Hello
I have a question regarding biasing the AD9375 TX outputs using a balun DC bias. In the AD9375 System Development User Guide, this is simplified as the following configuration:
This is the recommended RF transmitter interface.
Table 175 provides matching components for TX1 at different frequency ranges. I believe it is using a balun to provide the DC bias for the 5300 to 5900MHz case.
It is not clear from this table whether L307/L308 (choke inductors) are populated or not. Please confirm that the DC bias current is provided from the balun and not from the choke inductors as follows:
Lastly, the balun specified is the TDK HHM1752A2. According to the user guide, each transmitter output (P and N) requires roughly 100mA of DC bias current:
Nowhere in the TDK HHM1752A2 datasheet can I find a specification for maximum rated DC current. Is this not a problem? Surely we need to confirm that the balun we are choosing is able to handle the rated DC bias current of 100mA per balanced input?
The reason I am asking is because I overlooked this fact when choosing a balun for a custom board. I am using a TTM X4BD40L1-5050G balun. This balun datasheet also does not specify the maximum rated DC current and I am concerned that I may be stressing the part. I am also seeing a significant signal drop across this balun, even though it's insertion loss is comparable to that of the evaluation board Mini-Circuits TCM1-83X+. I am wondering if the limited DC current handling capability of this balun is limited the transmitter maximum output drive.
Thank you in advance.
Gavin