Does the signal direction matter for a series N-channel FET switch circuit?
The series-connected FET is a common analog switch.
It is assumed that input DC voltage and output DC voltage are identical. Sometimes you see both drain &amp; source biased at some positive voltage (perhaps +5v) so that when the gate is grounded, the FET channel is blocked.
Other circuits have both drain &amp; source DC-grounded through resistors. To turn the FET OFF, gate voltage must be pulled to a negative voltage.
Regardless, when the gate is at the same DC potential as the channel, the FET source-to-drain resistance is fairly small - tens to hundreds of ohms.
Many FETS can have drain and source swapped.
The FET switch circuit doesn't much care unless signal amplitude is large.



simulate this circuit &ndash; Schematic created using CircuitLab