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Hello Mr. Setsuda,

I have a question about theory of Charge Injection effects in Switching Capacitor Circuits based on MOSFET.
Could you tell me if the voltage across the load (or hold) capacitor in a Switched Capacitor circuit, cause of Charge Injection effect, during the falling time of the gate command voltage of the switch (suppose that it is a pulse generator voltage which goes from 5V (high) to 0V (low)), increases or decreases? Thank you

Hello Emanueie Cuoccio san

Thank you for your question.

I am not familar Charge Injection effects.

My understanding of your question is

1)When MOS-FET switch off,

2)Capacitor support MOS-FET.

3)Then current goes into MOS-FET

4)Charge injection effect is happened.

5)Then Capacitor Voltage is increase or decreases?

is my understanding correct?

Please confirm and reply.

Sorry for my not enough knowledge,

I will try to do my best.

Thanks
Setsuda

Hello Emanueie Cuoccio san

Thank you for your question.

I am not familar Charge Injection effects.

My understanding of your question is

1)When MOS-FET switch off,

2)Capacitor support MOS-FET.

3)Then current goes into MOS-FET

4)Charge injection effect is happened.

5)Then Capacitor Voltage is increase or decreases?

is my understanding correct?

Please confirm and reply.

Sorry for my not enough knowledge,

I will try to do my best.

Thanks
Setsuda

Yes Mr. Setsuda. Your understanding is correct. I've read that if you measure the voltage across the capacitor along time, you notice that during the falling time of the gate voltage wave there is a spike of voltage in the capacitor's waveform. I want to know if it's correct that this spike is negative (and so there is a sudden decrease of voltage across the capacitor). I've thought that it may be correct if you think that the charge into the channel of the FET moves leaves the channel moving partially towards the generator, and partially towards the capacitor during the switching off of the MOSFET. So that additive negative charge that flows onto capacitor could be considered as cause of a decrease of the voltage across it. Don't worry if it's not your field of study. I have to thank you anyway for your helpfulness. Best regards.      EC

Hello Emanuele Cuiccio san

Thank you for your reply.

Unfortunately I am not familiar about this matter.

So I asked my old connection about power supply related engineer and got advice below from him.

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this question is really not easy. I’m not really sure if I understood it correct. Assuming that the below circuit is correct understanding the voltage of the output C should be decreased. When switching off the MOSFET the gate has to be discharged and this charge should go into the Cload. Means the voltage should decrease.

Hope this help and my answer is fitting to the question ;-)

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Please refer above.

I am afraid to say that

It is not easy for me to reply clear answer to you.

Thanks

Setsuda

Ok thanks a lot mr Setsuda and in also please thank your engineer mate. It's correct, the voltage across the Capacitor decreases because there is a flow of negative charge that comes from the channel of the FET onto it! I've read it also on a book found just yesterday.
Thanks a lot for your helpfulness! This community works! @ Next issue!