AnsweredAssumed Answered

AD4360-9 jitter problem

Question asked by IngJunior on Nov 29, 2010
Latest reply on Dec 10, 2010 by icollins

Hi all,

 

i have a problem regarding the MUXOUT output of ADF4360-9.

 

I want to feed an ADC with the MUXOUT signal provided by ADF4360-9, but it seems to have a lot of jitter. My signal has a frequency of 40 MHz

 

These are my specification:

 

- VCO running frequency: 160 MHz

- External inductance: 103 nH

- Reference frequency: 20 MHz from TCXO

- R counter = 20

- N counter = 160

- DIVOUT = 2

- MUXOUT: A CNTR/2 OUT

 

I display the signal on scope using an RF cable, 50 cm long with SMA connectors. The input impedance is set at 50 Ohm, because the input impedance of ADC input clock is also set at 50 Ohm.

 

I have posted two pics, one is a detal view of the wave transition.

I had to insert a 200 Ohm resistance from MUXOUT signal to ground because otherwise i have a very ugly signal (lot of spikes, seems that without this resistance there are lot of reflections).

I can't understand if the jitter is due to a poor layout (2 layer FR4 board) or maybe my mistake using the scope (so cabling, 200 Ohm termination, etc)

 

Furthermore there is another "strange" behaviour, if i select only the A CNTR OUT i see on the scope an 80 MHz signal as expected, but it reach full amplitude (3.3 Vpp) while if i use the A CNTR/2 i reach only 600 mVpp.

 

Thanks in advance for your help.

 

Best regards

Oscar

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