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LMX2820: Instant calibration when frequency hopping between different VCO banks

Yao-Hua
Prodigy 120 points
Part Number: LMX2820
Other Parts Discussed in Thread: LMX2595

Hi, Team :

What's the exact procedure with instant calibration when switching from VCO1 to VCO6?

In the specification of LMX2820, it states as the below.

==========================================================

To change frequencies after the instant calibration is initialized:
1. Write the values for INSTCAL_PLL_NUM, PLL_N, PLL_NUM, PLL_DEN.
2. Write R0 to trigger Calibration (with DBLR_CAL_EN = 0, FCAL_EN = 0).

==========================================================

Do we need to program VCO_SEL when it changes from VCO0 too VCO6?

Could you please show the whole procedure step by step using instant calibration (VCO1 -> VCO6)?

Regards,

Yao-Hua

  • +1
    TI__Mastermind 33770 points

    Hi Yao-Hua,

    Please check the application note Dramatically Improve Your Lock Time with Vco Instant Calibration (snaa342), we describe instant calibration in detail in section 4.3. Instant calibration does not require setting VCO_SEL or any other full-assist calibration values, those are loaded automatically.

    The whole procedure step by step for instant calibration is captured by the datasheet, section 8.1.3, from which you copied the above segment.. There are no other steps. Can you clarify for me what else you're looking for?

    Regards,

    Derek Payne

  • 0 in reply to Derek Payne
    Prodigy 120 points

    Hi, Derek :

    I have studied snaa342 document, but it doesn't specify the programming sequence in detail.

    To use row 2 in Table 4-2 as an example, the frequency changes from 6000MHz to 5063MHz.

    VCO changes from VCO1 to VCO6 and the table shows the lock time measurement only.

    This document doesn't show the complete programming sequence for each row.

    To use row 2 as an example (VCO1 -> VCO6), could you please show the programming sequence?

     

    Regards,

    Yao-Hua

  • 0 in reply to Derek Payne
    Prodigy 120 points

    Hi, Derek :

    I still have two questions below.

    (1) The whole procedure for instant calibration is only two steps as captured above even change to different VCO?

          I wonder this procedure works for frequency hopping in the same VCO or can be between different VCOs.

          No matter the same VCO or between different VCOs, does this procedure always work?

    (2) LMX2820 data sheet doesn't give the estimation formula of VCO_CAPCODE & VCO_DACISET.

          I can't use partial assist method without this formula. Is the formula the same as LMX2595?

  • +1 in reply to Yao-Hua
    TI__Guru** 108480 points

    Hi Yao Hua,

    Here is the test procedure:

    1. Open TICS Pro and select EVM default mode configuration
    2. In User Controls page, check all Double Buffer bits
    3. In PLL page, uncheck DBLR_CAL_EN in Instant calibration box
    4. Vcc power up the EVM
    5. Press Ctrl+L to program the EVM to lock to 6GHz
    6. Set INSTCAL_EN = 1 in Instant calibration box
    7. Type 5650 and then Enter in the VCO box (PLL_NUM, PLL_N and INSTCAL_PLL_NUM will be programmed automatically)
    8. Uncheck FCAL_EN in the VCO calibration box
    9. Check FCAL_EN
    10. Uncheck FCAL_EN and wait for a while (VCO will lock to 5650 MHz)
    11. Change VCO frequency, for example, type 5800 and then Enter in the VCO box (PLL_NUM, PLL_N and INSTCAL_PLL_NUM will be programmed automatically)
    12. Click Calibrate VCO button (this will write R0 once, VCO will lock to 5800 MHz)
    13. Change VCO frequency to, for example, 6200 MHz
    14. Click Calibrate VCO button (this will write R0 once, VCO will lock to 6200 MHz)

    Please note, the written SDA will be shifted to the internal register at the last (LSB) SCK rising edge.
    TICS Pro is running at around 125kHz, The delay between the last SCK rising edge and CSB is one SCK cycle. That is, the delay is around 8µs. If you use CSB as the trigger signal to the test equipment, be caution to this 8µs error.

    Hope this helps.

  • 0 in reply to Noel Fung
    Prodigy 120 points

    Hi, Noel :

    The examples illustrated above are within the same VCO, does it work for different VCO?

    For example, the frequency changes from 5800MHz to 10GHz and the procedure is totally

    the same? Just type 10000 in the VCO box and then click Calibrate VCO button.

    Regards,

    Yao-Hua

  • +1 in reply to Yao-Hua
    TI__Guru** 108480 points

    Hi Yao Hua,

    After instant calibration is done, the same frequency switching mechanism will apply to any VCO frequency and any VCO core.