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triquent
Joined: 13 Oct 2004
Posts: 166
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 09 Jan 2005 2:06 resistor value in the IC design. |
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| When we design the analog circuit, what is the maximum and minimum resistor we can design usually? how about some Mohm is OK?
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markty
Joined: 15 Dec 2004
Posts: 60
Helped: 2
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| 09 Jan 2005 3:07 resistor value in the IC design. |
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| By Mohm, u mean megaohm? That will cost a lot of area. But it is doable.
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srivatsan
Joined: 04 Aug 2004
Posts: 183
Helped: 4
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| 09 Jan 2005 4:00 Re: resistor value in the IC design. |
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Depends upon the process. Many of the values are not precise but matching is possible. MΩ may be possible, but may not be a good idea because I think that power dissipation across it may be little bit in high end for IC.
- vats
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jiangwp
Joined: 27 Jul 2004
Posts: 184
Helped: 9
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| 09 Jan 2005 14:33 Re: resistor value in the IC design. |
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The maximum and minimum is not determined for all process.
Generally , the selection of value range of resistor is determined by the accuracy , feature of temperature , feature of voltage and the requirement of performance of system. So we trade off the value of resistor and requirement of circuit.
The Mega order resistor is made by the WELL resistor. But the WELL resistor feature is poor. These parameters is referenced the PCM parameter of process.
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rongli
Joined: 13 Dec 2004
Posts: 35
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| 12 Jan 2005 13:35 resistor value in the IC design. |
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| I think Mohm is not a good way.it cost large area,not accurate.the match of resistors is good ,but the accurate is too bad.
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wee_liang
Joined: 04 Jan 2005
Posts: 26
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| 12 Jan 2005 17:10 Re: resistor value in the IC design. |
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Practically speaking, when the internal resistor reaches more than 100k, it's good to revisit the topology of the circuit, or consider external components.
Unless you're in the academic area, I guess it's ok.
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konqueror
Joined: 27 Nov 2004
Posts: 93
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| 12 Jan 2005 17:30 resistor value in the IC design. |
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usually memories (4t sram cells) require Megaohm resistors. In analog circuits it is not advisable because it will require large area which is very costly
but in case u require large resistances poly(layer2) resistances are used and they require costly processes(trimming and implant).
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yeewong_su
Joined: 12 Oct 2004
Posts: 126
Helped: 3
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| 13 Jan 2005 1:31 resistor value in the IC design. |
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| No good ideal to creative the Megaohm resistior. But it can be made
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chihyang wang
Joined: 21 Dec 2004
Posts: 8
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| 13 Jan 2005 2:15 Re: resistor value in the IC design. |
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I think Mohem may me ok if you do not need the value very precisely.
Generally speaking, you can use MOS as a resistior. You can look for TIA's AGC design for reference.
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alanbrooke
Joined: 13 Feb 2004
Posts: 40
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| 13 Jan 2005 3:07 Re: resistor value in the IC design. |
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It can, But it's not a good idea to intergrate a MEG ohm resistor inside the chip.
You can use a very narrow W, very long L NMOS and PMOS pair to do the job.
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layes2
Joined: 03 Dec 2004
Posts: 346
Helped: 5
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| 14 Jan 2005 10:16 Re: resistor value in the IC design. |
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as much as you can image but the prasitic capacitance.
so you cannot bigger than 10M i think
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andy2049
Joined: 26 May 2004
Posts: 32
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| 19 Jan 2005 3:37 Re: resistor value in the IC design. |
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The value of resistor is based on your affordable area.
Diffused resistor: 10-100 ohms/sq
Ion Implanted resistor: 0.5-2K ohms/sq
Poly Resistor: 30-200 ohms/sq
n-well resistor: 1-10k ohms/sq
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andy2000a
Joined: 18 Jul 2001
Posts: 756
Helped: 7
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| 19 Jan 2005 3:43 Re: resistor value in the IC design. |
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for cmos design like RTC circuit need ultra low current for chip ..
use n_well and use "small width" --> I think you only need large
resistor value , not need very accuracy , you can use min width for N-well
res ..
another Hi resistor use mos resistor like XTAL invert shunt Mega Ohms
for gain stage .. usually use mos switch act as Hi value resistor
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j2005
Joined: 17 Jan 2005
Posts: 44
Helped: 5
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| 19 Jan 2005 4:07 Re: resistor value in the IC design. |
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| Mohm resistors are very very rare in most designs. I'm not sure why you want such a big resistor but you obviously have to weigh the other trade offs for having such a big resistor besides the area. My guess is that you want ultra low power. At the end of the day, you can't have everything in a good analog design.
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konqueror
Joined: 27 Nov 2004
Posts: 93
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| 19 Jan 2005 5:39 resistor value in the IC design. |
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| I guess if you require Mohm resistors then you can use switch capacitor implementation which takes lesser area but it is limited to mixed signal ic's
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