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TIDM-CAPTIVATE-THERMOSTAT-UI: About CapTIvate sensor electrode tightly coupled

GR
Genius 3186 points

Part Number: TIDM-CAPTIVATE-THERMOSTAT-UI

Hi

My costomer have a question about CapTIvate reference designe.

In This document, 4.3.4 Electrode Geometry

--
Capacitive Touch Thermostat User Interface With CapTIvate TmTechnology


https://www.ti.com/lit/ug/tiduav1/tiduav1.pdf 

--

"A ground plane is placed in the center of the sensor to keep the Rx and Tx electrode tightly coupled. The tight coupling that is forced between the two electrodes improves their resistance to external noise and allows for buttons which use this design to be spaced close together."

is witten.

Question1 : How to a ground plane effect RX and TX electrode tightly coupled.

I think fill RX pattern is good for big sensor capasitance between TX snd RX .

Question2 : The tight coupling (by a ground plane) is forced between the two electrodes improves their resistance to external noise. because TX-GND and RX-GND capacitance can be increased, So The level of noise in the sensing is relatively small compared to the voltage amplitude that the parasitic capacitance imparts to the sensing.
Is this correct?

Question3 : "Electrode tightly coupled" is improved by remove RX pattern section that can get capacitance less than another(Not removed) section?

Thanks,

GR

  • 0
    TI__Mastermind 40085 points

    I would suggest your cusotmer read this document first: https://www.ti.com.cn/cn/lit/ug/slau857a/slau857a.pdf. The first paragraph will tell you what is capacitive touch. 

    Q1: Ground plane can help absove the noise in the air. It is like a shilder to the TX and RX line.

    Q2: Idealy, it is not right. Becuase the detected capacitance is TX-RX capacitance. That means the TX-GND and RX-GND capacitance will not affect the sensitivity too much.

    Q3: Yes, because, you are increase the d and reduce the A, the TX-RX capacitance is reduced.

  • 0 in reply to Eason Zhou
    Genius 3186 points

    Hi Eason,

    Thank you to your support.

    In Q3,I have one Question,

    In The reference designe document, "The tight coupling that is forced between the two electrodes improves their resistance to external noise" is written.

    I think The tight coupling(close between TX and RX) improve increasing TX-RX capacitance.

    For increasing TX-RX capacitance, I think good for Fill RX pattern square.
    However this designe had removed center part of the edge in RX pattern.

    So designe reducing TX-RX capacitance.

    Could you tell me why removed?

    Thanks,

    GR

  • +1 in reply to GR
    TI__Mastermind 40085 points

    Hi GR,

    Because the elecrtical traces are mostly at the closest distance between TX and RX pannel. So adding RX at the center will not increse the capacitance too much. Actually, to reduce the noise influence, the one solution is to make the sensor to be closed with GND.

    Eason

  • 0 in reply to Eason Zhou
    Genius 3186 points

    Hi Eason,

    I understood that adding RX at the center will not increse much capacitance. 

    And Closing sensor with GND is one good way to reduce the noise influence.

    Thank you very much for your support!

    Best Regards,

    GR

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