RF LDMOS BASED PUSH-PULL POWER AMPLIFIER

Abstract

The aim of work presented in this dissertation is to realize a Push-Pull Class B amplifier with high power, high efficiency performance. The key component for the push-pull is Balun (Balanced to Unbalanced), which converts between balanced and unbalanced signals at input and output respectively. A Marchand Balun was realized over a frequency range of 0.3 GHz to 1 GHz. A good magnitude and phase response was realized for the same. A single ended Class B amplifier was realized at 400 MHz frequency. Results obtained for the same showed good power gain characteristics, and output power delivered reached close to the rating of the transistor (16 W) with an input power less than 1 W. A Push-Pull Class B amplifier was realized using the realized Balun and single ended Class B amplifier circuits. Maximum possible output power that can be delivered from this configuration is 31.11 W (limited by power rating of the transistor used). Power added efficiency of 72.89 % and Drain efficiency of 76.8 % was obtained from the configuration. For the push-pull amplifier, the second harmonics were very well suppressed. Output power of second harmonic (at 800 MHz), which lies in the bandwidth of Balun was observed. Results showed that the second harmonic power at the single transistor was suppressed by 17 dBm at the output of push-pull amplifier for the 3 dB gain compression point for input.