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# Help needed for integrator design

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#### muiyuen

##### Junior Member level 3
In my integrator design for a ramp output, i need a large resistance value of >500kΩ. Is there anyway to realize this large resistance instead of using a resistor, since resistors take up large die area? Can i use a MOS active load? Kindly advice...thanks!

muiyuen said:
In my integrator design for a ramp output, i need a large resistance value of >500kΩ. Is there anyway to realize this large resistance instead of using a resistor, since resistors take up large die area? Can i use a MOS active load? Kindly advice...thanks!

Hi, muiyuen
Why not realize this resistor in external?
You can use the following formula to calculate the Ron
Ron=L/[KW(Vgs-Vt-Vds)] and then compare this value with the passive resistor to determin which should be used.
By the way, sometimes put some components outside of the chip is also a good choice.

sixth

u need to study hard,, its only a basic concept of designing an IC,, study hard,dont forget to bring along your calculator to your home.

### muiyuen

Points: 2
muiyuen said:
In my integrator design for a ramp output, i need a large resistance value of >500kΩ. Is there anyway to realize this large resistance instead of using a resistor, since resistors take up large die area? Can i use a MOS active load? Kindly advice...thanks!

I think external resistor maybe a good choice.
Also foundaries provide high resistance process, typically 1k ohms/sq. Still this will cost large area.
Active load may be not good enough, as it's linearity is a problem and long channel MOSFET has parastic caps or so. You can use it if you are sure they wont impact your application.:|

I did a filter whose fc=125Hz.

You can use a OTA with little gm to replace the Resistor! (gm=1/R)

ricklin said:
I think external resistor maybe a good choice.
Also foundaries provide high resistance process, typically 1k ohms/sq. Still this will cost large area.
Active load may be not good enough, as it's linearity is a problem and long channel MOSFET has parastic caps or so. You can use it if you are sure they wont impact your application.:|

Thanks for the feedback...if i used an external resistor, would there be any effect on the integrator operation, since it is external to the chip?

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