We need Sweep Frequency 20MHz to 40MHz.
Please help me out how to calculate DFTW and DFRRW
if we assume DFRRW is 65535
you just need to use the formula (this can be found in page 18 of datasheet):
It is you who need to define either t (time duration of the sweep) or DFTW (the frequency increment).
So say you have DFTW = 1MHz, SYSCLK of 1GHz, DFRRW of 65535, the time duration of the sweep would be 22.52ms.
t is needed because the sweep operation in AD9858 does not have automatic stop-at-a-frequency.
Thank you so much for your Reply.
I don't understand about this formula
IF we have Final Frequency 40 MHz and Start Frequency is 20 MHz and SYSCLK is 1 GHz
how to calculate DFTW and DFRRW ?
As you have used above DFTW = 1 MHz why you used 1 MHz why you not used 10 MHz. .
kindly calculate this formula as i give you start and final Frequencies.
In my calculation, I have assumed DFTW to be 1MHz because you haven't define it in your post:
nome wrote: Hello We need Sweep Frequency 20MHz to 40MHz.Please help me out how to calculate DFTW and DFRRWif we assume DFRRW is 65535Thanks
So, if you want a 10MHz DFTW, you just plug in the known values (DFRRW=65535, Fsysclk, start freq and final freq) and you can solve for the unknown which is t (the time duration of sweep).
If your system clock Fsysclk is 1GHz, using the formula, t = 2.25ms.
Thank you so much
your instruction is useful for me Thanks again
i can calculate t , Delta F and also Delta t results are good ...
we have FPGA Based Board with AD9858 .i have checked Single Tone mode its working fine i can control complete band from HDL
Now i am going to use Sweep mode .
i want share my steps below.
1.Manage CFR ,DFTW DFRRW Addresses. then first
2.Start frequency should be in FTW 0
3.Manage Data and Address for DFTW and DFRRW Registers as per formula.
4.Auto CLR Freq Accum bit should be high when we need to stop Sweep ..
please Suggest me where i am wrong
sorry for my Bed English
If you need to stop the frequency, you need to write a 0 on the DFRRW register.
So after setting the control registers, start freq, final freq, dftw and dfrrw, you need to program that after time t is achieved, you write 0 to DFRRW register.
setting the auto clear freq accum bit returns the sweep to the start freq.
In Sweep mode first we assigned CFR Address like
0x00 [7:0] 01101000
0x01 [15:8] 10000000
0x02 [23:16] 10000000 also Explain me about Load Delta Frequency Timer ????this bit be high or low in sweep mode
then loaded start frequency into FTW0
after we assign DFTW ....suppose we load 1 MHz DFTW 0004294968 Decimal
then we loaded DFRRW 65635 ....524.280uS
There is no sweep or output
i dont know where i am wrong kindly help me out
After writing at the registers, have you sent an FUD? Please see Figure 34 for the timing diagram.
Retrieving data ...