FDC2212: Why does FDC2212 not work when active shielding circuit is added into the output

Dengkuan Sun

Part Number: FDC2212

Tool/software:

Hi TI Experter,

I am using FDC2212 to design my proximity application. I would like to add active shielding to reduce signal interference. I am using the reference from TI experter to design the shielding circuit. You can refer to the link https://e2e.ti.com/support/sensors-group/sensors/f/sensors-forum/1478104/fdc2112-how-to-set-up-the-shield. I only connect the sensor into IN0A like your evm board. Now, I met an issue that I cannot see the signal IN0A from the oscilloscope when I connect the shielding circuit. Pls help this.

Thanks

Dengkuan

4 months ago

0 Patrick Simmons 3 months ago

TI__Mastermind 26335 points

Hello Dengkuan,

I am looking into your question now. Will try to have an update for you before close of business tomorrow.

0 Patrick Simmons 3 months ago in reply to Patrick Simmons

TI__Mastermind 26335 points

Hello Dengkuan,

From your prior post with John, I presume you have added a signal path to a BUF602 that is used for exciting your shield plate. Is that correct? Could you provide what your schematic looks like now that you have included shielding circuitry? Also can you provide a picture of your layout?

0 John Miller - Sensing 3 months ago in reply to Patrick Simmons

TI__Mastermind 40295 points

Dengkuan,

Could you provide a schematic of the circuit you are using to drive the shield, as well as the connections to the EVM?

Regards,
John

0 Dengkuan Sun 3 months ago in reply to John Miller - Sensing

Prodigy 240 points

HI Patrick and John

You can refer to my design. Now, FDC can work with active shielding. But, the signal amptitude with active shielding is only half of the signal without active shielding. Also, the detected proximity distance becomes small. Can you give some suggestions?

Thanks

0 John Miller - Sensing 3 months ago in reply to Dengkuan Sun

TI__Mastermind 40295 points

Dengkuan,

Does the frequency of the signal change with and without the active shielding connection?

Regards,
John

0 Dengkuan Sun 3 months ago in reply to John Miller - Sensing

Prodigy 240 points

Yes. the frequency without the active shielding is higher than one with shielding.

0 John Miller - Sensing 3 months ago in reply to Dengkuan Sun

TI__Mastermind 40295 points

Dengkuan,

It sounds like the active shield buffer may be loading the sensor/oscillator.

We have found that even a high impedance oscilloscope probe can distort the sensor waveform.
A trick we use is to connect a leaded 1k resistor to the tip of the oscilloscope probe and probe the PCB test point with the other end of the resistor.
Please give this a try if possible, and let us know the sensor frequency with and without the active shield connected?

Regards,
John

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FDC2212: Why does FDC2212 not work when active shielding circuit is added into the output