I am currently reading the book "The Art of Electronics 3rd Edition". However I am having some difficulties to understand chapter "3.4.1 FET analog switch". This section is about how MOSFETs can be used for switching analog signals. As an example the circuit in picture 1 is used. About this circuit it is stated, that
- "the gate signal is not at all critical, as long as it is sufficiently more positive than the largest signal (to maintain \$R_{On}\$ low)"
- "negative signals would cause the FET to turn on with the gate grounded".
However, I don't understand both statements. I would perfectly agree to them, if the body was connected to the source. But this is not the case, instead the body is connected to ground. Therefore I assume that the electric field between gate and body (which leads to inversion of the semiconductor below the gate) is only changed by \$V_{Gate}\$ and \$V_{Body}\$, but not by \$V_{Drain}\$ or \$V_{Source}\$. But if this is true, the state of the FET should not be affected by the signal voltage, which contradicts both preceding statements... I would be grateful if somebody could help me with this issue :)