Guidelines for two cascaded amplifers (hmc618a)

Hello everyone,

for our telecom system, we need to cascade two selected amplifers (hmc618a, 1700 - 2200 MHz tuned) in order to obtain more than 30 dB gain.

We thought to follow the datasheet reference design.

Are there some guidelines or issues we have to know to do that? Or Have you some advices?

Could the two cascaded stages oscillate?

Many thanks.

best regards,

Antonio L.

  • Hello SMcBride,

    with respect your explanation, in the gerber file of the amplifier I see the bypass capacitors far away from the power supply pins of part. I don't understand...

    Anyway, your explanation helped me to understand how to cascade the two amplifers.

    Many thanks.

    Best regards,

    Antonio L.

  • 0
    •  Analog Employees 
    on May 25, 2017 4:47 PM over 3 years ago

    Hi Antonio,

    Yes, for the HMC618A the bypass caps are out past the inductors. When I was talking about the bypass caps I was more thinking about some of our other products that don't have inductors right near the pins but instead have caps very close to the pins with just short lengths of PCB trace between cap and pin. For the HMC618A my recommendation is to follow the top layer layout shown in the gerber files as closely as possible with respect to the positions of the inductors and bypass caps for the Vdd1 and Vdd2 traces, then connect them together out past those caps (i.e. farther away from the part). Once past those caps, you should be able to connect all of the drains together (for both amps in your cascade) without causing problems.

    With most (or possibly all) of our HMC parts we generally recommend to customers that, in order to obtain performance similar to that shown on the data sheet and to increase the chances of first-pass success with their designs, they follow our EVB gerbers as closely as possible. That includes not just the traces but also the grounds and ground vias. Grounds and ground via diameter, quantity, placement, and type (PTH vs. solid/filled, etc.) can have significant effects on both the electrical and thermal aspects of circuit performance. If the thermal considerations are new to you and/or you're interested to learn more about them, here is a link to a relevant application note:

    http://www.analog.com/media/en/technical-documentation/application-notes/thermal_management_for_surface_mount_components.pdf

    If your design uses a different stack-up than our EVB then you might need to make adjustments to some of the trace widths and gaps in order to maintain the same trace impedance. Stack-up differences might also require you to increase your ground via coverage (for thicker substrates) or allow you to decrease your ground via coverage (for thinner substrates). As always with RF design, there are many factors to take into account.

    I'm glad that you found this discussion helpful. Let me know if you have more questions.

    Regards,

    SMcBride 

  • Hello,I am now also try to use HMC618A ,I plan to use it @1400MHz and  trying to find the gerber file of EVM board (1200 - 1700 MHz tuned) ,the part number is EV1HMC618ALP3,but the file provided was 1700 - 2200 MHz tuned,So could you please help me find the gerber file?

  • 0
    •  Analog Employees 
    on Dec 13, 2017 6:08 PM over 3 years ago

    Hi reeze,

    I have submitted to our website team a request that the 1200-1700 MHz eval board gerber files be uploaded to the HMC618A product page. Several days may elapse before the upload and link become active.

    In the meantime, please see the attached gerber files for EV1HMC618ALP3.

    Regards,

    SMcBride

    EV1HMC618ALP3_gerber.zip