The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Design >> RF Design >> calculation of total width of MOS using finger width and multiplier
https://designers-guide.org/forum/YaBB.pl?num=1516272182

Message started by Sagar Juneja on Jan 18^th, 2018, 2:42am

Title: calculation of total width of MOS using finger width and multiplier
Post by Sagar Juneja on Jan 18^th, 2018, 2:42am

If we are given a finger width, numbers of fingers and multiplier then as per my understanding the total width of MOS = finger_width*number_of_fingers*multiplier.

Is my understanding correct? I refereed to one sample circuit in cadence manual, i am not been able to understand how they have calculated the total width. Screenshot is attached.

Title: Re: calculation of total width of MOS using finger width and multiplier
Post by Andrew Beckett on Jan 21^st, 2018, 8:26am

The example is not a particularly great one because it's inconsistent. The database is from the SpectreRF workshop which is in <SPECTREinstDir>/tools/spectre/examples/SpectreRF_workshop/rfworkshop.tar.Z and looking at the CDF for this component, it seems that most of the parameters are not used - it's only the length, the multiplier, and the number of fingers that are netlisted for these RF transistors. The width is defined in the model as 1.5u. The other parameters which are displayed in the edit properties form are not consistent - there are no callbacks to compute them.

So don't get too hung up on this specific example - it's not intended to be a real life PDK - it's an example which has been adapted a few times and is not representative of a real-life design kit.

Regards,

Andrew.

Title: Re: calculation of total width of MOS using finger width and multiplier
Post by Tako on Jan 23^rd, 2018, 5:22am

Generally speaking this formula:

total width of MOS = finger_width*number_of_fingers*multiplier

is a proper one. But keep in mind that 1um x 4 x 5 (W x F x M) transistor would behave a little differently than 2.5um x 2 x 4 transistor .