LMX2594: Automatic Ramping: Limit and Start Frequency Problems

Tino Seibold

Part Number: LMX2594

Hello, I would like to generate a frequency ramp using the LMX2594 in automatic ramping mode. The phase detector frequency is 100 MHz. In CW mode, it is possible to adjust the frequency in increments smaller than 100 MHz. However, as soon as ramping is activated, the starting frequency jumps to the next lower multiple of 100 MHz. (For example: CW: 11.75 GHz -> in ramping mode, the starting frequency jumps to 11.7 GHz.) How can I set the starting frequency in smaller increments without lowering the phase detector frequency?

For testing I used a start frequency of 11700 MHz. However, the TICS Pro software calculates a value of 16777 for a lower ramp limit of 11700.1 MHz. How is this calculated, because according to the datasheet and the formula provided there, this value shouldn’t be possible at a start frequency of 11700 MHz?

3 months ago

0 Noel Fung 3 months ago

TI__Guru** 122550 points

Hi There,

Can you provide your TICS Pro configuration file?

0 Tino Seibold 3 months ago in reply to Noel Fung

Prodigy 10 points

Hello

Thanks for the reply. I created two scenarios using the TICS Pro software:

11G7_works:
In this example, I selected a starting frequency of 11.7 GHz for my ramp. First in CW mode, then in Ramp mode. The ramp is generated as intended.

