LimeUtil Calibration fails at certain frequencies and path combinations

System Development
1

Hi guys,
I am using LimeUtil to calibrate my custom board based on LMS7002M LimeSuite library modified for SPI connection . Firstly,I have made following modifications to LimeUtilCalSweep.c.
a) Changed the reciever path to LNAH in Rx and changed the transmitter path to Band2 in Tx .
b) Set the reference frequency to 40MHz .
c) Replaced LMS_SetLOFrequency to LMS_SetClockFreq
I get the following errors -
a) MCU calibration fails for Channel A , Channel B RX and Channel A TX.(Signal too weak or not connected) . It only passes for Channel B TX .
EDIT:There was a problem with channel configuration . Now it fails for RX path LNAH for both Channel A and B.

What could be the reason for this strange behaviour ?

2

Hi , I just found something .
LNAH calibration .
This tells that LNAH cannot be used for automatic calibration . Is this true for LimeSuite in general?

3

Hi @kishores,

Here is no loopback path to LNAH from Tx Band2 inside of LMS7002M. You can have these combinations:

  1. Tx Band1 to LNAH;
  2. Tx Band1 to LNAW;
  3. Tx Band2 to LNAL.

Check Programming and Calibration Guide, sections “RFE Control Diagrams” and “TRF Control Diagrams” for more information.

5

Hi @Zack, I am trying to calibrate over frequencies 2.2GHz to 2.3GHz . LNAH is not working with any combination with Band1 in this range . What should I look into at this point ?

6

Hi @kishores,

Do you have a possibility to save register values in LimeSuite format?

7

@Zack , Link to config file . This is the configuration of registers . I think you would have to remove last 3 lines if you have to upload it

8

Do you use the same frequency for Tx LO and Rx LO?
You use internal LDOs. Is this intended?

9

@Zack

Do you use the same frequency for Tx LO and Rx LO?

Yes, I used same frequency for TXLO and RXLO .

You use internal LDOs . Is this intended?

Yes, I am using internal LDOs . Could that be the issue ?

Another question,
Is SXR and RX_LO the same or different ?

10

Then use SXT only:

  1. Uncheck “LO buffer from SXT to SXR” in SXT tab in “Power down controls” group;
  2. Check “VCO” in SXR tab in “Power down controls” group.

No, just want to be sure you are not using these together with external ones.

These are the same.

11

@Zack , I am using LimeSuite library on headless server and hence my system has no GUI . I tried your suggestions by writing directly to the LMS register . I am using the function LMS_WriteLMSReg(device,0x011C,0xA943) .
Meanwhile, I tried with other start and stop frequencies(400MHz to 500Mhz). The result is the same . It always fails for the combination LNAH , Band1 .

12

Hi @Zack ,
Sorry to disturb you but could you provide some input on this issue .

Meanwhile, I tried with other start and stop frequencies(400MHz to 500Mhz). The result is the same . Calibration always fails for the combination LNAH , Band1 .

13

Hi @kishores,

We tried your configuration file on LimeSDR-Mini and it works fine. Probably there is an issue in your hardware.

14

Thanks @Zack for your reply . What could be the issue though ? If the clock is not exactly 40MHz could that cause problems ?

15

Hi @Zack,
The hardware is quite similar to Lime Mini . We are able to do most of the things but calibration for LNAH is crucial .
I can send you the schematics and PCB design files if you want them in your personal mail .

16

Hi @kishores,

OK, send schematics via PM, please.