ADCLK846 and some AD9851

Hello

Actually I have some AD9851 DDS ICs in my circuit like the below:

so I need a CMOS clock distributor to feed them simultaneously.

the supply voltage for AD9851 is +5V bcoz in this condition the maximum output frequency can be achieved as following:

as you see in the above the the minimum level to have logic 1 is 3.5V. the problem it is.

is there such clock distributor for such application? ADCLK846 is a good choice? I think I should place a resistive network to meet the required condition.

my friends used this circuit to use some AD9851: (I think it's not a good design bcoz we should isolate the clocks)

Best Regards



tagged
[edited by: JValeriani at 1:53 PM (GMT 0) on 14 Oct 2019]
  • 0
    •  Analog Employees 
    on Oct 14, 2019 1:43 PM over 1 year ago

    HI,

    You want to supply the AD9851 at 5V. This means you need to ensure the ref clock meets the 5V logic thresholds: 3.5V min for HIGH level and 1.5V max for LOW level.
    The ADCLK846 is a good choice if you look at the timing characteristics (compared with the flip flops), but it is supplied at 1.8V and the output logic levels are 1.7V min for HIGH and 0.1V max for low. So it is not compatible with the 5V AD9851 inputs. You would have to use voltage translators after it.

    Petre

  • I've never seen such  a solution with voltage translator... AD9851 clock interface has not been designed well. just look at AD9744 DAC... one of the worst Clock interface... not easy compatible with other devices... when you have multiple ICs in a circuit, these ICs are big problem. even ADI doesn't upgrade these ICs and only wants to produce some new ICs... so the new ICs will have a different interface completely and you should learn a new DAC again!