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phutanesv
Joined: 26 Apr 2007
Posts: 150
Helped: 12
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 09 May 2007 11:44 why nand gates are faster than nor |
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Dear friends,
why do NAND gates are more preferred than NOR gates
One reason is NAND has series NMOS and Parallel.
But what is the reason behind this. If Nmos in series what is benifit
Excat explanation i need.
Pls do
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drizzle
Joined: 07 Jun 2006
Posts: 56
Helped: 2
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09 May 2007 12:18 Why Nand is more preferred than NOR |
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the sum of internal capacitance of Nmos in series is less than that of in parallel, so VDD have a more faster charge rate for Nand.
we can instead of Nor by four nands.in my opinion, nand is more fundation than nor.
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sameer_dlh25
Joined: 21 Sep 2005
Posts: 85
Helped: 13
Location: Bangalore India
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09 May 2007 12:32 Re: Why Nand is more preferred than NOR |
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As far as I know in case of
1. PMOS device has less mobility. In case of NAND PMOS are in parallel and they try to compensate the mobility factor during charging. where as NMOS has more mobility and series resistance compensate for discharging time. In other words charging and discharging are balance in this case.
2. In case of NOR this is not the case and discharging of output cap is very good ( More e mobility + parallel NMOS) but charging is slow so we have bad rise time.
I hope I am clear enough 
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deh_fuhrer
Joined: 25 Jul 2006
Posts: 421
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09 May 2007 12:40 Re: Why Nand is more preferred than NOR |
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It is basically related to the gate sizing.Lets say you have a library with basic inverter size would be 2:1(Wp/Wn).To make this condition true for NAND gate you have to use two Wp pmos in pull up device and two Wn nmos in NMOS device.
In NOR gate you have to use two PMOS devices of width 4Wp as pullup device with two Wn NMOS. So you have more utilization in NOR gate.
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manenef
Joined: 09 Nov 2005
Posts: 60
Helped: 3
Location: kenya
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09 May 2007 14:19 Re: Why Nand is more preferred than NOR |
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In the design and implementation of a logic circuit, its becomes easier if the parameters are in SOP(sum of products form) other than POS(product of sum form).
NAND gate implementation of the SOP is straightforward, but POS implementation using NOR gate is abit involving, and offcourse many designers will go for the NAND gate to implememt thre circuits since its easier hence superior!
kind regards
manenef
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sekapr
Joined: 27 Jul 2006
Posts: 100
Helped: 5
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09 May 2007 21:47 Re: Why Nand is more preferred than NOR |
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| In FF based design mostly data is sampled at the rising edge of the clock. so 0->1 transition should be faster. since in nand pmos xtrs are in parallel, 0->1 transition will be faster due to lower effective resistance.
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09 May 2007 21:47 Ads |
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p_shinde
Joined: 25 Feb 2006
Posts: 299
Helped: 4
Location: tokyo
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10 May 2007 2:14 Re: Why Nand is more preferred than NOR |
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imagine connecting pmos in series.......becos of its allmost double width than nmos ....and less mobility .........it will take much time for output to change to 1,
also PMOS is better in sending logic 1 than logic 0, whereas NMOS better in sending logic 0........
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shiv_emf
Joined: 31 Aug 2005
Posts: 641
Helped: 16
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17 May 2007 16:58 Why Nand is more preferred than NOR |
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fantastic discussion here...
NAND is faster than NOR.. as explained by Sinde
shiv
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AlexWan
Joined: 26 Dec 2003
Posts: 305
Helped: 6
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18 May 2007 7:25 Why Nand is more preferred than NOR |
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For read operation, NOR is faster than NAND, a bit.
For write operation, NAND is faster than NOR, many.
If do erasure, NAND is about 4ms, while NOR is about 5s.
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rakesh1234
Joined: 12 Dec 2006
Posts: 95
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18 May 2007 10:56 Re: Why Nand is more preferred than NOR |
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excellent discussion
The ultimate result is nand is faster than nor
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