Hello

We need Sweep Frequency 20MHz to 40MHz.

Please help me out how to calculate DFTW and DFRRW

if we assume DFRRW is 65535

Thanks

Hello

We need Sweep Frequency 20MHz to 40MHz.

Please help me out how to calculate DFTW and DFRRW

if we assume DFRRW is 65535

Thanks

Hi,

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.

Hi

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.

Thanks

- 1 person found this helpful
Hi,

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 DFRRW

if we assume DFRRW is 65535

Thanks

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

Thanks

- 1 person found this helpful
Hi,

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.

Hi

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

Result:

There is no sweep or output

i dont know where i am wrong kindly help me out

Thanks

Hi,

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.