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taofeng
Joined: 21 Mar 2006
Posts: 98
Helped: 1
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 09 Aug 2008 23:00 large R value with polysilicon resistor |
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hi,
Want to know which is a better way to implement a large value R (about 400K ohms) ? with one large size R or put a lot of small r in series ?
regards,
jeffrey
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JoannesPaulus
Joined: 19 Mar 2008
Posts: 59
Helped: 8
Location: POLAND
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| 09 Aug 2008 23:54 large R value with polysilicon resistor |
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| It depends on the accuracy you need. It you have a lot of small resistors in series, the contact resistance might become a big contributor in the total resistance.
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malizevzek
Joined: 01 Apr 2008
Posts: 82
Helped: 6
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| 11 Aug 2008 9:50 Re: large R value with polysilicon resistor |
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| If you layout only one big resistor, the absolute error will be dominated from process variability. Of course, if you have a lot of smaller resistors in series, the contact resistances come into play as well. For high poly option is the contact resistance even higher.
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rillyxue
Joined: 03 Jan 2007
Posts: 27
Helped: 1
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| 15 Aug 2008 8:33 large R value with polysilicon resistor |
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| i think , some r in series will be better, it is easy to layout.
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jecyhale
Joined: 19 Feb 2008
Posts: 447
Helped: 46
Location: China
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| 19 Aug 2008 10:51 Re: large R value with polysilicon resistor |
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| taofeng wrote: |
hi,
Want to know which is a better way to implement a large value R (about 400K ohms) ? with one large size R or put a lot of small r in series ?
regards,
jeffrey |
Ｉ ｔｈｉｎｋ ｉｔ ｉｓ ｂｅｔｔｅｒ ｔｏ ｐｕｔ ｔｈｅｍ ｉｎ ｓｅｒｉｅｓ．
Ａｎｄ ｕｓｕａｌｌｙ， ｗｅ ｌａｙｏｕｔ ｔｈｅ ｌａｒｇｅ ｖａｌｕｅ ｒｅｓｉｓｔｏｒ ｔｏ ａ ｓｑｕａｒｅ．
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electronrancher
Joined: 24 Mar 2002
Posts: 474
Helped: 34
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| 19 Aug 2008 21:39 large R value with polysilicon resistor |
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| You shouldn't use a very small resistor segment, but I expect your poly is about 2k per square. So make 20 resistors of 20k each. One example would be 40 micron length and 2 micron width if you want fairly accurate resistors. Or shrink it to the minimum width if you just want a divider and don't care about absolute value.
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ytliang
Joined: 04 Aug 2008
Posts: 61
Helped: 5
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| 20 Aug 2008 10:34 large R value with polysilicon resistor |
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| Usually, resistors are laid out with segments of smaller resistors in series. I would think this gives a more accurate result
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mdcui
Joined: 23 Aug 2005
Posts: 95
Helped: 18
Location: China shanghai
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| 26 Aug 2008 3:24 large R value with polysilicon resistor |
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poly resistors usually can not reach very big value, in our process, it is only ~20ohms/square, I am not sure what kind of process as electronrancher mentioned can achieve 2k/square poly resistance.
in our design, once we want big resistor, we use N-well resistor, not so accurate as poly resistor, but it has 1k~2kohm per square. check with your process information to see if you have that component available.
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ytliang
Joined: 04 Aug 2008
Posts: 61
Helped: 5
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| 27 Aug 2008 4:28 Re: large R value with polysilicon resistor |
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| mdcui wrote: |
poly resistors usually can not reach very big value, in our process, it is only ~20ohms/square, I am not sure what kind of process as electronrancher mentioned can achieve 2k/square poly resistance.
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There are processes with high resistance poly resistors (2k/square, 1k/square). They are non-silicided, so they have higher resistance.
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