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# How to measure the ON resistance of an Analog Switch?

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#### rajblr

##### Junior Member level 3
hi every one,
can any body tell me how to measure the ON resistance of an Analog Switch. Is it Vout/Iout or anything else.

cheers
raags

Re: Analog Switch

You can estimate ON resistance of Analog Switch by Vout/Iout, but it depends on the structure of Analog Switch.

For example, if Analog Switch is composed of Transmission Gate, the ON resistance is :
[Vds(pmos)/Ids(pmos)]//[Vds(nmos)/Ids(nmos)] , or
Vab/Iab, where Vab is the ON Voltage of TG, Iab is the ON current of TG.

Re: Analog Switch

hi,
The switch comprises of two TG , an inverter for control and a pulldown transistor. The setup provided to us is, a bias voltage connected to input pin, input voltage source which need to be varied. So is that we should measure current at out and vout at outpin to calculate RON.

cheers
raags

Re: Analog Switch

You can't calculate Ron only by Vout/Iout,
but you can calculate Ron by (Vin-Vout)/Iout,
you can simulate by HSPICE, and you should find the difference.

gominman

### gominman

Points: 2
Re: Analog Switch

hi i am uploading the setup of on resistnace measurement, in which Vbias=xuvolts and vin is swept between 0 to VDD, So can you tell me how to measure Ron in this case.

cheers
raags

Analog Switch

put a amperometer in serie.
the ron is different if vin>vout or vout>vin, and decreas if cmos analog switch is alimentated from 15v instead 5v. make experience doing tests measurements

Analog Switch

the on resistance of an Analog Switch can be calculated easily according the formula in linear region of MOSFET

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