LDC1312EVM: LDC1312

Hi Filipe,

Can you attach your image? It did not appear in the post.

Also, can you provide a scope trace showing about 10 cycles of the sensor? Make sure your sensor amplitude is >0.8V (and optimally >1.2V) when the target is at its closest position. This is controlled by the IDRIVE setting for the device.

Also, make see if you can increase the RCOUNT value; which can also help reduce noise.

Regards,
ChrisO

Hello Chris O.,

First of all thank you for your reply. The image containing the signal is attached. 

In this case I'm setting the Rcount is 8500. I decided to insert this value because is about 13 bits. With 8500 I get a sample 6.56 ms and if I set the Rcount with 65535 I have 16 bits, but the time of sample is 65 ms.

According datasheet the maximum amplitude is 1.5V. I set the IDRIVE in code 3.

If you have more questions, please let me know.

Best Regards

graph_M5_M6.pdf 

Hi Filipe,

The maximum drive amplitude is actually >1.8V; the recommended sensor amplitude is 1.5V.

If you checked the sensor amplitude with no target, using an IDRIVE of 3 implies you have an Rp of ~51k; and an AC Rs of ~12ohms. To shift up to 224MHz, the inductance would need to drop to 150uH, and so your Rp might be down to ~4k; and so your sensor amplitude is going to be too low. Please check the sensor amplitude with the target present.

You may want to try the automatic sensor amplitude control of the LDC131x; this functionality can dynamically correct the sensor amplitude, but may cause some unexpected jumps in response. For debugging your issue, it should be fine to use. Set RP_OVERRIDE to 0 and AUTO_AMP_DIS to 0.

Once you have the sensor amplitude set correctly, then you can reduce the RCOUNT setting until its affect on the noise is still ok.

Regards,

ChrisO

Hi Chris O.

Thank you very much for your reply.

Le me know one thing. According the datasheet of LDC1312EVM there is a filter before LDC as the following drawing:

The capacitors were calculated according the capacitor C = 330 pF. The target is to use a low frequency because the coil goes into a stainless steel tube.  The magnetic field must overtake this tube and It should be enough to detect a target. So in this case the better oscilation frequency is about 70 KHz. I would like to calculate the capacitors with this oscilation frequency.

Do you have any ideia to calculate the capacitors for that oscilation frequency?

Thank you very much

Hi Chris O.

Sorry, but the drawing you can see now.

Best Regards