DESIGN AND DEVELOPMENT OF MULTI-STAGE L-BAND POWER AMPLIFIER USING GAN HEMT

Abstract

Power amplifier is an essential part of almost all types of communication systems and their requirements vary drastically from one application to another. In wireless communication systems and radar applications, output power, gain, efficiency and linearity are critical issues affecting the performance of these systems. The multistage power amplifier (MPA) is a key component of transmitters of microwave systems to fulfill the requirement of link budget for reliable data transmission. The focus of this thesis is to design a compact and high performance multistage power amplifier to meet the requirements of wireless communication systems and radar applications. The latest cost effective Si substrate based GaN HEMT wide bandgap semiconductor devices have been used because of their advantages in high power density and low cost. The multistage power amplifier has been developed by cascading individually designed four amplifier stages. The interstage testing points were implemented between amplifiers for their individual characterization and troubleshooting. The designing of first three stages is based on small signal technique in order to get high gain and better linearity, while final stage is designed by large signal technique to get high output power and efficiency. In multistage power amplifier the problem of oscillations due to high gain at low frequencies becomes more severe. The harmonic termination networks resonating at low frequencies are implemented in order to avoid these types of oscillations. In first phase, the individual four stages of power amplifiers are designed and characterized for class-AB operation and at a centre frequency of 1.3 GHz. First stage is designed for an output power of 16.5dBm along with 12dB gain. The second stage is designed for an output power, gain and efficiency of 34.4dBm, 15.35dB and 50 % respectively. Similarly the designed gain, output power and efficiency of third stage are 12.65dB, 41.6dBm and 53.7 % respectively. The final stage gives us gain of 13.45dB, output power of 45.5dBm and efficiency of 62.9 %. All parameters are at P1dB point. In second phase, the multistage power amplifier was designed by cascading these four amplifier stages. The output power, gain and power added efficiency at P1dB are 48.782dBm, 50.8 dB, and 48.7 % respectively. The maximum output power, gain and efficiency at saturation point (Psat) are 49.5dBm, 52 dB and 51.3% respectively. The 2nd and 3rd order harmonics during single tone measurement are -32.54 dBc and -36.88 dBc respectively, while two tones results shows that the level of third order intermodulation distortion (IMD3) is about -33 dBc.