general the junctions of the MOSFETs leak current even if they're reverse biased. This current even though it's being sourced or drained from one end of the capacitor, has to be replaced from the supply, because voltage is still constant at both ends. Another reason for the leakage can be gate leakage in smaller tech nodes, but junction is always there that's why I wanted take the safe bet.e

 

[Debdut]

Thanks kemiyun for the reply.
If you click on the image I think it is opening in a new tab of your browser.
I have also used ideal capacitors in contrast to MOS capacitors as you can see in the image, but they are not acting as voltage dividers !!

 

[kemiyun]

Well, I had already done that and it was still small and dark.

Anyway, can you set their initial conditions as 0 and add a series small resistance and run a transient?

The reason I'm asking is because, if there is no charge pushed into these capacitors then they're just going to stay where ever they were. For example this state can be full supply voltage across the terminals of the upper one and 0 volt for the lower one. Since no charge is actually being pushed (because the total voltage on cap stack is the same as voltage supply), nothing changes. This is not the same for the MOScap because unlike ideal elements, MOScap actually leaks, and has a parallel resistor equivalent. So it actually settles at a point where they would share the voltage.

 

[D.A.(Tony)Stewart]

Tolerance for leakage matching and capacitance could be an issue especially during power on.

 

[Debdut]

I simulated the moscap circuit using a pulse waveform varying between 0V and 1V with frequency 1MHz. I have attached the results. The output is from the voltage division point.

 

[FvM]

Not clear what's your problem with the results. The voltage division can't be exactly 1:1 due to substrate capacitance.

 

[Debdut]

FvM - "The voltage division can't be exactly 1:1 due to substrate capacitance."
Can you please explain the operation?

 

[kemiyun]

Dude, it's acting like voltage divider as you wanted them to. I thought that was your question. What do you think is wrong with the results?