Variable output, high efficiency-low distortion S-band power amplifiers and their performances under single tone and noise power excitations

Abstract

A family of one stage, high efficiency-low distortion variable output power MIC amplifiers for narrow band applications at S-band was developed. The amplifiers utilize 0.5pm gatelength PsHEMT devices with 4.Xmm to 19 2mm peripheries. High efficiency (>60%) is maintained under CW operation at 2.45GHz over 12dB of input range by varying Vds between 2 and 8V. At 2.45GHz, amplifiers with 19 2mm devices biased at Vds=8V, provide 12W of single tone power at 62% PAE with I 3dB gain (1 dBc) and 36.5dBm noise power at NPR-17dB (40MHz wide noise with 700RHz notch) with 4.3% efficiency. INTRODLKX'IONNon distorting power amplifiers which operate at high efficiency over a range of input powers are useful for communication applications i n which t h e conservation of prime power is important. A family of such amplifiers where high efficiency. linear operation is maintained over a 12dB range of input powers has been developed for narrow band (200-300MHz) applications at S band. The amplifiers use 0.5pm long g a k s PsHEMT devices and the high efficiency is achieved by varying the drain voltages of the devices over the range of 2 -8 Volts 'The family of amplifiers comprises single stage, single device, hybrid MIC amplifiers with device peripheries in the range of 4.8mm to 19.2". Operating at Vds = 8V, the family of amplifiers delivers 3W to W2W of output power with single tone excitation. The amplifiers operate at a minimum of 60% power added efficiency and provide 13 -15 dR of associated gain with le5s than IdB o f gain conipression.PsHEMT DEVICES 'The characteristics of our PsHEMT devices make them ideal choices for usage as high efficiency, linear power amplifiers with variable output capabilities. The Cti~577-4/95/0000-0441F01 .oO Cr' 1995 IEEE high gain at low drain currents and the sham pinchoff i large-drain voltages enable the devices to operate very efficiently over very large portion of their I-V characteristics. Our amplifiers maintain their linearity, bandwidth and high efficiency when their drain voltages are reduced to as low a value as 2V. This is accomplished without retuning the amplifiers at each drain voltage -the amplifiers are fixed tuned.Amplifiers with comparable performance have not been previously demonstrated with any solid state devices.The PsHEMT devices have been described in recent publications ( I , 2 ) . The open channel currents are 500-6OOmA/mm, the pinch-offs -0.6 to -0.8V and the gatedrain breakdowns 14-20V. The gates are 0.5pm long and have 300pm unit peripheries. The gate to gate spacings are 40pm and the source to drain 3pm. The gates are connected to a bus bar running along the devices. Gate and source pads are interleaved on the input side. The sources are airbridged over the gate bar and each group of four is connected to a pad which is grounded through a via. A bonding pad is provided for each group of eight gates. The drains are connected on the output side to a wide bar suitable for bonding. The devices are lOOpm thick. AMPLIFIERS DESIGNThe amplifiers are designed to provide the devic...

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