Resistors' values of a Current Reference for LNA??? (Thomas H.Lee's example)

[jianke]

Hi everyone! I am learning to design a CMOS LNA using Thomas H.Lee's book (The Design of CMOS Radio-Frequency Integrated Circuits). But I am not sure about how to choose the resistors' values of a "Current Reference" (Page 386)??? The values of the two resistors are 1kohm and 2kohm.

The bias current is 5mA in his example. But, if it is changed to 6mA or another value, then how to correspondingly change the values of the resistors of the "Current Reference".

I read some books about current mirror and current reference. But the Current Reference used in Thomas H.Lee's example seems not a general structure explained in these books. Looking foward to your answer. Thanks!

 

[jianke]

Doesn't anyone have an idea or any comments?

 

[BradtheRad]

The schematic appears to use mosfets as the active components. I'm not sure why the units are micrometers (which is a physical parameter, not an electronic specification). Is there a current path through the inductor at M1? My knowledge is incomplete of course .

Anyway, as to what value to use for a current reference resistor...

It is not necessarily an automatic choice. It must be determined through experimentation. There are many variables which must be factored into the equation.

Example... The resistor network that produces 5mA reference in the schematic, may end up producing 5.5mA in real life if one resistor is 10 percent off. (This may or may not be a problem in this particular application.)

Or the reference network may produce 6mA if you raise the supply voltage by 20 percent.

With real components, if it is important to have a particular value as a current reference, then it will require direct checking of values, and adjusting to suit the requirements. At least until experience shows you what will work, and what won't work, without a need to check.