want clarity on the impedance of the RF and LO inputs.

Question

I want to drive a signal based on an LVDS oscillator into the LO of this mixer. The data sheet says 50 ohms differential in text and when it talks about the inputs it says they are 50 ohms. The eval board seems to have traces for 50 ohms to ground. So, is this 100 ohms differential (so I can drive directly into the differential input) or is it 50 ohms and I need a 2:1 impedance matching transformer?

enash · Accepted Answer

The LO input port has a differential input impedance of 50 ohms. The evaluation board was designed to offer various LO configuration options (differential input, single external input to balun to differential input, Single-ended input with ac-coupling capacitors). This presents challenges for the pcb trace design, that is, whether and which traces should be 25 ohms or 50 ohms. The board was designed with 50 ohm traces. That suits single ended drive through an ac-coupling capacitor with LOIN ac-coupled to ground. 
 If you want to drive the LO port differentially with and LVDS signal which is differential and has a characteristic impedance of 100 ohms, then you would ideally have two side-by-side 50 ohm traces, a 2:1 balun, and two 25 ohm traces into LOIN/LOIP. A simpler approach would be to just take one side of the LVDS signal, ac-couple it into LOIP and then ac-couple LOIN to ground. In this case, all of your traces would be 50 ohms.)

SLA Status	Assignee	Support Status
SLA Closed. Met after 70 hours	Namratha All	Open

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want clarity on the impedance of the RF and LO inputs.

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