HMC8500 : strong compression of positive half-wave

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

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

Thank you, Jim, for the hints.

But its only the positive half-wave which is heavily compressed. The negative follows the gain of the datasheet.

Example below : @330 MHz,  7dBm / input -> app. 25dBm / output

- Positive half-wave = 4.8Vp

- Negative half-wave = 6.3Vp

At low power levels, all looks fine.

But if I go to higher power levels, this asymmetry gets worse and worse.

Picture below  is 2V / DIV & 1ns / DIV. Scope BW = 1.3 GHz

  Vdd = 28V, Vgg = -2.3V, load = 50Ohm

  Iddq = 100mA (RF off)

  Idd = 120 mA (RF ON)

Best regards,

Marco

Hi Marco,

                 It is caused by the device starting to compress. The asymmetry is just how this device behaves.

Regards,

Jim B