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Reduced gain in HMC998APM5E controlled by HMC980

Category: Hardware

Hi there,

I'm using the HMC998 with HMC980 in my circuit that follows roughly the same circuit as their evaluation boards. I'm running the amp from 15V VDD and setting the R sense to 300R for the 500mA operation of the amp. However, when measuring the gain, I'm not getting the full gain/P1dbm out of the amp, what could be wrong? 

Although I have set the resistor divider in the controller for 9V5, I'm reading 8V5 at the gate voltage of the amp. I've attached my amp circuit diagram below (for operation at 12 GHz). Any suggestions would be appreciated! 

Cheers,

Amin

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  • Hi Amin,

    I would suggest operating this circuit at ~600-650mA. When using these ABC's the suggested current for operation is what it would be at P1dB of the amplifier.. I've attached the link to the updated calculator for selecting discrete components in case you haven't been using it.

    hmc980 (1).zip

    Thanks,

    DanO

  • Hi Dan, thanks for your reply. Using the calculator, entering 15V for Vdrain and 650mA for Idrain, the suggested Rsense is 230R. I can certainly try this out, assuming this is not going to damage the PA! But hopefully, it will get me close to the maximum P1dBm/Gain. 

    Cheers,

    Amin

  • I've tried the new Rsense now (240R), the current draw of the PA has increased as expected but still no luck in getting the expected gain / p1dbm from the PA. All the voltages read ok and the PA does get warm so no idea what's happening! 

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  • I've tried the new Rsense now (240R), the current draw of the PA has increased as expected but still no luck in getting the expected gain / p1dbm from the PA. All the voltages read ok and the PA does get warm so no idea what's happening! 

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