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CC1200 - Auto calibration in 4 -GFSK

Other Parts Discussed in Thread: CC1200, CC1120

We are  using  the CC1200 with the following  main parameters:

1. Bit rate of data is: >= 500 kbps

2. Modulation format = 4-GFSK.   

3.  Packet length mode = Infinite , changed to fix when  the rest of packet is less  256 Bytes.

4.  Deviation :0.3 of the bit rate approx. 

5. The protocol: one packet from A to B  and then one packet in opposite from B to A  and again. 

6. The length of preamble : 4 bytes. 

In lower than 500 kbps bit rate,  the PER is very good. 

The problem :

When the  auto-cal for FS is turn On, the PER is very bad regardless of the signal level.

But when it turn off, The  PER is an acceptable  

At rate of 500 kbps with the Modulation format:  2 -GFSK is  working fine,  even when the  auto-cal is On.

Beyond the 500 kbps bit rate , there is not option to work other than  4-GFSK. 

Is there any explanation  why is it  not good working   when the auto cal is turn on in 4- GFSK  ?

What should be the corrected setting ?

Maybe there is another wrong setting ? 

What should by the recommended stability of the oscillator when the auto calibration is turn off ?   

By using TCXO of the stability of +- 2 ppm over the temperture range, is good enough to tun off the auto calibration ? 

I  appreciate your clarification. 

B.R.

Yoram

  • - You need to calibrate. This is calibration of the VCO and is independent of your external clock source.

    - After you have calibrated, how does the spectrum look like? Do you operate on the correct frequency?

    - Note that the deviation you have selected is small. The deviation given is given for the outer symbols, the inner symbols is 1/3 of that. Hence the modulation index for the inner symbols is very small in your case and should be increased, see the suggested SmartRF Studio settings for 4- GFSK

  • - The frequency is correct. I test the system from very low bit rate to 1 Mbps. 

    - As I have mentioned,  till 500 Kbps 2 GFSK it is  work good.

    - The problem start from 500 Kbps 4- GFSK to 1 Mbps 4- GFSK

    - I have used SmartRF setting, but it doesn't work properly. 

    - Could you send the complete corrected  configuration for 500 Kbps for 4 -GFSK ?

    - My external clock source  39.0 Mhz. 

    - What should be the deviation for 500 kbps 4- GFSK ? Deviation of ~200 K is not enough ?  

    - Why is depended of the calibration ? 

    - Is it not enough to calibrate only once after power on, if the frequency  is not changed till power off ? 

    B.R. 

  • Maybe I didn't understand you, What is the meaning "Do you operate on the correct frequency" ? 

    Are there any limitation of  specific frequencies in the band  ?

    Please advice 

    B.R

  • For 500 kbps, 4 GFSK, have you tried the SmartRF Studio settings (400 kHz deviation?) If so, what do you mean by "not properly"?

    If you plan to use a different rate, please let us know and I can test some and provide you with a register set.

    Correct frequency: If you send a CW, do you get this within ~10 kHz of the programmed frequency? This will most likely not cause the issues you are seeing since 2-(G)FSK works fine.

    Note that the result of the calibration will be dependent on supply voltage and temperature hence it is good practice to calibrate either each time going into Rx/ Tx or at regular intervals. 

  • Thank You ! 

    - I didn't try 400 khz deviation and I will try it.

    - "not properly " means there are unacceptable PER - more than 10%,  regardless of the power level. 

    The length of packets are short ~ 20 Bytes. 

    - " CW" - do you  mean to send data in 4-GFSK with auto cal. and then to stop sending data with modulation

    and to  send CW instead ? Please clarify.

    - I plan to use the following rates :  500 kbps , 750 kbps and 1Mbps.

    I will appreciate it very much if you send me the setting of registers.

    B.R.

  • 500 kbps and 1Mbps, use the settings from Smart RF Studio. 750 kbps, start from 1 Mbps settings and set the datarate to 750 kbps. I tested with deviation equal to 300 kHz which gave good results.

  • hi 

    What  is the best way and configuration to send exactly 256 bytes  in the packet ? 

    In the TI document it is mention only  less or higher than 256 bytes in packet. .

    Please advice.

    Yoram

  • Please see the infinite packet length example here: http://www.ti.com/lit/zip/swrc253 The safest is to view 256 byte the same way as larger packets.

  • hi, 

    Could you send me the errata note about the calibration ? it is mention in the document. 

    Could you send me the full errata document ? 

    B.R.

    Yoram

  • Sorry I should have been more precise in my last mail.

    The software example I pointed to is for CC1120 which need a calibration errata for a given version of the chip. For CC1200 you don't need the errata. Use the concept from the example, not the CC1120 based detail.