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What happens when the width is too large for the length of the MOSFET?

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littlerock

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Let's say that I have a PMOS with w=25um and length is l=0.1um m =1. What is the effect if I will change this size to w=5um and l=0.1um m=5. Is there a negative effect when the width is too large for the length of the MOSFET? How about on the layout of the MOSFET, which is better between the two?

Thanks for your help. :)
 

25um width is not too large for a 100nm long device I think, you could use that if it fit better next to other blocks. If the width is much longer there are DFM rules which assert, I don't know them. But I know that if you connect at the endpoint of the gate the poly will have got higher series resistance for a wider device, and it decreases the bandwidth of the device and increase gate resistance caused thermal noise.
 

frankrose said:
25um width is not too large for a 100nm long device I think, you could use that if it fit better next to other blocks.
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Thanks, frankrose! I will be using this transistor size for my tapered buffer. The w=25u, l=0.1u will be for the PMOS and then the NMOS will be w=10um, l=0.1u. I will be driving a large device with this buffer and the multiplier with that size of the transistors for the last stage of the buffer will reach about 30000. Is that fine?
 

I don't know your load and timing requirements so I cannot say it is fine. 30000 sounds too big, probably your inverter or buffer will need a pre-amp or buffer too.
 

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