Hello,
I'm interested in using the MAX2021 IQ modulator/demodulator for an upcoming project. I'm currently facing challenges with impedance matching for the IF port, mainly due to my limited experience with differential lines. I'm seeking a better understanding of how the diplexer functions in their evaluation board. According to the datasheet, the impedance of the IF port is specified as 53 ohms in a differential configuration. The diplexer's role is to filter out the LO and 2xLO components. The concept is that these LO and 2xLO signals are attenuated using 100 ohm resistors. The diplexer is intended to allow the low-frequency IF signal to pass through as desired.
To facilitate easier simulation, I've attempted to convert the circuit from differential to single-ended. However, I'm puzzled as to why the LO and 2xLO signals appear to be terminated to 50 ohms (R/2).