Question about analog switch

[Manchested]

Hi,

When an analog switch is in series with a current source,
will the source become saturated when the switch is open? if so, what is the best way to overcome this:?:

 

[keith1200rs]

Yes, the current source will saturate. The best way to prevent it (assuming it matters) is to provide somewhere for the current to go e.g. using a second analogue switch.

Keith

 

[Manchested]

1. If the switch is in parallel with the source, will all the current goes to the ground?
2. Will current decrease when it is passing through the switch(in series), as there's Ron resistance in the switch?
3. When the switch is closed, can i model the switch with a Resistor with a Ron resistance said in it's datasheet?

Thank you

 

[keith1200rs]

It depends on whether the current source is a sink or source. Assuming it is a source ie from VDD then the current dump switch would be to ground.

The current out will not be affected by the switch resistance. It will be affected by leakage.

Model the switch with resistance and capacitance if no proper model is available but that won't should up switching transients and charge injection .

Keith

 

[FvM]

You can also use a clamp diode instead of a second switch to provide a current path when the switch is open.

 

[JoannesPaulus]

You could also switch off the gate (disconnect the gate from the bias line with one switch in series and ground it for nmos or connect it to power for pmos).