"backategate coupling" In the chapter 6, of (Jan M. Rabaey)

[palmeiras]

Hi everyone,

In the chapter 6, of (Jan M. Rabaey), he explains the “backategate coupling”.
This effect is shown in the attached figure.
Please, could someone explain why Cout2 does not go to exact gnd – when “in” goes from zero to 1? The figure shows that it Is not possible to completely discharge capacitor CL2.

Thank you,

Regards,

 

[kalyanasv]

The circuit you have drawn is dynamic logic circuit. So the principle behind the capacitive coupling is that the voltage at CL1 starts charging CL2 even though CL2 discharges through M3 and M4. Thus, Out1 voltage drops charging Out2 which is not able to discharge to GND.

 

[palmeiras]

kalyanasv,

Thanks for your reply.
I didn’t understand you explanation, because the circuit in this situation has a direct path to ground. The terminals of any parasitic capacitance connected in this path will be set to gnd.
So again, why cout2 does not achieve gnd?

Thanks,

 

[kalyanasv]

Here out2 gets charged by out1 [capacitor connection between M4 Gate-drain]. Thereby though CL2 at out2 would discharge it won't be able to completely.