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30th April 2004, 03:17 #1
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gate resistance
Can anybody show me how to calculate the gate resistance(Rg) in a MOSFET? It's better to give some example on calculation or simulation on that matter!
From 'Impact of Distributed Gate Resistance on The Performance of MOS Devices' by B.Razavi, R.Hong Yan and Kwing F.Lee it shows that there is a relation between Rg/3 and 1/gm.
8O

30th April 2004, 03:43 #2
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mosfet gate resistance
Mabey you can try small signal circuit calculation.
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30th April 2004, 03:43

30th April 2004, 05:45 #3
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gate resistance mosfet
I think you also need consider gate capcitor,gate resistor is relate about gate capcitor!
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30th April 2004, 05:52 #4
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fet gate resistance
you also reference this application:
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30th April 2004, 05:52

30th April 2004, 08:07 #5
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mosfet gate resistor calculation
gate resistance refers to the resistance of the gate material, that combined with the gate capacitance give a distributed trnasimision line. This affects the transistor frequency response. Calculate gate resistance as a sinple poly stripe. Gate resistance depends on if you connect the gate from only one side, or is you do it from both sides.

30th April 2004, 09:33 #6
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gate resistor mosfet
Look at datasheet of MOSFET transistor you plat to use, they reccomed gate resistor.
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30th April 2004, 09:33

30th April 2004, 10:11 #7
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calculating mosfet gate resistance
Actually, why I'm asking all of you about gate resistance is due to calculate the input impedance of my LNA design! :D
As you can see in the attachment, the circuit and the input impedance equation are as depicted!
R1 = is the Lg and Ls paracitic resistance
Rg = is the effective gate resistance
= R0*W/3*n*n*L
 R0=sheet resistance (as RSH in SPICE parameter)
 n = number of fingers
Therefore, to get Zin=50, I have to include Rg and R1 to my calculation.
Is the Rg equation can be used??

30th April 2004, 12:25 #8
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gate resistance calculation
Hello,
As previously mentioned, you need to know the layout used when creating the gate process. I'm not sure why there's an n squared in the denominator; I was only expecting n. You hab=ve the factor of 3 in the denominator to account for the distributed nature of the gate transmission properties if it's a single ended connection, however a factor of 12 is required if it is doubly connected. If you look at some of the BSIM3 manuals, the Zin is discussed at great length and some finer corrections are included to improve the accuracy.
Regards,
MoonShine

30th April 2004, 16:53 #9
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calculating gate resistance
for an experimental circuit, I guess you could use gate resistance to get Zin=50Ohm but I would suggest a real impedance matching front end next time. Zin depends on more than just Rgate..
But anyway, you can calculate gate resistance just by calculating the number of squares of gate material * Rshgate..
So for example, 1um long gate *100um wide * 50mOhm per square gives you 5 ohms per gate finger. Five gates in parallel gives you 1Ohm.
Now that I think about it, if you make a 50Ohm gate it will be so wide you will get travelling waves  the contact side will turn on way before the other end. Could you try some sort of commonbase impedance matching circuit? Or actually draw a 50Ohm resistor to take the input across (will also vary 20%) but then you can build a lower Rgate (and therefore much faster) input pair. Just my opinion, though.. Good Luck!

30th April 2004, 19:55 #10
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calculate gate resistor
Thomas LEE has a very good paper about Rg effect on LNA design in JSSC. You can check that.
IEEE JOURNAL OF SOLIDSTATE CIRCUITS, VOL. 32, NO. 5, MAY 1997
"A 1.5V, 1.5GHz CMOS Low Noise Amplifier"

30th April 2004, 19:55

1st May 2004, 03:42 #11
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mosfet rg
I'm using inductive source degenerated as my input matching(depicted in my previous post), so...Rg is not my only point a matching component.
By electronrancher:
"So for example, 1um long gate *100um wide * 50mOhm per square gives you 5 ohms per gate finger. Five gates in parallel gives you 1Ohm.
Con you explain in detail on that matter because I'm a new in using fingers in my design & layout. How can in 5 parallel with 5 ohms per gate finger we can get 10ohm??
Very courious...

1st May 2004, 07:05 #12
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mos gate finger and gate capacitance
that's just ohm's law for parallel resistors. 55555 = 1

29th December 2009, 07:20 #13
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About MOSFET gate resistance!!
great.
so many sages.
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