Linearity improvement of multi-Watts 24-28 V InGaP/GaAs HBT by low frequency low source impedance matching

InGaP/GaAs HBT running at 24-28 V operation voltage has demonstrated over 20 W output power in the standard MMIC format with efficiency over 60%. On-chip power combining of multiple HBT building-blocks successfully delivered the power transistor with multi-tens watt output power without any undesired spur. Two-tone linearity and other modulation signal were used to characterize the linearity of the HBT power transistor. By properly matching the HBT at the RF frequency, as well as the low frequency source impedance, linearity is clearly improved. WCDMA signal with ACLR1=-45 dBc is achieved with only 8 dB backoff, as compared with the WCDMA test method 1 of 9.8 dB peak-to-average ratio; the efficiency reaches 20%. This effort clearly demonstrated the potential of InGaP/GaAs HBT in the high power, high voltage operation.