how to calculate the Resistance of M1 & M2 in saturation mode ?

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Venkatlab

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how to calculate the Resistance of M1 & M2 in saturation mode ?

What is the current though M1 & M2? Ideally it would be Iref but what would be practical case?

IRFL210--MOSFET part number
 

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I guess my question was not clear.
Let me split my questions.
Assume VDD=10V.
Requirement for Iout = 10mA.
What should be R value?How to calculate it?
MOSFET PN: IRFL210
 

Saturation is the mode in the MOSFET where it is fully operational conducting (non-linear mode or amplifying mode).
Based on that, the circuit you are presenting is a double MOSFET in mirror mode (Current in M1 is approx the same current that in M2 supposing that M1 and M2 are almost identical transistors)
Simple_MOSFET_mirror.png
R is calculated based on the desired current and the output Iout, Vdd and the drop voltage of M1 (that based on your PDF is around 4V, using an Iref = 10mA
Based on that
\[R=\frac{ { V}_{DD }- { V}_{GS }}{ {I }_{REF }}\]

\[R=\frac{ 10- 4}{ 10}\cdot{ 10}^{ 3}\approx600\Omega\]

You can try yourself using some documentation. Here is one: **broken link removed**
 

Thanks pedroromanvr for the immediate response.
 

Hi,

In the datasheet, VGS min=2 & max=4V.
On What basis Vgs would vary?
on keeping the Vdd within +/-1% accuracy, R +/-1%, with varrying Vout. What is the variation expected in Vgs?
 

Hi Venkat:

No, in the datasheet the \[{V }_{ GS}\] may vary from 2V to 4V. But that is the case when \[{V }_{ GS} = {V }_{ DS}\], check always for the test conditions.


By the way, I got the information using Fig 1 and Fig 3 from the datasheet.



As you can see, for a \[{V }_{ DS}=10V\], the current you are trying to use (\[{10 }^{-2 }A\]), won't produce any given \[{V }_{ GS}\], thus your transistor can disipate much more power than the case you are giving to it.
Based on the Fig 3, the \[{V }_{ GS}\] is tending to be 4V when \[{I }_{ D}\] is very small, so I use this value for \[{V }_{ GS}\]
 

Hi All,

What is the variation expected in Current mirror due to MOSFET mismatch? what are the other parameters that can affect the accuracy?
 

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