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jovial Junior Member Offline Posts: 19	how to implement a resistor of value around 450M ohms on chip May 30^th, 2014, 10:49pm HI, I want to how to implement a resistor of value around 450M ohms on chip. I am working on UMC 180nm technology. Can anyone suggest me a simple MOS based circuit for the same?
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loose-electron Senior Fellow Offline Best Design Tool = Capable Designers Posts: 1638 San Diego California	Re: how to implement a resistor of value around 450M ohms on chip Reply #1 - May 31^st, 2014, 2:49pm Simply put - redesign your circuit or method Anything that uses a resistance value that large will not be reliable.
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cchen New Member Offline Posts: 8	Re: how to implement a resistor of value around 450M ohms on chip Reply #2 - Jun 4^th, 2014, 1:23am If available in your design, trim by digital code may be a choice.
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sheldon Community Fellow Offline Posts: 751	Re: how to implement a resistor of value around 450M ohms on chip Reply #3 - Jun 5^th, 2014, 3:25pm CChen,
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sheldon

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Posts: 751

Re: how to implement a resistor of value around 450M ohms on chip
Reply #4 - Jun 5^th, 2014, 3:41pm

Jovial,

A value of 450 MegaOhms is a very large value to try to integrate.
Typical diffused and poly silicon resistors have relatively low sheet
resistances, which implies long, thin resistors. Not sure what value
of sheet resistance the process has. However, even assuming a very
high sheet resistance of 10kOhm/sq, means that the resistor would
require 45,000 squares to realize. In addition, to the resistor, you
will probably need guard rings around the resistor to prevent
leakage further increasing the area. BTW, the 10kOhm/sq assumes
the process has a pinched resistor which means that there is a very
limited voltage range of operation for the resistor. More practical
diffused and poly resistors have sheet resistances on the order of
~100 Ohms/sq. Which implies ~1M squares of resistance. Loose
Electron is correct, a design requiring a 450MOhm resistor implies
that the design is not appropriate for integration.

Best Regards,

Sheldon

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rf-design

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Reiner Franke

Posts: 165
Germany

Re: how to implement a resistor of value around 450M ohms on chip
Reply #5 - Jun 6^th, 2014, 1:32am

jovial wrote on May 30^th, 2014, 10:49pm:

HI,
I want to how to implement a resistor of value around 450M ohms on chip. I am working on UMC 180nm technology.
Can anyone suggest me a simple MOS based circuit for the same?

I suggest to change the implementation of the functional element which need the 450M resistor.

The current from a 0.18u max supply of 1.8V on this 450M resistor is 4nA. So this is not far away from leakage currents of the active devices. So the total accuracy comparing leakage and signal is not high. Furtheron the a 450M with 2k/sq high ohmic poly need 225000sq so that the parasitic cap of this resistor could create stability issues if used in an amplifier feedback configuration.

An alternative for the function "low current over signal voltage" could be using a much smaller resistor and an active current division. So the total function is a transconductive element with output stage current scaling.

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loose-electron Senior Fellow Offline Best Design Tool = Capable Designers Posts: 1638 San Diego California	Re: how to implement a resistor of value around 450M ohms on chip Reply #6 - Jun 6^th, 2014, 6:17pm What is it that you are trying to do that requires such a device? I am sure that there is a better way or method.
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