HMC985ALP4KE_DC blocking capacitor of RF In/Out port

Question

Dear Team, 
 I think that HMC985ALP4KE needs DC blocking capacitors at the RF In/Out port. 
 But I can't the DC blocking capactor value(refer to the EVAL-CN0390-Schematic-revB.pdf). 
 I want to get the your advice. 
 Thanks. 
 Best regards, 
 Josh

stevereine · Accepted Answer

Hi Josh, 
 I designed the CN0390 board. You are correct, the HMC985A does need a dc blocking cap on both the input and outputs. However, on the CN0390 board the HMC985A output is driving the HMC635 RF amplifier, which does have dc blocking on its inputs, so no need to add caps at the HMC985A outputs. 
 I did not add a dc blocking cap to the HMC985A input because I was concerned that the cap I chose would affect the bandwidth of the circuit. My intention was to create the CN0390 board with as wide a bandwidth as possible, and the customer could add a dc blocking cap that would work in their bandwidth of interest. 
 Let me know if this makes sense to you, or if there is more I can do to help. Very happy that you are interested in using this board, 
 Steve)

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HMC985ALP4KE_DC blocking capacitor of RF In/Out port