Question about AD9642

Question

Hi, 
 
 I have some questions about AD9642. Please take care of this case. 
 
 1): Question about an anti-aliasing filter for 50 ohm differential line. 
 I'll use AD4930-1 and AD9642, and I'm looking at Figure 47. in AD9642 data sheet. 
 There is the RC circuit between AD4930-1 and AD9642 and it seems to work as differential signal balance. 
 Please let me know recommended anti-aliasing filters for this differential line (50 ohm). 
 1: AD9642-170, AAF Bandwidth:75MHz 2: AD9642-250, AAF bandwidth: 100MHz 
 
 2): There are two 0.1uF caps on the VCM line shown in Figure 47. 
 The VCM line really needs two caps for ADA4930-1 and AD9642? 
 
 3): What capacitance (decoupling cap) do AVDD and DRVDD pins need? 
 
 Regards, 
 Kazu

J.Harris · Accepted Answer

Hi Kazu, 
 Let me try to answer your questions here: 
 1) I suggest looking at CN-0279 as the process will be similar when looking at interfacing the ADA4930 to the AD9642. http://www.analog.com/media/en/reference-design-documentation/reference-designs/CN0279.pdf 
 2) It is recommended to have a 0.1uF capacitor close to the VCM pin of the AD9642 as well as at the VOCM pin of the ADA4930 to provided stability for this circuit. 
 3) I would recommend following the decoupling scheme utilized on the evaluation board for optimum performance. 
 Regards, 
 Jonathan)

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Question about AD9642