11G7_works.tcs

Fullscreen 11G7_works_log.txt Download

Welcome to TICS Pro. Version -> 1.7.10.1, 17-Oct-25
Loading Device LMX2594...
Detected 1 USB2ANY interfaces
Completed loading Device LMX2594. Version = 2019-3-29
Loading configuration: E:\11G75_works.tcs
Wrote Register R112 (0x70) as 0x70 0000
Wrote Register R111 (0x6F) as 0x6F 0000
Wrote Register R110 (0x6E) as 0x6E 0400
Wrote Register R109 (0x6D) as 0x6D 0000
Wrote Register R108 (0x6C) as 0x6C 0000
Wrote Register R107 (0x6B) as 0x6B 0000
Wrote Register R106 (0x6A) as 0x6A 0003
Wrote Register R105 (0x69) as 0x69 FA01
Wrote Register R104 (0x68) as 0x68 1388
Wrote Register R103 (0x67) as 0x67 FD8A
Wrote Register R102 (0x66) as 0x66 3FFF
Wrote Register R101 (0x65) as 0x65 0010
Wrote Register R100 (0x64) as 0x64 88B8
Wrote Register R99 (0x63) as 0x63 005A
Wrote Register R98 (0x62) as 0x62 0000
Wrote Register R97 (0x61) as 0x61 8809
Wrote Register R96 (0x60) as 0x60 0000
Wrote Register R95 (0x5F) as 0x5F 0000
Wrote Register R94 (0x5E) as 0x5E 0000
Wrote Register R93 (0x5D) as 0x5D 0000
Wrote Register R92 (0x5C) as 0x5C 0000
Wrote Register R91 (0x5B) as 0x5B 0000
Wrote Register R90 (0x5A) as 0x5A 0000
Wrote Register R89 (0x59) as 0x59 0000
Wrote Register R88 (0x58) as 0x58 0000
Wrote Register R87 (0x57) as 0x57 0000
Wrote Register R86 (0x56) as 0x56 4189
Wrote Register R85 (0x55) as 0x55 0000
Wrote Register R84 (0x54) as 0x54 0000
Wrote Register R83 (0x53) as 0x53 3333
Wrote Register R82 (0x52) as 0x52 0033
Wrote Register R81 (0x51) as 0x51 0000
Wrote Register R80 (0x50) as 0x50 CCCC
Wrote Register R79 (0x4F) as 0x4F 004C
Wrote Register R78 (0x4E) as 0x4E 0275
Wrote Register R77 (0x4D) as 0x4D 0000
Wrote Register R76 (0x4C) as 0x4C 000C
Wrote Register R75 (0x4B) as 0x4B 0800
Wrote Register R74 (0x4A) as 0x4A 0000
Wrote Register R73 (0x49) as 0x49 003F
Wrote Register R72 (0x48) as 0x48 0001
Wrote Register R71 (0x47) as 0x47 0081
Wrote Register R70 (0x46) as 0x46 C350
Wrote Register R69 (0x45) as 0x45 0000
Wrote Register R68 (0x44) as 0x44 03E8
Wrote Register R67 (0x43) as 0x43 0000
Wrote Register R66 (0x42) as 0x42 01F4
Wrote Register R65 (0x41) as 0x41 0000
Wrote Register R64 (0x40) as 0x40 1388
Wrote Register R63 (0x3F) as 0x3F 0000
Wrote Register R62 (0x3E) as 0x3E 0322
Wrote Register R61 (0x3D) as 0x3D 00A8
Wrote Register R60 (0x3C) as 0x3C 03E8
Wrote Register R59 (0x3B) as 0x3B 0001
Wrote Register R58 (0x3A) as 0x3A 9001
Wrote Register R57 (0x39) as 0x39 0020
Wrote Register R56 (0x38) as 0x38 0000
Wrote Register R55 (0x37) as 0x37 0000
Wrote Register R54 (0x36) as 0x36 0000
Wrote Register R53 (0x35) as 0x35 0000
Wrote Register R52 (0x34) as 0x34 0820
Wrote Register R51 (0x33) as 0x33 0080
Wrote Register R50 (0x32) as 0x32 0000
Wrote Register R49 (0x31) as 0x31 4180
Wrote Register R48 (0x30) as 0x30 0300
Wrote Register R47 (0x2F) as 0x2F 0300
Wrote Register R46 (0x2E) as 0x2E 07FD
Wrote Register R45 (0x2D) as 0x2D C8C0
Wrote Register R44 (0x2C) as 0x2C 08A3
Wrote Register R43 (0x2B) as 0x2B 0000
Wrote Register R42 (0x2A) as 0x2A 0000
Wrote Register R41 (0x29) as 0x29 0000
Wrote Register R40 (0x28) as 0x28 0000
Wrote Register R39 (0x27) as 0x27 FFFF
Wrote Register R38 (0x26) as 0x26 FFFF
Wrote Register R37 (0x25) as 0x25 0404
Wrote Register R36 (0x24) as 0x24 0075
Wrote Register R35 (0x23) as 0x23 0004
Wrote Register R34 (0x22) as 0x22 0000
Wrote Register R33 (0x21) as 0x21 1E21
Wrote Register R32 (0x20) as 0x20 0393
Wrote Register R31 (0x1F) as 0x1F 03EC
Wrote Register R30 (0x1E) as 0x1E 318C
Wrote Register R29 (0x1D) as 0x1D 318C
Wrote Register R28 (0x1C) as 0x1C 0488
Wrote Register R27 (0x1B) as 0x1B 0002
Wrote Register R26 (0x1A) as 0x1A 0DB0
Wrote Register R25 (0x19) as 0x19 0C2B
Wrote Register R24 (0x18) as 0x18 071A
Wrote Register R23 (0x17) as 0x17 007C
Wrote Register R22 (0x16) as 0x16 0001
Wrote Register R21 (0x15) as 0x15 0401
Wrote Register R20 (0x14) as 0x14 E448
Wrote Register R19 (0x13) as 0x13 2700
Wrote Register R18 (0x12) as 0x12 0064
Wrote Register R17 (0x11) as 0x11 012E
Wrote Register R16 (0x10) as 0x10 0080
Wrote Register R15 (0xF) as 0x0F 064F
Wrote Register R14 (0xE) as 0x0E 1E70
Wrote Register R13 (0xD) as 0x0D 4000
Wrote Register R12 (0xC) as 0x0C 5001
Wrote Register R11 (0xB) as 0x0B 0018
Wrote Register R10 (0xA) as 0x0A 10D8
Wrote Register R9 (0x9) as 0x09 0604
Wrote Register R8 (0x8) as 0x08 2000
Wrote Register R7 (0x7) as 0x07 40B2
Wrote Register R6 (0x6) as 0x06 C802
Wrote Register R5 (0x5) as 0x05 00C8
Wrote Register R4 (0x4) as 0x04 0A43
Wrote Register R3 (0x3) as 0x03 0642
Wrote Register R2 (0x2) as 0x02 0500
Wrote Register R1 (0x1) as 0x01 0808
Wrote Register R0 (0x0) as 0x00 A41C
7/17/2026 8:44:00 AM Configuration is loaded successfully

11G75_works_not:
Here, I wanted to start the same ramp at 11.75 GHz. First, I set the CW frequency to 11.75 GHz, and that worked perfectly. Then I activated the ramp, and the starting frequency jumped to 11.7 GHz.

