gm/Id methodology for biasing transistor

I am designing a Fully diff Folded cascode OTA and for this I need to design a wide swing bias.
I read a lot about gm/Id methodology used to bias transistors in strong inversion for having a good design.
But I could not get get proper rersourse to follow this method. Dose anybody have resources related to gm/Id methodology?

Any help will be welcommed.
Thanks in advance.

Cheers

predator89 said:

... gm/Id methodology used to bias transistors in strong inversion

Click to expand...

It is correct to use bias transistors in strong inversion, but for strong inversion operation the gm/Id methodology isn't the correct design method: the gm/Id methodology is used for moderate or weak inversion operation.

Use standard, i.e. strong inversion operation design methods for bias transistors: Use long transistors (L ≧ 10*Lmin) for high output resistance and low supply voltage dependency, and choose the width W for strong inversion operation for the required current and bias voltage.

Depending on technology size and required current you often end up with W/L < 1 for low bias current.

predator89 said:

I am designing a Fully diff Folded cascode OTA and for this I need to design a wide swing bias.
I read a lot about gm/Id methodology used to bias transistors in strong inversion for having a good design.
But I could not get get proper rersourse to follow this method. Dose anybody have resources related to gm/Id methodology?

Any help will be welcommed.
Thanks in advance.


Cheers

Click to expand...

Boris murman has given beautiful notes to understand Gm/Id method. See below in chapter-5, gm/Id based design
**broken link removed**





"Take a step forward and things will start happening automatically"
~Rahul

Rahul Sharma said:

Boris murman has given beautiful notes to understand Gm/Id method. See below in chapter-5, gm/Id based design
**broken link removed**

Click to expand...

Thanks!! These are very nice notes for gm/Id method.

But I am stuck at plotting graph for gm/id in Cadence spectre. I am not able to understand how to plot gm during DC sweep. Please guide me with this.

predator89 said:

Thanks!! These are very nice notes for gm/Id method.

But I am stuck at plotting graph for gm/id in Cadence spectre. I am not able to understand how to plot gm during DC sweep. Please guide me with this.

Click to expand...

Hi

See if you are taking to plot the gm/Id graph with respect to Vgs sweep then it is quit obvious to plot using calculator functions.
-First, you will plot Id Vs Vgs (u will get one plot say plot-1)
-Second, Differentiate Id with respect to Vgs using calculator (u will get another plot, say plot-2)
-third, divide plot-2 with plot-1 using calculator and the final result will be nothing but gm/Id Vs Vgs

ps- This may be the solution if i understood your question right.


-Rahul

Rahul Sharma said:

See if you are taking to plot the gm/Id graph with respect to Vgs sweep then it is quit obvious to plot using calculator functions.
-First, you will plot Id Vs Vgs (u will get one plot say plot-1)
-Second, Differentiate Id with respect to Vgs using calculator (u will get another plot, say plot-2)
-third, divide plot-2 with plot-1 using calculator and the final result will be nothing but gm/Id Vs Vgs

-Rahul

Click to expand...

Yes this was my question. I am new to cadence and not used the calculator functions much. I will try this out.

Thanks a lot!!