Highly efficient Envelope Tracking transmitter at 3.5-GHz

Envelope Tracking (ET) transmitter is introduced at a high frequecny, 3.5-GHz. As the frequency goes up, ET system has merits because the supply modulator is frequency independent circuit. For the optimum ET operation, the Power Amplifier (PA) has been designed as an average PA to have a maximum Power Add Efficiency (PAE) at the average Vds region. An improved supply modulator without sensing resistor is designed to mitigate the power dissipation. The supply modulator is optimized to average load impedance for higher efficiency and a proper ET shaping function is applied. The proposed supply modulator shows efficiency of 83.0% near the average load impedance of 14.7 Ω. In the interlock experiment, the ET transmitter delivers an excellent PAE performance, of 35.5% at an average output power of 40 dBm. Using digital feedback predistortion (DFBPD) technique, the Relative Constellation Error (RCE) has been successfully satisfied the specification with −32.7 dB. To the best of our knowledge, the PAE of 35.5% is the state-of-the-art for 3.5-GHz transmitter.