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leonken
Joined: 12 Jun 2004
Posts: 210
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 19 Oct 2004 19:06 How to design a large resistorMeg Ohm in IC chip? |
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| for examle, I need a serveral Meg Ohm resistor. If we do not consider the accurate do you have some good approaches to make it in IC chp?
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Hughes
Joined: 10 Jun 2003
Posts: 712
Helped: 84
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| 20 Oct 2004 1:40 How to design a large resistorMeg Ohm in IC chip? |
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| If you do not consider the accuracy, you may use active resistor, a mosfet biased in linear reagion.
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selvaraja
Joined: 01 Jun 2004
Posts: 220
Helped: 3
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| 21 Oct 2004 3:30 Re: How to design a large resistorMeg Ohm in IC chip? |
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Hi
can use diffusion resistor if resistor value big but accuracy is trade offf
regards
selvaraja
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sunking
Joined: 25 May 2004
Posts: 914
Helped: 46
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| 21 Oct 2004 3:39 Re: How to design a large resistorMeg Ohm in IC chip? |
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| Hi poly resistor or well resistor
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tlihu
Joined: 02 Jan 2002
Posts: 627
Helped: 5
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| 21 Oct 2004 4:14 How to design a large resistorMeg Ohm in IC chip? |
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| There is HR (High Resistance) poly, usually 1k/sq.
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IanP
Joined: 05 Oct 2004
Posts: 6346
Helped: 1505
Location: West Coast
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| 21 Oct 2004 4:22 Re: How to design a large resistorMeg Ohm in IC chip? |
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Better then MOSFET will work FET transistor as from its nature it is electrically controlled resistor. And for you it probably does not matter if it is in linear or non-linear area as long as you can achieve required resistance... 
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Hughes
Joined: 10 Jun 2003
Posts: 712
Helped: 84
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| 21 Oct 2004 13:20 Re: How to design a large resistorMeg Ohm in IC chip? |
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| Poly and diffusion resistors are process related. In mixed-signal CMOS process, poly resistors with 1kOhm/sq. sheet resistance may be available. But in submicron standard logic CMOS process with salicide, the sheet resistance of poly and diffusion may be a few ohms/sq.
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xinyin
Joined: 29 May 2002
Posts: 18
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| 21 Oct 2004 13:39 How to design a large resistorMeg Ohm in IC chip? |
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| It depends on your process. Check with you process manual to find proper resistor, or active resistors can be used.
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rambus_ddr
Joined: 26 Jun 2001
Posts: 119
Helped: 4
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| 21 Oct 2004 17:01 Re: How to design a large resistorMeg Ohm in IC chip? |
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| This resistor is too large to use a real reistor, which have large capacitor and area, i think it should be an active reistor, such as a mos transistor.
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sunking
Joined: 25 May 2004
Posts: 914
Helped: 46
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| 22 Oct 2004 5:43 Re: How to design a large resistorMeg Ohm in IC chip? |
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| An other method is R=T/C, using switch cap.
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cetc1525
Joined: 08 Oct 2004
Posts: 177
Helped: 3
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| 22 Oct 2004 12:41 Re: How to design a large resistorMeg Ohm in IC chip? |
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| "Meg Ohm" is very large in IC design.we don't suggest designers use a real resistor.did you think of using a current source ?
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extraord
Joined: 05 Mar 2004
Posts: 68
Helped: 6
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| 22 Oct 2004 14:11 Re: How to design a large resistorMeg Ohm in IC chip? |
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| current source has many limits, I don't think it what the poster really want.
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tedchen
Joined: 13 Jan 2003
Posts: 19
Helped: 1
Location: United State
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| 22 Oct 2004 20:03 Re: How to design a large resistorMeg Ohm in IC chip? |
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Usually, the N-Well got the highest resistance per square but worst accuracy so not many people wanna take that risk. The alternative would be poly resistors. According to TSMC documents, the Rsh of P- poly w/o silicide can goes up to around 1k ohms/sq while P+ poly w/o silicide is only slightly over 300 ohms/sq, for 0.18um. BTW, N+ poly w/o silicide got 200 something, nearly 300 ohms/sq.
About how to layout it out, there are couple books talking about resistor layout, capacitor layout, etc. You can probably check the book "The Art of Analog Layout" first.
About the size, if you are going to use poly resistor, I don't think the size will be too big compare to capacitors or inductors. I personally laid out couple 5x MOhms resistors but the capacitor wes the biggest area consumer.
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atmaca
Joined: 13 Jan 2004
Posts: 352
Helped: 1
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| 22 Oct 2004 23:03 Re: How to design a large resistorMeg Ohm in IC chip? |
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In my opinion the best method is to use switched capacitor circuit. R= delta t / C. As in the formula you can change the resistor value by changing switching period.
Thanks
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devrimaksin
Joined: 13 Oct 2004
Posts: 93
Helped: 9
Location: Dallas, Texas, USA
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| 23 Oct 2004 1:57 How to design a large resistorMeg Ohm in IC chip? |
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| N-well is the layer to go
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terryssw
Joined: 18 Apr 2004
Posts: 176
Helped: 14
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| 24 Oct 2004 11:11 Re: How to design a large resistorMeg Ohm in IC chip? |
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| Depends on applications, I think switched-cap ones can only used when discretized mode of resistance is required (which means we must have some clock)
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bastos4321
Joined: 01 Jan 1970
Posts: 334
Helped: 24
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| 24 Oct 2004 19:52 Re: How to design a large resistorMeg Ohm in IC chip? |
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I would recommend a switched-capacitor solution. Is the best in term of area for a Meg resistor.
Bastos
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Fom
Joined: 10 Mar 2004
Posts: 759
Helped: 56
Location: Taiwan
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| 25 Oct 2004 2:40 Re: How to design a large resistorMeg Ohm in IC chip? |
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| N-well is not the best option because pitch (min width + min space) rule too large. Usually I use the following figure of merit: min one square area divided by sheet resistivity. After that you can easily estimate resistor area. Just multiply this coefficient by resistor value.
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cetc1525
Joined: 08 Oct 2004
Posts: 177
Helped: 3
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| 26 Oct 2004 6:06 How to design a large resistorMeg Ohm in IC chip? |
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| I just want to say that this resistor must occupy a large area of the layout.so, I think your structure must has some problems.
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leonken
Joined: 12 Jun 2004
Posts: 210
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| 26 Oct 2004 8:07 Re: How to design a large resistorMeg Ohm in IC chip? |
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1.switched-capacitor need another clock circuit
2. and if I need a big resistor, the frequency should be smal. So, how to generate a large period signal ? a big resistor or capacitor maybe needed.
3. If I need several resistors in series. The switched-capacitor approach also works?
thank you!
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leonken
Joined: 12 Jun 2004
Posts: 210
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| 26 Oct 2004 8:08 Re: How to design a large resistorMeg Ohm in IC chip? |
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| active resistor, a mosfet biased in linear reagion means the diode connection of a mosfet?
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leonken
Joined: 12 Jun 2004
Posts: 210
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| 26 Oct 2004 8:15 Re: How to design a large resistorMeg Ohm in IC chip? |
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| active resistor, a mosfet biased in linear reagion means the diode connection of a mosfet?
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leo_o2
Joined: 03 Sep 2004
Posts: 337
Helped: 20
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| 26 Oct 2004 9:36 Re: How to design a large resistorMeg Ohm in IC chip? |
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For active resistor, you should not connect MOSFET as a diode-connection.
You can connect it like a switch. Just adjust VGS and VDS to make sure it work in linear region. The condition is VDS<VGS-Vth
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