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How to use TX data in ADF4159

Hi , 

I am trying to use  TX data pulse  to trigger the PLL to generate ramp. As per the design of my application , I need to trigger each and every chirp(ramp) and also change the frequency when needed. 

It would of great help if some one can answer my doubts:

1. The INITIALIZATION SEQUENCE register loading method given in the data sheet tells that the sequence after powering up the device is r7-r6(STEP SEL = 0)-r6(STEP SEL = 1)-r5(DEV SEL = 0)-r5(DEV SEL = 1)-r4(DEV SEL = 0)-r4(DEV SEL = 1)-r3-r2-r1-r0.  But in my application i am directly giving the   ramping values to PLL  in sequence r7-r6-r5-r4-r3-r2-r1-r0 and its locking successfully. And for change in frequency i am loading all the 8 registers in sequence  r7-r6-r5-r4-r3-r2-r1-r0. Is the correct way to change the frequency given my ramp configuration is same for all frequencies and the changing parameters i found is R2 and R0 register.

NOTE:  all the questions asked below are using the TX data pulse as trigger for generation of the ramp. Also I have been able to lock the PLL using TX ramp clk in CLK DIV mode.

2. So initially i will load all the 8 register values (in the order R7 - R0)based on the output desired by me. Then the PLL awaits for TX pulse to generate a chirp(ramp). So my doubt is for the next ramp which will be of the same frequency do i need to load any registers before TX data or i just need to toggle TX data when n where i need a chirp.

3. And does each TX data pulse trigger only one chirp ( sawtooth ramp waveform). 

4. Now to change frequency is it necessary to load all the 8 register again or does register R0 and R2 sufficient to change the frequency given the type of ramp I need is same.

Thanks and Regards,


  • 1) Since you are using a sawtooth ramp you do not strictly need to program the down ramp (i.e. only step sel = 0 and dev sel = 0 do anything in the sawtooth modes). If you wanted to use a triangle ramp you would need to follow the initialisation guidelines in the datasheet otherwise the down ramp would not be programmed correctly.

    If you only want to change the start and stop frequency of your ramp and keep the ramp profile the same then you can update the frequency by only writing reg0 and reg1 to update the int/frac words. You do not necessarily need to write the full init sequence every time.

    2) If you have PLL setup for TxData triggering and ramp mode set to single sawtooth burst (reg3[11:10] = b10) then you will get one ramp for every pulse on TxData. No extra writes required in between. 

    3) See point 2. Yes one single ramp per TxData pulse as long as reg3[11:10] = b10. For the continuous ramp settings, after TxData pulse starts a ramp it will continue ramping until a write to reg0 is made to turn ramps off.

    4) You should only need to write reg1 and reg0 to change your frequency of operation (assuming that you only want to shift the ramping frequency and all other ramp settings will remain the same).

  • Hi Aandrews,

    Thanks for the quick response. I shall implement the same and update you.