Question about cutoff frequency.

[pekoe]

What's the cutoff freq. for TSMC0.18um & TSMC0.35um technologies?

 

[andy1]

I am new to this terminology.

What is the definition of cutt-off frequency of a process?

 

[fletcher]

As I know you can obtain this frequency by simulating a simple amplifier (a folded cascode amplifier can achieve the maximum frequency or bandwidth of process)

 

[andy1]

How do you quantify the cutt-off frequency? At 3db point on the output vs. the input?

 

[pekoe]

How do you quantify the cutt-off frequency? At 3db point on the output vs. the input?

I was asked this question by someone. So I had the same doubts as you too, while I found a paper which defines the cut-off freq. as 2*pi*gm/C. C includes intrinsic input capacitance, parasitic gate-bulk capacitance, and the gate-source and gate-drain overlap capacitances. I want to know the values.

 

[flatulent]

the gm/C is adevice figure of merit from the days of valves/tubes. It is also called the 'gain bandwidth product'. It is only useful on devices with very little resistance from the controlling node (gate, base, grid) to the active part of the device. This is why it is not used for bipolar junction transistors.

 

[markty]

I think you can do a frequency domain simulation with a minimum size mosfet to get those values.

for example, you can build a single mosfet amplifier to run the simulation.

 

[andy1]

I think you can do a frequency domain simulation with a minimum size mosfet to get those values.

for example, you can build a single mosfet amplifier to run the simulation.

So I guess you plot the frequency response of output vs. input which will probably give you a low pass characteristic.

So the 3db point on the output determines the bandwidth of the amp? Where would you take the output?

 

[chinito]

If nothing specific is given to you then you can assume that 2*pi*gm/C = ft where ft is the transition frequency of your device (where the gain of the device in question is unity). The gross appx of C ~ Cgs (back of the envelope sort of thing). I hope it helps.

 

[pekoe]

Thanks for everyone's help! I think I found the answers from the paper. You can take a look if you are interested in this topic.


RF-CMOS performance trends
Woerlee, P.H.; Knitel, M.J.; van Langevelde, R.; Klaassen, D.B.M.; Tiemeijer, L.F.; Scholten, A.J.; Zegers-van Duijnhoven, A.T.A.;
Electron Devices, IEEE Transactions on , Volume: 48 , Issue: 8 , Aug. 2001
Pages:1776 - 1782

 

[serdes]

You can get these data from foundry.

 

[lakeoffire]

I think the ft is just an approximate value. It will change with the process variation or bias conditions. So 2*pi*gm/Cgs is a good approximation. Gray & Meyer's book talks about this.