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.

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  • 0
    •  Analog Employees 
    on Apr 5, 2018 4:26 PM over 3 years ago

    Hi Antonio,

    The same way you would measure Gain(S21) of your setup but this time check S12.

    When I say your setup, that means including two amps along with biasing circuitry.

    Note: HMC618A has reverse isolation more than 30dB than means that two amps cascaded together ideally would need to have Reverse Isolation more than 60dB. So if you measure huge reverse isolation degradation of your setup that means that there is some feedback in your setup so Bias Circuitry might be culprit. 

    Bear in mind that potential instability problems may occur for frequencies even out of your band(1.7G-2.2G) therefore stability has to be verified for all freqs for which Amplifier have Gain.

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  • 0
    •  Analog Employees 
    on Apr 5, 2018 4:26 PM over 3 years ago

    Hi Antonio,

    The same way you would measure Gain(S21) of your setup but this time check S12.

    When I say your setup, that means including two amps along with biasing circuitry.

    Note: HMC618A has reverse isolation more than 30dB than means that two amps cascaded together ideally would need to have Reverse Isolation more than 60dB. So if you measure huge reverse isolation degradation of your setup that means that there is some feedback in your setup so Bias Circuitry might be culprit. 

    Bear in mind that potential instability problems may occur for frequencies even out of your band(1.7G-2.2G) therefore stability has to be verified for all freqs for which Amplifier have Gain.

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