AnsweredAssumed Answered

AD9859 evaluation board - Impedence mismatch?

Question asked by Matthew4350 on Feb 14, 2012
Latest reply on Feb 28, 2012 by Matthew4350

Dear all,

I have to design a pcb with AD9859, so I'm watching this evaluation board schematic : http://www.analog.com/static/imported-files/eval_boards/46543170023221AD9954_RevD_schem.pdf

 

I've noticed, in the first schematic sheet, an impedance mismatch from DDS's Iout and IoutB pins (21 and 22) to T2 (minicircuits transformer with impedence ratio of 1).  I think that at input port of T2 the impedence is near the sum of R9 and R8 (100 Ohm) and at T2 output port the impedence is 50 Ohm.

 

With my deisgn the maximum output frequency is near 100Mhz. Is better if I use a transformer with impedence ratio of 2 ?

Outcomes