Ji-Seon Paek

2.7 A hybrid supply modulator with 10dB ET operation dynamic range achieving a PAE of 42.6% at 27.0dBm PA output power

Envelope tracking (ET) prolongs the battery life by modulating the supply of a power amplifier (PA) according to the signal envelope. With this emerging technology, the PA efficiency is greatly improved, whereas the supply modulator (SM) itself needs to provide efficient and accurate envelope tracking for the overall performance of the SM-PA combined system (PA module). The ET technique, meanwhile, has seen limited use in high-power transmission due to the reduced SM efficiency for low output power originating from the linear stage in hybrid structures [1].

20.7 An RF-PA supply modulator achieving 83% efficiency and −136dBm/Hz noise for LTE-40MHz and GSM 35dBm applications

Recently, supply modulation (SM), instead of a constant supply voltage, has raised interest in enhancing the overall SM-PA efficiency. In the average-power-tracking (APT) method, a buck converter simply generates stair-case voltages for a PA according to its required output-power level. In a more advanced envelope-tracking (ET) method, typically a hybrid structure of a low-loss but slow buck converter and a high-speed linear amplifier is used to track the fast-changing signal envelope with its efficiency performance becoming important for high peak-to-average power-ratio (PAPR) signals, like LTE [1-4]. The challenge is how to design an SM-IC that can achieve both a large-envelope-tracking bandwidth and good system-power efficiency, while achieving low output noise to minimize receive-band sensitivity degradation.

Envelope Modulator for 1.5-W 10-MHz LTE PA Without AC Coupling Capacitor Achieving 86.5% Peak Efficiency

An envelope modulator (EM) is presented to increase the efficiency of an RF power amplifier. In order to supply an output voltage higher than the input voltage while providing low-frequency power in the EM, a single-inductor dual-output (SIDO) converter is introduced. By employing the SIDO converter, the EM does not require an additional boost converter. In addition, a high-frequency converter (HFC) with a wide-bandwidth capability is also proposed. These two converters, the SIDO converter and the HFC, are combined in parallel without an ac coupling capacitor by employing a low-frequency current-balancing technique. The chip is implemented in a 0.18-μm CMOS process and achieves 86.5% peak efficiency while tracking a 10-MHz long-term evolution envelope signal.

A − 137 dBm/Hz Noise, 82% Efficiency AC-Coupled Hybrid Supply Modulator With Integrated Buck-Boost Converter

This paper presents a hybrid supply modulator (SM) with a comprehensive analysis of receiver (RX) band noise in an envelope tracking power amplifier (ET-PA). The designed SM supports both ET mode and average power tracking (APT) mode depending on the PA output power level. In the APT mode, an integrated buck-boost (BB) converter with hysteretic control generates dc supply voltage and its average switching frequency ranges from 1 to 2 MHz. In the ET mode, the bandwidth of SM is determined by a linear amplifier, which has about 30 MHz of signal bandwidth. To improve the ET efficiency, an ac coupling capacitor, with an adaptive offset control, and scaled linear supply are used. The scaled linear supply is provided by the BB converter. To lower the output noise of the SM, a parallel class-AB output buffer and resonance frequency tuning schemes are applied in this paper. For long term evolution 10 MHz with quadrature phase shift keying modulation and 5.8 dB peak-to-average power ratio, the designed SM achieves 82% efficiency at 800 mW output power with a fixed 8 Ω resistor. Adapting the proposed SM to a PA, a 10 dB ET operation dynamic range is achieved while achieving a power added efficiency of 42.6% at 27 dBm PA output power. The measured SM output noise is -137 dBm/Hz at 95 MHz offset with the PA load, and the PA RX band noise is -124 dBm/Hz, which is dominated by the stand-alone PA itself. The chip is implemented with a 130 nm CMOS process and the die size is 5.0 mm2.

86.55% Peak efficiency envelope modulator for 1.5W 10MHz LTE PA without AC coupling capacitor

For achieving boost capability and wideband with high efficiency in Envelope Modulator (EM), a newly proposed topology is introduced in this paper. The proposed EM consists of two converters: one is Low Frequency Converter (LFC) with Single Inductor Dual Output (SIDO) and the other is High Frequency Converter (HFC) with wideband capability. The two converters are combined directly in parallel without AC coupling capacitor by employing Low Frequency Current Balancing (LFCB) technique. The chip is implemented in 0.18μm CMOS process achieving 86.55% peak efficiency while tracking a 10MHz LTE envelope signal.