• State TI Thinks Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 2 answers
  • Subscribers 20 subscribers
  • Views 709 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LMX2492 FSK modulation

AZ1
Prodigy 100 points
Other Parts Discussed in Thread: CODELOADER

Hi,

We would like to use an external pin to FSK modulate.

Per the data sheet, this modulating pin (one of Trig_1, Trig_2, Mod) should be set to trigger TRIG_A or TRIG_B (let's assume we chose Trig_1 to activate TRIG_A), and then the device should be configured such that an FSK deviation will be activated when TRIG_A is active.

The issue that I see is that per the data sheet, TRIG_A is activated by a transition in Trig_1 (can be configured to a rising or a falling edge - let's assume rising edge).

So, the FSK deviation is applied by a rising edge in Trig_1, but I'm not sure that it is de-applied when Trig_1 goes back to zero (as I would accept from an FSK modulator).

In other words, we would like the FSK modulation to be level activated and not edge activated. Is this possible?

Thanks, 

  • 0
    TI__Expert 5370 points

    Dear AZ1,

    This is a good question and after looking in the D/S, I am not able to find a "level" control on a pin for the FSK function.

    However, the good news is that there is a work around for that. You can simple use the ramp feature to toggle between the two FSK state.

    You need 4 states to do the FSK:

    state 0: sitting at frequency "0" waiting for trig A

    state 1: go to the other frequency as fast as possible; note here that it will do it in one phase detector cycle in theory; this will obviously follow the loop dynamic .

    state 2: sitting at frequency "1" waiting for trig B

    state 3: go to the other frequency as fast as possible.

    You then set the trigger source as follow:

    This is from the ramp calculator tab in codeloader, the EVM(evaluation software) for this devices. This ramp calculator needs to be enabled as shown below. You can also set all the required registers on the bits/pins tab as well.

    Hope this helps,

    Regards, Simon.

  • 0 in reply to Simon Damphousse
    TI__Expert 5370 points
    My apology, I pasted some images here but they are gone once posted...

    What is missing really in this explanation is the trig A and B to be set to MOD Rising Edge and MOD Falling Edge respectively.

    The ramp calculator must be enabled in the options menu under "enable flex script".

    Regards, Simon.
  • 0 in reply to Simon Damphousse
    Prodigy 100 points
    Dear Simon,

    Thanks for your reply but I'm afraid that this workaround will not work for us.
    The issue is that we need the frequency shift (FSK) over a series of ramps - not over a carrier frequency.
    1. It is quite odd that the FSK feature is designed to be edge triggered and not level controlled - can you please verify that this is not simply a data sheet bug?
    2. If it is edge triggered, what will "reset" the state? i.e what will cause the FSK shift to reset, is it the next ramp?

    Thanks,
    AZ
  • 0 in reply to AZ1
    TI__Expert 5370 points
    Hello AZ,

    I went on the bench and measured. It is not edge triggered but level control so it will do what you are looking for.

    The D/S is wrong so is the evaluation software. We will fix in a near future.

    thank you for pointing this out.

    Regards, Simon.
  • 0 in reply to Simon Damphousse
    Prodigy 100 points
    Hi Simon,

    Thank you for your great support and your fast response!

    AZ