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Design >> RF Design >> Ground Plane in RFIC
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Message started by sriram on Sep 26^th, 2013, 2:46pm

Title: Ground Plane in RFIC
Post by sriram on Sep 26^th, 2013, 2:46pm

I need some advise on the ground plane connection in Silicon RFICs for mm-wave circuits. The problems are the following:
1. Your RF ground comes only from the RF probe, say you have a PA, your input probe and output probes are GSG and the ground is calibrated on these probes. Your DC grounds don't matter as they are wirebonded to a PCB which essentially makes them AC open.
2. Silicon is not a good ground. Even though you may have a substantial number of substrate contacts, there is resistance/inductance between these contacts.

Keeping these in mind how do you suggest to make a layout that has a good ground reference.

Thanks
Sriram

Title: Re: Ground Plane in RFIC
Post by raja.cedt on Sep 27^th, 2013, 3:31am

dear Sriram,
1. Ground connection will never be an ac open, Bondwire inductance must be small enough to create ac ground over there, moreover Differential circuits have less ac current on top of that decaps will take care of that ripple.

2. this is not so clear to me, For Rf transmission line no body use substrate as an ground, use one metal as a ground plane (of course you have to grid to get rid of DRC and density). For Transistors substrate ground is fine.

Thanks,
Raj.

Title: Re: Ground Plane in RFIC
Post by sriram on Sep 27^th, 2013, 11:16am

Hi raja,
1. The bondwire inductance is approximately 1nH which is around 600 Ohms at 100GHz. So essentially it is an open. Hence a ground connection through the PCB is going to be an open at 100GHz.
2. Transmission lines always do have a metal ground plane. But how does this metal ground plane connect to a global ground. I believe there is substantial inductance between this ground plane and the global ground. How do you minimize this inductance?

Thanks
Sriram

Title: Re: Ground Plane in RFIC
Post by raja.cedt on Sep 27^th, 2013, 11:48am

Don't forget about decaps, At 100G decaps will supply full current, hence you don't need to consider 100G for your bond wire.