# how to get rid of pole while keep zero ?

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#### lxcpku

##### Junior Member level 3
Hi,all
in some application,to ensure the stability,i like to get rid of pole while keep zero . but i donot know how to achieve that. anyone could tell me ?

another question:
how to acquire the zero expression without deducing transfer function.

thx a lot

#### maninnet

##### Member level 5
i don't think there will be a general answer to you 1st question; for the 2nd question, i don't know if there is some general method to find the zero(roughly) by inspection, but in some cases, it could, refer to razavi's design of analog cmos ic, page 176, the last paragraph, then you will get the idea.

#### electronics_kumar

////how to acquire the zero expression without deducing transfer function. ////

I AM ALSO in need answer for that ..all i know is i can derive equation for pole and zero from the knowledge of TRansfer function....
help US thro ur explainations..............

#### lxcpku

##### Junior Member level 3
maninnet said:
i don't think there will be a general answer to you 1st question; for the 2nd question, i don't know if there is some general method to find the zero(roughly) by inspection, but in some cases, it could, refer to razavi's design of analog cmos ic, page 176, the last paragraph, then you will get the idea.

thx u for ur help
and also i got another way to evaluate zero, that is ,as we know,there is two branches from input to output, when the current through two branches is equal,then we can acquire zero

#### maninnet

##### Member level 5
there is two branches from input to output, when the current through two branches is equal,then we can acquire zero

the two currents are equal, but their direction need to be opposite