Electrical – switch that can replace Voltage Controlled Switches

Without knowing the exact details regarding the circuit connections that the switch was connected to it is not possible to give a generic answer as to what semiconductor components could replace the switch.

What you can do though is to select a relay that has contacts with ratings similar to the switch. Ratings being the current carrying capacity of the contacts and the open circuit voltage rating of the contacts. And whether specified for AC or DC service.

With the relay in place you can now control the relay coil as suitable to your remote control system and be totally isolated from the device which is being switched.

3rd one doesn't work as XOR.

Look at case A=0, B=0:
Upper right MOSFET (p-channel) is turned ON. This yields 1 at the output which is wrong.

Also look at case A=0, B=1:
Upper left MOSFET (p-channel) is turned ON, which makes source of lower right MOSFET (n-channel) high.
Gate of lower right MOSFET (n-channel) is high but its source is also high.
N-channel MOSFET is, however, supposed to be used only as switch to low.

And to answer your question "How do you simplify a CMOS circuit?":

• be creative and check that your circuit yields correct output value in all cases (i.e. here in all 4 cases: A=0, B=0 → 0;   A=1, B=0 → 1;   A=0, B=1 → 1;   A=1, B=1 → 0).
• N-channel transistors (the ones without bubble at the gate) are turned ON by "1" at gate. Use them only as switch to "0".
  P-channel transistors (the ones with bubble at the gate) are turned ON by "0". Use them only as switch to "1".