Hello ,I have a regulator for 5V which are biasing several amplifier in parralel with 600mA in total.
I also have several RFSA2113 variable attenuators I need to controll.
Each variable attenuator device needs 3V vdd and 0 to 2V as Vc.

So I just took the 5V which I biased ,connected it to a buffer to isolate the stage.
then from 5V I made 3V using TL431.
Then I made several resistor dividors to have 0V-2V and I just put the 3V ad VDD to all of them.
Is it a good method to bias these several variable attenuators.
photo of the schematics Ltspice simulation and RFSA2113 is attached.

 

So I just took the 5V which I biased ,connected it to a buffer to isolate the stage.
then from 5V I made 3V using TL431.
Then I made several resistor dividors to have 0V-2V and I just put the 3V ad VDD to all of them.

hi yef,
This LTSpice plot shows the VC as being well outside the specified 0V to 2.5V ? [Tempr 0C thru 100C]
How do you plan to vary the VC voltage?
Also, if all 4 Attn's have the same VC voltage applied, why not link all 4 VC inputs together and use an OPA with a low output impedance to drive the VC voltage range?
E

 

Hello Eric,instead of a resistor I will put a trimmer to change induvidualy vary the value of Vc.
I made the resistor much smaller as shown sbelow so they fit the range of Vc
Do you see any logical problem in the method of biasing the attenuators in such way?
to use TL431 and a opamp buffer in such way ?

 

hi yef,
Try this alternative circuit, drive all the VC attn input linked together.
E

 

Hello Eric I have 4 variable attenuators each one needs Vdd=3V and individual Vc.
Vc1 Vc2 Vc3 Vc4.
So you reccomend to use single TL431 for all variable attenuators and have aunique buffer+resistor divider for each variable attenuator?
If its what you reccomend what is the physical intuition behind it?
Thanks.

 

Hi yef,
I consider the low output impedance of the OPA driver being a better choice than using the TL431 direct.
I would join all the VC attn together, in that way all the Attn will get the same control voltage.
E

 

Hello Eric , but if I give them the same control voltage then I could not control each one individually.