Hello everyone I am trying to simulate current starved oscil

Question

Hello everyone I am trying to simulate current starved oscillator which gets its supply voltage from charge pump that get its clock signals from ring oscillator ring oscillator amp charge pump together only are working very well The current starved oscillator works as well when i use a voltage source as supply voltage but when i use the output voltage of charge pump as the supply voltage for current starved oscillator it behaves like this anyone have an idea what could be the problem

Stefan Schippers · Answer

Connect the current starved oscillator to a voltage supply of voltage `Vx` and measure the voltage supply average current `Ix` then connect a resistor of value `Vx Ix` to the output of the charge pump If voltage decays then the simple answer is the charge pump does not output enough current and the current starved oscillator is indeed starving

Stefan Schippers · Answer

If this is the case you can try to reduce the charge pump output resistance by increasing the ringosc frequency or increasing the charge pump capacitors or both

Luis Henrique Rodovalho · Answer

You re using ideal current sources connected to your charge pump output That is why it outputs negative voltages You should never do that As it seems your charge pump can t provide enough power

Luis Henrique Rodovalho · Answer

You could use ideal current sources to a NMOS current mirror and then mirror it to your PMOS biasiing devices This way you won t connect a ideal current source directly to your charge pump

Luis Henrique Rodovalho · Answer

One thing you should do is simulate your current starved oscillator with an ideal supply voltage See which current the supply voltage supplies If you have its voltage and current you can calculate a resistance Use this resistance as a load for your charge pump and see if it still works properly

Amr Samy · Answer

< Luis Henrique Rodovalho> Thanks a lot that was exactly the problem but i still don t understand why the ideal current source degraded the voltage like this

Luis Henrique Rodovalho · Answer

Ideal current sources will make the transistors output a current no matter if it makes sense or not That is why you should use non ideal current sources with a parallel series resistor In this special case by mirroring your biasing current the NMOS tries to output a current to the PMOS which is connected to your charge pump output supply It can t of course so the simulation converges to a point where the NMOS is in the linear region and the current mirror doesn t work as intended Before the ideal current source must have forced the circuit to operate outside the model ranges Maybe all the current from the charge pump went to this single current source Anyway you need a solution You must increase the transistor sizes from the charge pump and the charge pump driver Sooner or later you will find the right dimensions