LMX2594EVM: No VCO output at certain frequency band.

I tried to look at it again today, it seems that in channel divider output mode it outputs 7GHz, but when I switched to VCO output I do not see the 14GHz I expect to see. Here is my setting on TICS Pro. It was tested after a clean power cycle (LMX2594 powered on first, then the usb of the reference pro pluged in, then I go to default mode of the TICS pro, which allowed me to see 7GHz. Then I only changed channel divider to VCO. The software recommends me to turn off SEG1_EN so I did, but makes no difference.) 

This is exactly what I did and I do not see 14GHz signal.

Hi Hz,

In Step 1, if you setup TICS Pro to 14GHz output, then after programming, will you get 14GHz output?

I have success up to step 3 (where I see LD on and 7GHz signal) but at step 4 I see no RF at 14GHz

If I set frequency between 9.8GHz-12.9GHz though I can see VCO output signal..

Hi Hz,

Sorry for the confusion, what I want you to try is the following sequence:

1. open TICS Pro and change the Default Configuration to VCO output instead of divided down output. 

2. Vcc power up the EVM

3. provide a valid reference clock

4. USB Communications --> Write All Registers (it should output 7GHz, LD LED will ON. If not, uncheck - check the FCAL_EN bit to calibration the VCO again)

if you can get 14GHz output, then set the output to div/2 to get 7GHz output. After that, change it back to VCO output to see if you can get 14GHz output. I want to identify if this is a vco calibration issue or a divider issue.

Following your instruction, setting to VCO output in TICS software first then Vcc power up and write all register, I get a signal at 14.8GHz andn LD LED is not on. (The spectrum analyzer I have access to is not perfectly calibrated, but I think this is quite off from the 14GHz setpoint). Now if I toggle the FCAL_EN, the signal is gone. Now if I switch to divide-by-two output, I can get 7GHz back, but I cannot get 14.* GHz signal back anymmore until I power cycle BOTH the LMX2594 board AND the reference pro connected through USB, and it does not always work.

Hi Hz,

Your board's behavior is very weird.

Do you have the same issue if you do the same sequence for other frequencies?

are you using the Reference Pro as the 100MHz clock source to LMX2594EVM? Can you try with an external clock source?

I have checked the reference pro output and it is properly 100MHz.And it works for 10GHz signal fine, so I do not think it is the clock source. That being said, I plan to change it to a on-board crystal, but on my board the crystal is not populated, and I cannot find the proper part number. Can you suggest the proper part?