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rose_song
Joined: 25 Feb 2004
Posts: 15
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 26 Feb 2004 2:47 How to determine transistor size of folded cascode ota? |
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How to determine transistor size of folded cascode ota(gain=80db,fu=30Mhz)?
Thanks!
Rose
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tlbb
Joined: 13 Feb 2004
Posts: 9
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26 Feb 2004 9:23 Re: How to determine transistor size of folded cascode ota? |
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For a cascode, the gain is approximately
= gm*ro^2 = gm * (1/(Lemda*Id))^ So if you keep the bias Id unchanged while increase the width you can boost your gain. However, large transistor increase the node capacitance hence limit the bandwidth. Run the simulation to dertermin the trade off.
Be aware not to simply increase the bias Id as gm=sqrt(2*Id*Beta), increase Id will LOWER your gain!
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rose_song
Joined: 25 Feb 2004
Posts: 15
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27 Feb 2004 3:52 Re: How to determine transistor size of folded cascode ota? |
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hi,
If the ID and gm are fixed, how to determine transistor size and bias voltage of cascade output stage.
thanks!
Rose
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rambus_ddr
Joined: 26 Jun 2001
Posts: 116
Helped: 4
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27 Feb 2004 11:42 Re: How to determine transistor size of folded cascode ota? |
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| If the bias current is constant, then the swing range will be ratio to w/l, the max output voltage= vdd - 2*Vds, the min output voltage=2*Vds
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opamp741
Joined: 17 Jun 2004
Posts: 145
Helped: 10
Location: India
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17 Jun 2004 15:02 Re: How to determine transistor size of folded cascode ota? |
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1. if gm and Id are known then u can compute W/L for ur process using following eqn
gm=(2BId)^0.5
where B=Beta=Un Cox W/L
2. If u know swings pecs in ur design u can decide supplies, although it depends on ur technology. u cant choose arbitrary value
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17 Jun 2004 15:02 Ads |
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leebluer
Joined: 20 Apr 2004
Posts: 60
Helped: 2
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21 Jun 2004 3:57 Re: How to determine transistor size of folded cascode ota? |
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| "Design of analog cmos integrated circuits" by Razavi has a good example to determine transistor size of folded cascode ota, perhaps it can give u some guide.
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