Part Number: LMX2820
Tool/software:
Good day
We are using an LMX2820 on a custom design, using an FPGA to handle the programming of the LMX2820.
As we have a fairly stringent lock time requirement, we have to use Instant Calibration.
Here is the procedure we followed 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
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
We are experiencing some issues with certain frequencies not locking, and it was recommended that we add step 9.5 (Run index routine).
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)
We are yet to try this, as it takes some time to open the hermetically sealed modules, but in the meantime, I would like to understand what is happening when running the indexing routine, as the registers mentioned are marked as reserved on the register map?
