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How to bias Gilbert mixer

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guilinwxb

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Hi, everyone:
I am designing a conventional Gilbert mixer, I am biasing the circuit to guarantee all switch transistors operate at saturation region. Is it right?
anyone can tell me ?
Thanks a lot !
guilinwxb
 

Hi, I think the purpose of biasing the switch transistor is to switch them easily.
In other words, they will be turned on or off quickly.
So they should be biased at the saturation region.
And at the same time, you must confirm the RF input transistor operate at saturation region.
Make Vds≥Vgs.
 

Thanks jecyhale.
I found the IIP3 of the mixer is increase when the Vds of switch transistor is increase...
 

Is that because of the increase of the Gm
 

jecyhale said:
Hi, I think the purpose of biasing the switch transistor is to switch them easily.
In other words, they will be turned on or off quickly.
So they should be biased at the region between saturation and linearity region.
And at the same time, you must confirm the RF input transistor operate at saturation region.
Click to expand...

Why in saturation the switch is turned on/off faster?

And I think the switches should be biased(DC) between on and off region,not saturation and linearity region

Added after 47 seconds:

guilinwxb said:
Thanks jecyhale.
I found the IIP3 of the mixer is increase when the Vds of switch transistor is increase...
Click to expand...
what is this Vds?AC amplitude or DC?
 

fanshuo said:
jecyhale said:
Hi, I think the purpose of biasing the switch transistor is to switch them easily.
In other words, they will be turned on or off quickly.
So they should be biased at the region between saturation and linearity region.
And at the same time, you must confirm the RF input transistor operate at saturation region.
Click to expand...

Why in saturation the switch is turned on/off faster?

And I think the switches should be biased(DC) between on and off region,not saturation and linearity region

Added after 47 seconds:

guilinwxb said:
Thanks jecyhale.
I found the IIP3 of the mixer is increase when the Vds of switch transistor is increase...
Click to expand...
what is this Vds?AC amplitude or DC?
Click to expand...

Yes we should bias it between on and off region.

Added after 5 minutes:

guilinwxb said:
Thanks jecyhale.
I found the IIP3 of the mixer is increase when the Vds of switch transistor is increase...
Click to expand...

I think large Vds of switch transistor can cause large linearity.
Because for large Vds mos, the mos is always located in saturation region or turned of when the Vgs change .
I may make a mistake. When Vds≥Vgs, the linearity increase.
So, if you use all nmos structure, you should make Vg≤Vd.
 

Why Vds≥Vgs leads to better linearity?Any explanation for this.
I doubt that maybe Vds means a larger bias current which leads to better linearity.
 

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