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Design >> Analog Design >> MIM Capacitor Tutorials & Errors
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Message started by SenthilRajan on Jan 24^th, 2017, 8:37pm

Title: MIM Capacitor Tutorials & Errors
Post by SenthilRajan on Jan 24^th, 2017, 8:37pm

Dear all,
i doing layout for OTA with feedback,
in that i am using 15pF MIM capacitoance using UMC180nm Technology
file.i generated 15pF MIM capacitance using 10x10 matrix of 150fF MIM
capacitance(all are connected parallel) to improve matching to obtain
gain of 100.when i run the post-layout simulation during lower
frequencies the AC analysis output waveform is not same as pre-layout
simulation results.need help to resolve this error.

Title: Re: MIM Capacitor Tutorials & Errors
Post by ULPAnalog on Jan 25^th, 2017, 1:19am

Is it a capacitive coupled amplifier? If so, is this 15pF input capacitance or the feedback capacitance?

Extracted netlist generally does not have mismatch enabled and needs to be explicitly added (in most cases). Therefore the issue might not be related to mismatch but rather due to parasitics. Moreover good matching practices include laying both feedback capacitance and input capacitance in a common centroid fashion and adding dummies to create similar looking environment for all caps.

Please post the schematics, pre and post layout sims, including the extraction type (C+CC or R+C+CC) to better understand the problem.

Title: Re: MIM Capacitor Tutorials & Errors
Post by SenthilRajan on Jan 25^th, 2017, 9:19pm

Yes the circuit is capacitive coupled instrumentation amplier.15pF capacitance is input capacitance and 150fF capacitance is feedback capacitance,i did RC extration.if i have to include dummy capacitance,what value i have to include in capacitance layout.if possible where i have to refere for tutorials?

Title: Re: MIM Capacitor Tutorials & Errors
Post by ULPAnalog on Jan 26^th, 2017, 1:38am

There are several documents available on the web detailing good layout practices for matching passives. One of those is http://www.eecg.toronto.edu/~johns/ece1371/slides/ECE1371_Mismatch-2.pdf

Since you have a differential amplifier at hand, you need to match sensing electrode and reference electrode paths to avoid cm-dm conversion.

Use of mos devices as pseudo resistors, while is a common practice in biopotential amplifiers, their modelling is rather poor under such operating conditions.

Title: Re: MIM Capacitor Tutorials & Errors
Post by SenthilRajan on Jan 27^th, 2017, 5:18am

Thank You the link material helped lot..i got same output for pre-layout and post-layout..thank you once again

Title: Re: MIM Capacitor Tutorials & Errors
Post by ULPAnalog on Jan 28^th, 2017, 11:01am

Good to know that you got it working. If you could post the problem and its solution, it would help others who might run into similar issue in future.

Best regards