HMC8500 : strong compression of positive half-wave

Question

I am testing the HMC8500 AD eval board with CW sinewave at 330 MHz, Vdd = 28V, Vgg = -2.3V, Iddq = 100mA, load = 50Ohm : 
 
 - -4dBm / input -> 15.5dBm / output : slight compression of positive half wave 
 - 2dBm / input -> 21dBm / output : significant compression of positive half wave 
 - 7dBm / input -> app. 25dBm / output : very strong compression of positive half wave 
 
 I was expecting a nice sinewave output - especially at these low power levels. 
 Where is my misunderstanding of this device ? 
 I.e., can I not achieve symmetric output voltages at Pout >> 20 dBm ?

ADIApproved · Accepted Answer

Hi Benlumentum, 
 HMC8500 is fabricated using Gallium Nitride, (GaN). GaN devices exhibit a soft compression characteristic. So, the gain rolls off earlier than GaAs devices do. Refer to Figures 29 thru 33 in the HMC8500PM5E datasheet. This soft gain compression is shown. 
 
 Regards, 
 Jim B)

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HMC8500 : strong compression of positive half-wave