AFE4300 inconsistent BCM IQ measurements

Natefp

Other Parts Discussed in Thread: AFE4300

I have the eval kit as well as my own boards with the AFE4300. On my board I was able to communicate with the chip, enter both I and Q mode and take readings, however even when connecting a 10k resistor to IOUT and and connecting VSENSE to it, I get inconsistent results each time I read ADC_DATA_RESULT (for a given bcm frequency). I have a half second delay in my code that allows for settling time after switching modes. I currently switch to I, delay 5 ms, taking a reading, switch to Q delay 5 ms, take a reading print the results, and repeat. Attached is the data. Note that at some frequencies, like 250,000 kHz and 125,000 kHz the data is very consistent run to run, but at other frequencies, it varies wildly.

Thanks,
Nate

inconsistent data.xlsx

over 9 years ago

0 Praveen Aroul over 9 years ago

TI__Mastermind 49946 points

Hello Nate,

The device only supports body impedance range of 100 to 1 Kohm up to max of ~ 2.4 Kohms.

0 Natefp over 9 years ago in reply to Praveen Aroul

Prodigy 50 points

Thank you. I switched to a 470 ohm resistor and now I have one more frequency that is consistent (see sheet 2, attached). 31,250, 15,825, and 7813 kHz are still scattered. Any ideas?

3386.inconsistent data.xlsx

0 Natefp over 9 years ago in reply to Praveen Aroul

Prodigy 50 points

Any answer on this?

Here is another plot of my inconsistent data (BCM frequency on horizontal axis, output on vertical) :

0 Praveen Aroul over 9 years ago in reply to Natefp

TI__Mastermind 49946 points

Nate,

Do you see similar inconsistent results on the AFE4300 Evaluation module or do you only see this on your own board?

In IQ mode 125 Khz and 250 Khz freq. are not supported. There is a 2nd order low pass filter with filter corner freq of 150Khz at the output of the DDS.

The ADC codes are saturated for the 1Kohm resistor for 8, 16, 32 Khz BCM freq.
Could you check your register settings for the 4 BCM frequencies (8, 16, 32, 64 Khz)?

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AFE4300 inconsistent BCM IQ measurements