Abstract
This paper presents a high efficiency Doherty power amplifier suitable for TV band applications. A class AB power amplifier is firstly implemented using a commercial GaN HEMT from Cree Incorporation, achieving a high power-added-efficiency of 77.78% and a 40.593 dBm output power with an associated gain of 21.65 dB. The Doherty amplifier has then been designed following the previous class AB scheme for the main amplifier and a class C scheme for the peak one. This amplifier attained a high power-added-efficiency of 81.94%, a 42.77 dBm output power, an associated gain of 21.32 dB, and an operating frequency bandwidth between 550 and 1000 MHz (58.06% fractional bandwidth) which made it suitable for TV band applications.
Highlights
The design of RF front-ends in wireless communication for cognitive radio applications has become a hot research area
The amplifier is simulated in both software, Advanced Design System (ADS) and AWR
The scattering parameters were simulated and found to be: S11 = 0.772 ∠ −157.51 ̊ S12 = 0.016 ∠ −0.034 ̊ S21 = 8.057 ∠ 85.81 ̊ S22 = 0.17 ∠ −39.773 ̊ In order to maintain maximum power transfer, we need to match the impedance of the load to that of the source, so matching circuits are designed at the input and the output of the transistor
Summary
The design of RF front-ends in wireless communication for cognitive radio applications has become a hot research area. The two power amplifiers are connected at the output through a quarter-wave transmission line to exploit the active load modulation concept performed by the peak amplifier on the main carrier one This Doherty amplifier has high linearity and efficiency across the wideband signal. Significant improvements in bandwidth have been reported recently [13]-[17], the DPA is still fundamentally bandwidth limited by the quarter wave impedance inverter needed to obtain proper load modulation This results in substantial frequency dependence at the back-off power region where the Power Amplifier (PA) is operating most of the time, and thereby narrow band performance for realistic signals. The characteristics of the designed amplifiers are investigated via Agilent Advanced Design System (ADS) software and verified using NI AWR Design Environment software
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