Fingering in Circuit Design...

[bharatsmile2007]

Hi All,

what are the advantages and disadvantages of fingering a transistor in circuit design?

I have transistors M1 and M2 with widths/lengths as W1/L1 and W2/L2 respectively.If there are connected in series together as shown in the figure.what would be the value of widths/lengths (W3/L3) of M3 transistor which is equivalent to M1 and M2?

Thanks

 

[henrywent]

hi,
the equivalent width W3/L3 =1/((L1/W1)+(L2/W2))
regards,
henry

 

[calculus_cuthbert]

when the transistors are connected in series, the equivalent channel resistance is increased, so I would say that the length of M3 would be L3 = L1+L2 and the width would remain the same

 

[deepak242003]

hi bharat,
you can share both the drains. This will reduce the drain to subs capaciatce as compare to M1 and M2 .. moreover i believe that effective lenght will be L1 + L2 wiht teh width same......

 

[acidwabbit]

I agree with calculus, for transistors in series, you will add up the lengths with width remaining the same and for transistors in parallel you will add up the widths with lengths remaining the same

 

[leo_o2]

I don't recommend this kind of equivalence. In fact, it will usually lead to huge difference. Please take into consideration effective lengh and effective width. It is better to run simulation to obtain the axact value.