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LMX2820: Using instant Calibration unable to output 5.65 GHz

Rou-Yin Huang
Prodigy 30 points
Part Number: LMX2820


Tool/software:

When I use Instant Calibration to output a frequency of 5.65 GHz for the first time, it outputs 5.6 GHz instead, and the LMX2820 fails to lock when set to output 5.65 GHz.

Additionally, when using Instant Calibration for frequencies above 13 GHz, some frequencies cannot be locked.

Could you please advise on a solution?

  • 0
    TI__Guru** 109810 points

    HI Rou Yin,

    What is your fpd and PLL_DEN setting?

    BTW, please follow below programming sequence for InstCal. 

    Initialization register setting
    1. Set DBLBUF_PLL_EN, DBLBUF_CHDIV_EN, DBLBUF_OUTBUF_EN, DBLBUF_OUTMUX_EN = 1
    2. Set DBLR_CAL_EN = 0; INSTCAL_SKIP_ACAL = 0
    3. If VCO doubler is required, set INSTCAL_DBLR_EN = 1, otherwise set this bit to 0
    4. Set INSTCAL_DLY = T x fosc (in MHz) / 2^CAL_CLK_DIV, where T = 2.5 x CBIASVCO / 0.47µF. CBIASVCO is the bypass capacitor at pin 3
    5. Configure other registers to lock to 5.65GHz without any calibration assist
    6. Set INSTCAL_PLL_NUM = 2^32 x (PLL_NUM / PLL_DEN)
    Programming
    7. Vcc power up LMX2820
    8. Program all the registers, LMX2820 should lock to 5.65GHz
    InstCal calibration
    9. Program INSTCAL_EN = 1
    9.5 run Index routine
    10. Program R0 (with FCAL = 1), calibration will begin
    11. Wait 100ms
    12. Program R0 (with FCAL = 0) to complete the calibration
    13. If LD pin did not turn HIGH, program RESET = 1 to reset LMX2820. After LMX2820 is reset, repeat Step 8 to 12
    Changing VCO frequency
    14. Program INSTCAL_PLL_NUM, PLL_N, PLL_NUM and PLL_DEN (if their value have change)
    15. Program R0 (with FCAL = 0) to change VCO frequency

    9.5 Index routine
    1. Program R106[10] = 1 (0X6A 0400)
    2. Program R107[5:0] = 0 (0x6B 0000)
    3. Program R108 = 0 (0x6C 0000)
    4. Program R109 = 0 (0x6D 0000)
    5. Program R106[9:0] = 514 (0x6A 0602)
    6. Program R106[11] = 1 (0x6A 0E02)
    7. Program R106[11] = 0 (0x6A 0602)
    8. Repeat step 5 to 7 for R106[9:0] = 515 to 519
    9. Program R106[10] = 0 (0x6A 0000)