Hello, have a question about pnoise simulations noise type time domain.
I have a capacitor that is periodically
- initialized with a starting voltage (with a switch);
- charged with a current source (pMOS)
- and discharged with another switch.
The periodicity of the voltage across the capacitance is 2ns.I made a tdnoise simulation choosing a set of time-points during the voltage ramp across the capacitor. I chose the top plate of the capacitor as output node in the pnoise. The result does not convince me at all. Specifically I have 2 questions:
1) Why the x-axis of the integrated output noise is called "timeindex" and not time? And why it stops at 1.8n, while the pss stops at 2n?
2) The shape of the integrated output noise is not as expected. I expected a step of kT/C noise during the initialization, an increasing noise with a ramp (thermal noise integration) during the voltage ramp and a flat profile during the reset. As you can see in the picture below (pink=voltage across the capacitor, green=integrated noise), the green curve stays flat during the voltage ramp.
I upload also my settings for the pss and pnoise.
Thanks a lot for any feedback!