# Negative Charge Pump- How to analyze this?

I am using CMOS 4069 inverter and wired up this circuit. I want to generate a $-V_{dd}$ negative pulse and $2V_{dd}$ positive pulse. The circuit above is for the negative voltage. However, I get really low negative voltage. In the analysis of the circuit, I couldn't get about the on-off regions of the mosfet when the square wave is sent. Could anyone help me with the analysis? Another small question - shouldn't $V_A$ and $V_B$ be negative for the MOSFETs to be in ON-region? Thank you.

• Such charge pumps are always going to have a volt drop on each conversion stage. That circuit looks like a pump and active rectifier in one. What voltage are you running the 4069 at, what current are you drawing from the -ve rail? – KalleMP Feb 20 '16 at 22:02
• @KalleMP I am giving an input voltage of Vdd=5V and getting a negative voltage output of -0.5V approximately. Current... I didn't measure, I will measure and tell you. – Win Vineeth Feb 21 '16 at 0:39
• If you have no load you should get 'close' to your specified voltage. The type of charge pump I have dealt with is similar to the one at the link eeweb.com/blog/extreme_circuits/… You rearrange the diodes to select negative voltage. Your circuit might even be 'isolated' and could have a different ground reference because the power is fed through two capacitors, kind of neat but needs caps twice as large. – KalleMP Feb 22 '16 at 20:52
• The Wikipedia article may have some ideas, they show how to chain these isolated circuits to increase the pumped voltage en.wikipedia.org/wiki/… – KalleMP Feb 22 '16 at 20:52