The Designer's Guide Community Forum https://designers-guide.org/forum/YaBB.pl Design >> Analog Design >> regarding W/L ratio of transistor https://designers-guide.org/forum/YaBB.pl?num=1543486378 Message started by srinivasan0901 on Nov 29th, 2018, 2:12am

 Title: regarding W/L ratio of transistor Post by srinivasan0901 on Nov 29th, 2018, 2:12am In analog IC design , is it correct to make W/L ratio as 1. or L must always be less than W?

 Title: Re: regarding W/L ratio of transistor Post by DanielLam on Nov 29th, 2018, 12:25pm In general, the W/L ratio tends to be greater than 1. I do not know of any cases where you may want it equal or less. In my experience, you can't even do that. The minimum width is usually a little longer than the minimum length.There are cases when you do not want minimum L maybe due to mismatch or for flicker noise reduction. But in those cases, the W/L ratio is still greater than 1.**Edited to make statements correct.

 Title: Re: regarding W/L ratio of transistor Post by srinivasan0901 on Nov 29th, 2018, 2:24pm But in my class , i have designed diff amplifier, where width is several times more than length,which makes w/L >1. my doubt was for current measuring based circuits, usually L is more and almost similar to W or can be more than w. Is that way of proceeding design is correct or not?

 Title: Re: regarding W/L ratio of transistor Post by DanielLam on Nov 29th, 2018, 3:20pm Whoops, you're right. I was thinking one thing and wrote the other. I corrected my statements above.

 Title: Re: regarding W/L ratio of transistor Post by polyam on Dec 1st, 2018, 7:51am It depends on the design and the circuit you are working on, the length can be chosen more than W. I've seen a lot of circuits where the L was more than the width of the transistor especially when the device operates in weak-inversion.

 Title: Re: regarding W/L ratio of transistor Post by Tako on Mar 28th, 2019, 6:10am Sorry for late reply.In general CMOS analog IC design (comparators, opamps single-to-hundreds MHz bandwidth, bandgaps etc.), generally W/L > 1 or even W/L >> 1. For example, a single transistor may be 10/2 um in 0.18 um technology.Minimum and maximum dimensions depends on the technology, but generally Wmin is slightly larger than Lmin, e.g. 0.22/0.18 um.You may choose W/L < 1 or even W/L << 1, especially in transistor which works as resistor (current source reference, RC filter), e.g.: 0.5 / 10 um.