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in order to eliminate body effect one way is to connect the substrate to source when the well is for a single device (PMOS with a well in a CMOS for example) , but i read that it increases the source to substrate capacitance to connect them together , i don't really know the reason why would that increase the capacitance Csb ? Thanks

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  • \$\begingroup\$ How can there be a capacitance from substrate to source if they are connected together? \$\endgroup\$ Feb 21, 2021 at 2:43
  • \$\begingroup\$ If you mean temporarily connecting them with another switch like a MOSFET, an open MOSFET has its own capacitance that would be added in parallel. \$\endgroup\$
    – K H
    Feb 21, 2021 at 8:05
  • \$\begingroup\$ @ElliotAlderson That's what i'm exactly wondering about since yesterday what are the disadvantages of eliminating body effect by connecting source and substrate together , the only one i found is the mentioned capacitance increase but i couldn't find logical reasons \$\endgroup\$ Feb 21, 2021 at 13:22

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Connecting the substrate to the source in order to eliminate the body effect in a MOSFET does increase the source-to-substrate capacitance (Csb), and the reason lies in the increased area of the capacitance plates.

The source-to-substrate capacitance is essentially the capacitance between the source and the substrate, and when the substrate is connected to the source, they effectively become part of the same conductor. The capacitance is a measure of the ability to store charge, and it depends on the surface area of the conducting plates and the separation between them.

By connecting the substrate to the source, you are increasing the effective area of the source electrode, and therefore, the capacitance between the source and substrate increases. This increase in capacitance can have implications on the overall performance of the MOSFET and may affect the circuit characteristics.

It's a trade-off between mitigating the body effect and dealing with the increased capacitance. In some cases, the increase in Csb might be negligible compared to the benefits gained by eliminating the body effect. Engineers need to carefully consider these trade-offs based on the specific requirements of their circuit design.

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