# AD9789 setup of I and fBAUD?

Question asked by stistevenlee@hotmail.com on Oct 19, 2017

Hi:

I have a setup question of fBAUD rate and Interpolation,

We provide a source sync interface to AD9789,

One channel, BW=16, DW=16, and F=complex mode = 2

When channel prioritization = 0 and follow page 47.(2) formula at N to 1,

Mode: Channelizer Mode

fBAUD = 4 x 48/7 = 27.45MHz,

I(Interpolation) = 8.

page 47.(2) formula:

cyclesINTERFACE = N x F x DW/BW

F=2, DW=16, BW=16, N = 1 (Channel) thus "channel prioritization = 0"

cyclesINTERFACE= 1 x 2 x 16 / 16 = 2

page 42. formaula:

P/Q=0.58, I=8, DCO_DIV(N)=1

fDAC = I x P/Q x 16 x fBAUD

fDAC = 8 x 0.58 x 16 x 27.45 =2037.89MHz

fDCO = fDAC / 16 * N (N = DCO_DIV here from SPEC)

fDCO = 2037.89/16*1 = 127.36MHz

page 47.(1) formaula:

cyclesAVAIL = floor{fDCO/maxfBAUD} = 127.36/27.45 = 4.639 (Take an integer = 5)

page 52(1) formaula:

cyclesAVAIL >= cyclesINTERFACE + LTNCY[2:0] + 2

According to the formula:

cyclesAVAIL = 5, cyclesINTERFACE = 2, LTNCY[2:0] = 1

-> 5 >= 2 + 1 + 2

Based on the above settings, and AD9789 file description fBAUD = fFS,

1. fBAUD = fFS = 4*48M/7 = 27.45MHz, why we can not detect sync the fFS equal to 27.45MHz, it's just between 8.06M~9.02M of fFS from waveform?

2. If i set this on channel prioritization = 0, how much frequency of fFs interval should be?

3. Page47 Design Example said: the selected fDCO should be at least 8 × fFS. Is it must be to do?

4. We used as below table 96. It's wrote support "Channel prioritization = 1" only,

Whether it can not be set to "Channel prioritization = 0"??

BRs

Steven