Volume 11 Issue 2 ( June )

Energy-efficient power amplifiers (PAs) that preserve battery life for extended periods of time, without sacrificing linearity are becoming increasingly important for mobile devices. The supply modulator in the envelope tracking (ET) design affects the efficiency enhancement in radio frequency (RF) PAs. This paper presents design of a comparator-based supply modulator that dynamically controls the supply voltage required to drive the PA. A preamplifier has been designed to amplify the RF input signal and an envelope detector tracks the amplified signal within the comparator’s swing of 0 - 3.3 V. A single-bit comparator has been designed that works at 2.1 GHz frequency with a minimal rise-time delay of 0.2 ns and it is cascaded to operate as an 8-bit comparator. The multilevel supply modulator receives the input from the 8-bit comparator. This determines the amount of current flow to the PA by limiting current flow through the transistors that are turned OFF by the comparator. Hence the comparator based envelope tracking system is aimed at designing the ET circuit and improving the power added efficiency to approximately 45% Moreover the ET circuit does not comprise of bulky components like the inductors, thus expected to consume lesser chip area.

Keywords: Radio Frequency Power Amplifier; 5G mobile communication; 130nm CMOS; eight- bit comparator; envelope tracking; multilevel supply-modulator; linearity; efficiency