Comments on How to protect RF switches from ESD?
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How to protect RF switches from ESD?
Assume that I have some generic antenna connector, followed by a pi-filter/50ohm impedance matching components, then a DC blocking cap (as per the RF switch recommendations) and then a RF switch for split tx/rx semiduplex transceiver, as in this schematic:
How do I best protect this RF switch from ESD coming in from human fingers touching the antenna connector? I need the highest ESD class (4) of the IEC61000−4−2, meaning 8kV contact discharge, 15kV air discharge.
I'm considering a specialized "ultra-low capacitance" TVS diode such as ESD8472 (rated up to 20kV), which is bidirectional.
Questions:
- Is this TVS diode the way to go?
- If so, where do I place it in this schematic? Directly on the antenna or somewhere else?
- How to determine the suitable breakdown voltage? I'm assuming it should be based on the RF switch supply which is 3.3V.
Post
Somewhat a pity to throw money for an expensive ultra-low capacitance TVS.
You have not specified what is the frequency range of your antenna system, but since you say you have to protect it from human fingers, it is likely to be a small antenna in the gigahertz range.
So, all what you need is a small, small, choke between C3 and S1, connected to ground via a stupid TVS, or even without TVS at all (since the the DC voltage between C3 and S1 is most probably at ground). Totally inexpensive.
Of course, you choose the inductor value to block 95% (say) of the lowest frequency in the given range and no more, which means a very small inductance at these frequencies. ESD discharges are much slower (in the MHz range at the worst), and after they have passed the pi filter, they will probably come much likely in the 100KHz range maximum. So, they will discharge to ground via the TVS, and hardly feel the small choke.
Note: many antennas, like the Vivaldi antenna or the self grounded bow tie antenna are made of a single block where the ground part is connected to the feeding part:
For those antennas, I believe it is pointless to protect the receiver from ESD.
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