Target impedance is violated in Decoupling analysis ,when simulated in Cadence PDN

[sudhagar_k@hcl.com]

Hi,
In my simulation in Cadence PDN for decoupling analysis , there are 6 bulk caps and 23 small caps ranging from 0.001uF to 0.47uf. The result shows violation of target impedance for that particular volt rail of 1.2V in 10-100MHZ frequency range.
I tried to add some more decaps with smaller values, but its reducing the target impedance of the voltage rail rather than increasing it.
What all can be done. Please advise.

 

[BradtheRad]

The simulator I use generates an error if I connect two capacitors in series, with both wires containing only the capacitor.

To prevent the error I must install a resistor in one or both wires, inline with the capacitor. The resistor can be very low ohms.

Some errors appear to have no cause that I see. Often I must install resistors in odd places, to prevent an error.

 

[sudhagar_k@hcl.com]

The simulator I use generates an error if I connect two capacitors in series, with both wires containing only the capacitor.

To prevent the error I must install a resistor in one or both wires, inline with the capacitor. The resistor can be very low ohms.

Some errors appear to have no cause that I see. Often I must install resistors in odd places, to prevent an error.

Am not getting you Brad.
Am asking ways to reduce the impedance of the capacitors or to increase the target impedance of the board

 

[dehati]

What you may like to do is calculate the impedance using a spread sheet and see if it matches the impedance given by the Cadence. Use the following as a guide.

http://referencedesigner.com/books/si/bypass-cap-power-supply.php