finger and multiplier

[ee171]

finger multiplier

Hi all,
sorry for a dumb question.. but what is the different between a finger and a multiplier? it would be great if you have a snapshot of a layout. thanks

 

[varma_cs012]

multiplier finger nmos

Please go through the below topic. If u still have questions u can post reply.
U will definetly get answer. Thank you.

 

[siddharthshukla]

nmos finger multiplier

fingers are made when a mos havinga alarge w/l is split up into smaller Moses of lesser w/l's in parallel.the equivalent w/l and hence gm of the combination remains the same but using fingers dramatically reduces the parsitics aasociated withe the junctions as well as gives the layout a better aspect ratio

 

[sridhar540]

HELLO SIDHARTHSHUKLA

I AGREE WITH U

BUT THE WIDTH IS REDUCED IN THE FINGERING CONCEPT BUT NOT LENGTH.LENGTH REMAINS CONSTANT.

 

[siddharthshukla]

ya sridhar i agree what i meant was becoz of width reducing it reduces the w/l of the finger transistors further in layout if the difference in size of W & L is not too high it gives rise to symmetric and nice layout with a good aspect ratio.

 

[yaasi]

Let us consider we have one transitor with Width(w)=5u, Length(l)=2u, Fingers(f)=3, Multiplier(m)=4.
That means you have 4 transistors each with 3 fingers and with w=5u, l=2u for each finger.

If a transistor has 3 fingers then it means that its either S or D are merged and we should connect the rest(S/D) .


The total width of transistor =w * f * m (w-width,f-fingers,m-multipliers)....

Added after 56 seconds:

Let us consider we have one transitor with Width(w)=5u, Length(l)=2u, Fingers(f)=3, Multiplier(m)=4.
That means you have 4 transistors each with 3 fingers and with w=5u, l=2u for each finger.

If a transistor has 3 fingers then it means that its either S or D are merged and we should connect the rest(S/D) .


The total width of transistor =w * f * m (w-width,f-fingers,m-multipliers)....

 

[spring1860]

some body said it is better to set even number of fingers ,but i dont know why .can some one explain ?

 

[salma ali bakr]

the fingers and multipliers are the same for the LVS tool
they're translated into multipliers at the end in the CDL file...
choosing fingers and multipliers is the designer's task
but regarding the final width...it's just the transistor width multiplied by the fingers and the multipliers...that's all

 

[sridhar540]

Becuause even fingers are easy to match, easy to form good common centroid and interdization patterns than the odd fingers.

 

[jecyhale]

For matching, and if the MOS is too large, we will divide one MOS to double, so we will use the multiplier.