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FDC2214: fdc2214

Ruchita Mishra
Prodigy 120 points

Part Number: FDC2214
Other Parts Discussed in Thread: LDC1614

Hi,

We are using FDC2214 in our  Medical project.

Will you please help me with the following doubts:

1) How to increase the dynamic range of of the sensor? (As the patient weight goes on increasing, the frequency goes on decreasing. Like for example  if we were measuring with 100 Kg Patient, frequency reduced to 5 Khz, Now if we want to measure 200 Khz we will get signal of very less amplitude which will be very difficult to measure and analysis )

2) Ways to reduce noise.

 Thanks,

Ruchita 

  • 0
    TI__Genius 17440 points

    Hi Ruchita,

    Could you describe your application in more detail? I am not sure what your sensor configuration is like.

    The best way to reduce noise is to maximize the RCOUNT register setting (which minimizes the sample rate) and to use an external oscillator with low jitter.

    Best Regards,

  • 0 in reply to Kristin Jones93
    Prodigy 120 points

    Hi Kristin,

     Attached file shows the configuration of sensor. In place of Variable Capacitor we are using Capacitive Sensor sheet.

    Drawing1.pdf

  • 0 in reply to Ruchita Mishra
    TI__Genius 17440 points

    Hi Ruchita,

    The minimum frequency that the FDC2214 can drive is 10kHz. I recommend keeping your sensor frequency away from the absolute minimum frequency. You can change this by simply reducing the fixed inductance in the LC tank. In general, capacitive sensing responses are strongest when the target is grounded. It sounds like you have a specialized sensor, so this may not be an option for you. Otherwise, you may need to use multiple drive current settings to keep the sensor oscillation amplitude within the optimal range across the full capacitance range of your sensor. You may find this application note helpful for setting the drive current. Though this app note is for inductive sensing, the drive current settings are still applicable to the FDC2214.

    Best Regards,

  • 0 in reply to Kristin Jones93
    Prodigy 120 points

    Hi Kristin,

    Thanks for your reply. It was helpful.

    Kindly look into the changed Sensor configuration file with respect to yesterday.

    Secondly I want to know whether my length of the wire will affect the noise. We are using the length of 390 mm from connector to 8th segment sheet. If this is the case please let me know  the Maximum length of the wire which can be used for minimum noisy signal.

    Sensor Configuration file is attached for your reference. Kindly go through it and tell me whether any modification is needed for less noisy signal and to increase the dynamic range of the signal.

    As you suggested previously, just for your information we are using an External Oscillator only of 40 Mhz. Can you suggest any other method of reducing noise?

    Regards,

    Ruchita Shreeram Mishra

  • 0 in reply to Ruchita Mishra
    Prodigy 120 points

    Hi,

    Sorry I missed the attachment. Kindly find the attachment below.

    Regards,2543.Drawing1.pdf

    Ruchita Shreeram Mishra

    Fullscreen Configuration.txt Download 
    

INIT_CONF_2A = 0X3E01  Address 0X1A // Setting the slave to sleep mode to configure the registers

RCOUNT_CH1 = 0X0FFF  Address 0x08
RCOUNT_CH2 = 0X0FFF  Address 0x09
RCOUNT_CH3 = 0X0FFF  Address 0x0A
RCOUNT_CH4 = 0X0FFF  Address 0x0B

CH0_OFFSET = 0X0000  Address 0x0C
CH1_OFFSET = 0X0000  Address 0x0D
CH2_OFFSET = 0X0000  Address 0x0E
CH3_OFFSET = 0X0000  Address 0x0F

SETTLECOUNT_CH0 = 0X0400  Address 0x10
SETTLECOUNT_CH1 = 0X0400  Address 0x11
SETTLECOUNT_CH2 = 0X0400  Address 0x12
SETTLECOUNT_CH3 = 0X0400  Address 0x13

CLOCK_DIVIDERS_CH0 = 0X1001  Address 0x14
CLOCK_DIVIDERS_CH0 = 0X1001  Address 0x15
CLOCK_DIVIDERS_CH0 = 0X1001  Address 0x16
CLOCK_DIVIDERS_CH0 = 0X1001  Address 0x17

ERROR_CONFIG = 0X0001  Address 0x19

MUX_CONFIG = 0XC20C  Address 0x1B

DRIVE_CURRENT_CH0 = 0X8800   Address 0x1E
DRIVE_CURRENT_CH1 = 0X8800   Address 0x1F
DRIVE_CURRENT_CH2 = 0X8800   Address 0x20
DRIVE_CURRENT_CH3 = 0X8800   Address 0x21

INIT_CONF_2A = 0X1C01  Address 0X1A // Setting the slave to active mode 

///////////////////////////////////////////////////////

INIT_CONF_2B = 0X3E01  Address 0X1A // Setting the slave to sleep mode to configure the registers

RCOUNT_CH1 = 0X0FFF  Address 0x08  
RCOUNT_CH2 = 0X0FFF  Address 0x09
RCOUNT_CH3 = 0X0FFF  Address 0x0A
RCOUNT_CH4 = 0X0FFF  Address 0x0B

CH0_OFFSET = 0X0000  Address 0x0C
CH1_OFFSET = 0X0000  Address 0x0D
CH2_OFFSET = 0X0000  Address 0x0E
CH3_OFFSET = 0X0000  Address 0x0F

SETTLECOUNT_CH0 = 0X0400  Address 0x10
SETTLECOUNT_CH1 = 0X0400  Address 0x11
SETTLECOUNT_CH2 = 0X0400  Address 0x12
SETTLECOUNT_CH3 = 0X0400  Address 0x13

CLOCK_DIVIDERS_CH0 = 0X1001  Address 0x14
CLOCK_DIVIDERS_CH0 = 0X1001  Address 0x15
CLOCK_DIVIDERS_CH0 = 0X1001  Address 0x16
CLOCK_DIVIDERS_CH0 = 0X1001  Address 0x17

ERROR_CONFIG = 0X0001  Address 0x19

MUX_CONFIG = 0XC20C  Address 0x1B

DRIVE_CURRENT_CH0 = 0X8800   Address 0x1E
DRIVE_CURRENT_CH1 = 0X8800   Address 0x1F
DRIVE_CURRENT_CH2 = 0X8800   Address 0x20
DRIVE_CURRENT_CH3 = 0X8800   Address 0x21

INIT_CONF_2B = 0X1C01  Address 0X1A // Setting the slave to active mode

  • 0 in reply to Ruchita Mishra
    TI__Genius 17440 points

    Hi Ruchita,

    There is definitely a maximum distance that the LC tank can be placed away from the FDC2214, based on the sensor frequency. Longer cables also increase the possibility of EMI coupling into the system. If you'd like to check the maximum distance between your sensor and your device, I recommend using the "LDC131x-LDC161x_Config" tab in this excel tool. The LDC1614 has the same drive capabilities as the FDC2214. 

    The only other way to reduce noise is to minimize your sample rate (maximize RCOUNT).

    Best Regards,

  • 0 in reply to Kristin Jones93
    Prodigy 120 points

    Hi Kristin,

    Can you please tell me how to calculate Sample rate from RCOUNT value and how are they related?

    Thanks,

    Ruchita Shreeram Mishra

  • 0 in reply to Ruchita Mishra
    TI__Genius 17440 points

    Hi Ruchita,

    Please see section 9.3.2 of the datasheet for more information about RCOUNT and how it relates to the sample rate.

    Best Regards,