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FDC2212: The ware of INA and INB

ttd
Mastermind 7670 points
Part Number: FDC2212

Dear Technical Support Team,

I'd like to simulate resonant circuit(LC tank) and the wave of electrode for ensuring the electrode and circuit design.

Could you tell me following questions?

【Questions】

What signal does INxA and INxB output to resonant circuit(LC tank)?

If you have any document , could you share it?

1.) Pulse wave or Sine wave?

2.) Voltage drive or Current drive?

3.) The amplitude of voltage or current

4.) drive time

Best Regards,

ttd

  • 0
    TI__Genius 11340 points

    Hi ttd,

    INxA is driven by a half sine wave, and INxB is driven by the same half sine wave shifted by 180 degrees. The amplitude of the half sine wave is determined by the drive current (IDRIVE register). You should adjust the Idrive setting so that the sensor oscillation amplitude is between 1.2V and 1.8V. You can refer to Table 9 in the FDC2212 datasheet for more information.

    Best,

    Jiashow

  • 0 in reply to Jiashow Ho
    Mastermind 7670 points

    Hi Jiashow,

    Thank you for your reply.

    I have some additional questions.

    I'd like to comprehend the principle of Excitation circuit. It is helpful to ensure the design of electrode and to simulate it on simulator.


    1.) Excitation circuit
    I guess that excitation circuit drives pulse of constant current and unnecessary frequencies are cut except for resonant frequency .
    Eventually,  I see a half sine wave, right?
    I'd like to comprehend this principle.

    If you show the figure of relationship between driving current and half sine wave, it is very useful to understand.

    2.) Driving time of current
    If excitation circuit drives pulse of constant current , how does it behave?
    Driving pulse of constant current continuously or driving current a certain period of time and stop latter.
    Otherwise, driving short or chopping current several times. 

    3.)Control INA and INB

    For example, FDC keep checking voltage of INA, and when this voltage reaches the some value(threshold), Does FDC change driving from INA to INB?

    4.) Drive current set by idrive
    For example: When setting idrive =11100, actually excitation circuit drives current of 1.006mA through INxA and INxB?

    Best Regards,

    ttd

  • 0 in reply to ttd
    Mastermind 7670 points
    Hi Jiashow,

    Thank you for your reply.

    I revised previous my post and please see below.

    ----------------
    I have some additional questions.
    I'd like to comprehend the principle of Excitation circuit. It is helpful to ensure the design of electrode and to simulate it on simulator.

    1.) Excitation circuit
    I guess that excitation circuit drives pulse of constant current and unnecessary frequencies are cut except for resonant frequency .
    Eventually, I see a half sine wave, right?
    I'd like to comprehend this principle.

    If you show the figure of relationship between driving current and half sine wave, it is very useful to understand.

    2.) Driving time of current
    If excitation circuit drives pulse of constant current , how does it behave?
    Driving pulse of constant current continuously or driving current a certain period of time and stop latter.
    Otherwise, driving short or chopping current several times.

    3.)Control INA and INB

    For example, FDC keep checking voltage of INA, and when this voltage reaches the some value(threshold), Does FDC change driving from INA to INB?

    4.) Drive current set by idrive
    For example: When setting idrive =11100, actually excitation circuit drives current of 1.006mA through INxA and INxB?

    Best Regards,
    ttd
  • 0 in reply to ttd
    TI__Genius 11340 points
    Hi ttd,

    The driving circuit provides current to resonate the LC tank which the FDC measures the frequency. The IDRIVE setting controls the amplitude of the oscillation with the following equation: IDRIVE = πVP ÷ 4RP.

    The FDC does not change the way it drives the circuit. As long as the RP and sensor frequencies are within the limits of the datasheet, it will drive the LC tank at its resonant frequency and convert the value to digital.

    Yes, excitation circuit drives current of 1.006mA through INxA and INxB with an idrive of 11100. Then the amplitude can be calculated with the formula above. Idrive should be adjusted until the amplitude is between 1.2V and 1.8V for best performance.

    Best,
    Jiashow
  • 0 in reply to Jiashow Ho
    Mastermind 7670 points
    Hi Jiashow,

    Thank you for your prompt reply.
    Could you answer following question?

    3.)Control INA and INB
    For example, FDC keep checking voltage of INA, and when this voltage reaches the some value(threshold), Does FDC change driving from INA to INB?

    Best Regards,
    ttd