CC1310: Crystal drift with wide temperature swings (0C to 80C)

dorse

Part Number: CC1310

Hi, we have several boards as temperature sensors where there temperature can go from 0C to 80C and the receiver temperature is only between 10C and 40C.

We are using the same crystal as the Launchpad (EPSON). The frequency varies a lot with the temperature (drift) and we are using the LRM so the bandwith is small. I have a couple questions:

1. What can I do to make this more robust (maybe there is a firmware based solution)?

2. Do you have any crystal recommendation where tempeatures can have big changes? I know the CC1310 doesn't support a TCXO so that's not an option.

Any suggestions?

Thanks!

over 8 years ago

0 PrashanthS over 8 years ago

TI__Expert 8765 points

Hello Dorse,

If TXCO is not an option, one thing you can do is to create a crystal frequency error table (typically called an "S" curve) by measuring the error in the frequency through the temperature range. You can then use the reading from temp sensor and adjust for this offset in firmware to obtain a more accurate output frequency. It is possible that the crystal manufacturer provides you with this "S" curve.

We did this on one of our applications, below is a code snippet. It also does interpolation to obtain a more accurate error from the S curve.

#include "aon_batmon.h"

#define SCURVE_ARRAY_SIZE 25

int16_t freqTempCurve[SCURVE_ARRAY_SIZE] = {
-12901, //-40
-9295, //-35
-5689, //-30
-2788, //-25
-64, //-20
1607, //-15
2564, //-10
3259, //-5
3279, //0
2948, //5
2416, //10
1532, //15
310, //20
-967, //25
-2244, //30
-3357, //35
-4167, //40
-4777, //45
-5309, //50
-5408, //55
-5008, //60
-4167, //65
-2724, //70
-1182, //75
321, //80
};



#ifdef FREQ_TEMP_COMPENSATION
tempDegC = AONBatMonTemperatureGetDegC(); // Read temperature
#ifdef FREQ_TEMP_INTERPOLATE
tempDegC_floor = tempDegC - (tempDegC % 5);
freqTempCurveIndex = (int)(tempDegC_floor + 40) / 5;

if (tempDegC >= 0)
freqError = (freqTempCurve[freqTempCurveIndex + 1] - freqTempCurve[freqTempCurveIndex]) * ((float)( tempDegC - tempDegC_floor)/5);
else
freqError = (freqTempCurve[freqTempCurveIndex - 1] - freqTempCurve[freqTempCurveIndex]) * ((float)( tempDegC - tempDegC_floor)/5);

freqError = freqTempCurve[freqTempCurveIndex] + freqError;

ul_Freq = (ul_Freq - freqError);

#else
if (tempDegC >= 0) // Round by 5 degrees
tempDegC = ((int)((tempDegC + 2.5) / 5)) * 5;
else
tempDegC = ((int)((tempDegC - 2.5) / 5)) * 5;

freqTempCurveIndex = (int)(tempDegC + 40) / 5;

ul_Freq = (ul_Freq - freqTempCurve[freqTempCurveIndex]); // Compensate for error from the curve.
#endif
#endif

   tempDegC = ((int)((tempDegC - 2.5) / 5)) * 5;

freqTempCurveIndex = (int)(tempDegC + 40) / 5;

ul_Freq = (ul_Freq - freqTempCurve[freqTempCurveIndex]); // Compensate for error from the curve.

#endif

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CC1310: Crystal drift with wide temperature swings (0C to 80C)