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how to decrease the noise from I/O Pads in design of LNA

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Junior Member level 1
Nov 8, 2005
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A problem encountered in my design of LNA.

The layout have finished and post-simulation is well.But the NF is bad when I add the models of I/O Pads into the post-simulation.

what can I do?How to get the ideal NF?

Thanks in advance!

The parasitics introduced by the I/O pads detune your LNA from the conjugate of Γ-optimum.
In your simulation you have to tune your LNA for best NF with these pads interconnected to your circuit.

There is not olny detuning but the PAD-IO model add substrate resistive loos to the input circuit. If you can select a PAD with metal shield under PAD metal it improve your NF.

Thanks for the explain of above, but could you tell me in detail?for example ,how to get best NF ?

Thanks a lot !

May be, you must remake your LNA design with I/O pad model. That's better

when u design LNA , u always design the input matching network for Γ optimum
which mean that it is the best input impedance for the noise matching this gives you the minimum noise figure

but u must take into account the model of the pad , the bond wire , and the package , and modify ur matching network with the new elements that have been added

wish this help


Make sure you are not using I/O pads for digital signals and bias from your design kit library. They contain ESD diodes and resistors that will kill your NF.

i think most of the design kits right now include pads for RF and analog circuits if the kit doesn't include these pads , so u have to create the Pads by ureself so u can control the capacitance of these pads

wish this help


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