Output power characteristics of cooled power PHEMT MMICs

Saturated power output characteristics of monolithic microwave (and mm-wave) integrated circuit (MMIC) power amplifiers incorporating double heterojunction InGaAs-channel PHEMTs (pseudomorphic high electron mobility transistors) operating at different base plate temperatures are compared. While it is generally expected that ideal PHEMTs have greater output power at lower temperatures, it is shown experimentally that this is not always the case. Indeed, the saturated output power does not necessarily follow the same trends with temperature as the corresponding small signal gain characteristics. In some cases the saturated output power is less at lower temperatures despite and increase in the corresponding small signal gain. Furthermore, the same monolithic circuit design may behave differently with temperature depending on the specific PHEMT wafer from which it was fabricated. Guidelines are presented for the selection of suitable PHEMT epitaxial material for increasing saturated output power at lower temperatures.