DC block between HMC519 and HMC1019

Question

Hi, 
 Like a lot of people it seems, I have some doubt with my design when I read in datasheets " Blocking capacitors are required if RF line potential is not equal to 0V .". 
 I have 2 configurations in my design for which I assume I don't need DC block capacitors, but I would appreciate a confirmation: 
 1. I use the following chain: HMC519LC4+HMC1019ALP4E+HMC498LC4 
 HMC519 and HMC498 are AC coupled on RF ports, but the HMC1019 datasheet says " Blocking capacitors are required if RF line potential is not equal to 0V. " Can you confirm in this case that I don't need to use DC block capacitor between the HMC519 and the HMC1019, and between the HMC1019 and the HMC498 ? 
 2. I use this second chaine too: DC block+Attenuator pad+HMC547ALP3E+HMC1019ALP4E+DC block 
 The datasheets of both HMC547 and HMC1019 say " Blocking capacitors are required if RF line potential is not equal to 0V. " Can you confirm in this case that I don't need to use DC block capacitors (neither between the attenuator pad and the HMC547, nor between the HMC547 and the HMC1019) ? 
 More generally, for a RF port which is specified " Blocking capacitors are required if RF line potential is not equal to 0V. ", is it correct to approximate it, from a DC point of view, as a self connected to GND ? 
 Thanks in advance for your help, and best regards, 
 Antoine

SMcBride · Accepted Answer

Hi Antoine,

Regarding your scenario #1 from your email below:
 I support the HMC519LC4 and have in the past supported the HMC498LC4, so I can answer definitively for those two products. The HMC519LC4 and HMC498LC4 both have RFIN and RFOUT ports that are DC blocked on-chip. Their data sheets state that DC blocks (or AC coupling caps) are present, and I verified those statements are true by reviewing the die layout. Considering the HMC519LC4 and HMC498LC4 provide DC blocks, directly interfacing them with the HMC1019ALP4E as shown in your scenario #1 below will not require additional, external DC blocking (regardless of whether or not the HMC1019ALP4E has internal DC blocking).

Regarding your scenario #2 from your email below:
 The HMC1019A and HMC547ALP3E are not products that I support. They are supported by two different groups, so I would need to forward your question to those groups in order to obtain definitive answers beyond what I can see on their data sheets. The HMC1019ALP4E data sheet states that its RF1 and RF2 ports are DC coupled and that (external) blocking capacitors are required if the RF line potential is not equal to 0V. The HMC547ALP3E data sheet states that it operates down to DC, which necessarily means that its RF ports are DC coupled. The Pin Descriptions table says that (external) blocking caps are required if the RF line potential is not equal to 0V. The data sheet for the Mini-Circuits YAT-6+ shows that it operates to DC, which necessarily means that its RF ports are DC coupled. Considering the above, you will need to provide DC blocks between all of the following: YAT-6+, HMC547ALP3E, and HMC1019ALP4E.

Regards,
 SMcBride)

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DC block between HMC519 and HMC1019