Charge Pumps -Query - Ripple Vs Switching Frequency

Thread Starter


Joined Oct 31, 2011
Hi Folks,

I tried designing a Dickson's charge pump using diode connected MOSFET.
Here are the below observations:

For a voltage doubler:

When W=240nm, charge pump capacitance= load capacitance= 1p F, load resistance= 10M ohm, Switching frequency=500k Hz, Vin=2V


Vout= 4.3772V, settling time= 50u s (4.3366V).
Here settling time refers to time at which output have a constant value.

1. I tried to increase the switching frequency to 500M Hz, peak of output voltage ripple is slightly decreasing.

2. Decreasing the load resistance resulted in the increase of output ripple.
3. When I try to lower the switching frequency, the load resistance required to have reasonable output is increasing.

4. With constant load resistance: if load capacitance increases then settling time increases and ripple decreases but output is same.
5. With constant load capacitance: if load resistance decreases then output decreases and ripple increases but settling time is same.

6. with an increase in the charge pump capacitance, settling time and output voltage decreases.

7. With an increase in 'w' of nmos : best results are coming for 240n M for all the frequencies. I assumed that the with the increase in 'W', best results will come. But best results are coming for 240nm width.

Can you explain me the reason behind all the seven observations?