11G75_works_not.tcs

Fullscreen 11G75_works_not_log.txt Download

Welcome to TICS Pro. Version -> 1.7.10.1, 17-Oct-25 Loading Device LMX2594... Detected 1 USB2ANY interfaces Completed loading Device LMX2594. Version = 2019-3-29 Loading configuration: E:\11G75_works_not.tcs Wrote Register R112 (0x70) as 0x70 0000 Wrote Register R111 (0x6F) as 0x6F 0000 Wrote Register R110 (0x6E) as 0x6E 0400 Wrote Register R109 (0x6D) as 0x6D 0000 Wrote Register R108 (0x6C) as 0x6C 0000 Wrote Register R107 (0x6B) as 0x6B 0000 Wrote Register R106 (0x6A) as 0x6A 0003 Wrote Register R105 (0x69) as 0x69 FA01 Wrote Register R104 (0x68) as 0x68 1388 Wrote Register R103 (0x67) as 0x67 FD8A Wrote Register R102 (0x66) as 0x66 3FFF Wrote Register R101 (0x65) as 0x65 0010 Wrote Register R100 (0x64) as 0x64 88B8 Wrote Register R99 (0x63) as 0x63 005A Wrote Register R98 (0x62) as 0x62 0000 Wrote Register R97 (0x61) as 0x61 8809 Wrote Register R96 (0x60) as 0x60 0000 Wrote Register R95 (0x5F) as 0x5F 0000 Wrote Register R94 (0x5E) as 0x5E 0000 Wrote Register R93 (0x5D) as 0x5D 0000 Wrote Register R92 (0x5C) as 0x5C 0000 Wrote Register R91 (0x5B) as 0x5B 0000 Wrote Register R90 (0x5A) as 0x5A 0000 Wrote Register R89 (0x59) as 0x59 0000 Wrote Register R88 (0x58) as 0x58 0000 Wrote Register R87 (0x57) as 0x57 0000 Wrote Register R86 (0x56) as 0x56 4189 Wrote Register R85 (0x55) as 0x55 0000 Wrote Register R84 (0x54) as 0x54 0000 Wrote Register R83 (0x53) as 0x53 3333 Wrote Register R82 (0x52) as 0x52 0033 Wrote Register R81 (0x51) as 0x51 0000 Wrote Register R80 (0x50) as 0x50 CCCC Wrote Register R79 (0x4F) as 0x4F 004C Wrote Register R78 (0x4E) as 0x4E 0275 Wrote Register R77 (0x4D) as 0x4D 0000 Wrote Register R76 (0x4C) as 0x4C 000C Wrote Register R75 (0x4B) as 0x4B 0800 Wrote Register R74 (0x4A) as 0x4A 0000 Wrote Register R73 (0x49) as 0x49 003F Wrote Register R72 (0x48) as 0x48 0001 Wrote Register R71 (0x47) as 0x47 0081 Wrote Register R70 (0x46) as 0x46 C350 Wrote Register R69 (0x45) as 0x45 0000 Wrote Register R68 (0x44) as 0x44 03E8 Wrote Register R67 (0x43) as 0x43 0000 Wrote Register R66 (0x42) as 0x42 01F4 Wrote Register R65 (0x41) as 0x41 0000 Wrote Register R64 (0x40) as 0x40 1388 Wrote Register R63 (0x3F) as 0x3F 0000 Wrote Register R62 (0x3E) as 0x3E 0322 Wrote Register R61 (0x3D) as 0x3D 00A8 Wrote Register R60 (0x3C) as 0x3C 03E8 Wrote Register R59 (0x3B) as 0x3B 0001 Wrote Register R58 (0x3A) as 0x3A 9001 Wrote Register R57 (0x39) as 0x39 0020 Wrote Register R56 (0x38) as 0x38 0000 Wrote Register R55 (0x37) as 0x37 0000 Wrote Register R54 (0x36) as 0x36 0000 Wrote Register R53 (0x35) as 0x35 0000 Wrote Register R52 (0x34) as 0x34 0820 Wrote Register R51 (0x33) as 0x33 0080 Wrote Register R50 (0x32) as 0x32 0000 Wrote Register R49 (0x31) as 0x31 4180 Wrote Register R48 (0x30) as 0x30 0300 Wrote Register R47 (0x2F) as 0x2F 0300 Wrote Register R46 (0x2E) as 0x2E 07FD Wrote Register R45 (0x2D) as 0x2D C8C0 Wrote Register R44 (0x2C) as 0x2C 08A3 Wrote Register R43 (0x2B) as 0x2B 0000 Wrote Register R42 (0x2A) as 0x2A 8000 Wrote Register R41 (0x29) as 0x29 0000 Wrote Register R40 (0x28) as 0x28 0000 Wrote Register R39 (0x27) as 0x27 FFFF Wrote Register R38 (0x26) as 0x26 FFFF Wrote Register R37 (0x25) as 0x25 0404 Wrote Register R36 (0x24) as 0x24 0075 Wrote Register R35 (0x23) as 0x23 0004 Wrote Register R34 (0x22) as 0x22 0000 Wrote Register R33 (0x21) as 0x21 1E21 Wrote Register R32 (0x20) as 0x20 0393 Wrote Register R31 (0x1F) as 0x1F 03EC Wrote Register R30 (0x1E) as 0x1E 318C Wrote Register R29 (0x1D) as 0x1D 318C Wrote Register R28 (0x1C) as 0x1C 0488 Wrote Register R27 (0x1B) as 0x1B 0002 Wrote Register R26 (0x1A) as 0x1A 0DB0 Wrote Register R25 (0x19) as 0x19 0C2B Wrote Register R24 (0x18) as 0x18 071A Wrote Register R23 (0x17) as 0x17 007C Wrote Register R22 (0x16) as 0x16 0001 Wrote Register R21 (0x15) as 0x15 0401 Wrote Register R20 (0x14) as 0x14 E448 Wrote Register R19 (0x13) as 0x13 2700 Wrote Register R18 (0x12) as 0x12 0064 Wrote Register R17 (0x11) as 0x11 012E Wrote Register R16 (0x10) as 0x10 0080 Wrote Register R15 (0xF) as 0x0F 064F Wrote Register R14 (0xE) as 0x0E 1E70 Wrote Register R13 (0xD) as 0x0D 4000 Wrote Register R12 (0xC) as 0x0C 5001 Wrote Register R11 (0xB) as 0x0B 0018 Wrote Register R10 (0xA) as 0x0A 10D8 Wrote Register R9 (0x9) as 0x09 0604 Wrote Register R8 (0x8) as 0x08 2000 Wrote Register R7 (0x7) as 0x07 40B2 Wrote Register R6 (0x6) as 0x06 C802 Wrote Register R5 (0x5) as 0x05 00C8 Wrote Register R4 (0x4) as 0x04 0A43 Wrote Register R3 (0x3) as 0x03 0642 Wrote Register R2 (0x2) as 0x02 0500 Wrote Register R1 (0x1) as 0x01 0808 Wrote Register R0 (0x0) as 0x00 A41C 7/17/2026 8:43:54 AM Configuration is loaded successfully

For both cases, I’ve attached the config files, as well as log files and screenshots of the GUI.

What we actually want to do with the PLL is:

set arbitrary start frequencies for the ramp within a specific frequency band. However, the ramp’s frequency step and the timings should remain unchanged.
In general it would be possible to set the ramp Limits to the lowest and highest Frequency within our specified frequency band.
Ramp should be started on an external Trigger

Clock & timing

Clock & timing forum

LMX2594: Automatic Ramping: Limit and Start Frequency Problems