Envelope tracking (ET) is a key technology improving efficiency of RF power amplifiers (PAs) and battery lifetime in mobile handsets. It has been commercialized since 4G LTE era, and is also being employed in 5G NR handsets. A supply modulator (SM) is a circuit generating power supplies of RF PAs for ET and average power tracking (APT) operations. Currently, the maximum channel BW and supported ET BW of 5G NR handset is 100MHz [1]–[4]. In a short time, over 100MHz BW will be necessary to support intra-band contiguous carrier aggregation cases of n77C/n78C/n79C in 3GPP standard [5]. The required instantaneous maximum output power of SM is about 10W which is calculated by the following parameters: 26dBm output power by power class 2 (PC2), 2dB loss of RF front-end module (FEM) due to complex operating band combinations (EN-DC for non-standalone mode, NE-DC, 2CA/3CA), 6dB higher instantaneous power due to peak-to-average power ratio (PAPR) at 1 resource block (RB), 1dB margin, and poor PA efficiency of around 33% (worst example) due to high carrier frequency of 5GHz at n79 band. The poor PA efficiency can be relaxed by high voltage PA design beyond 5V. In [1], a supply modulator with boosted output larger than battery voltage $(V_{BAT})$ is proposed, and the designed PA with 30% higher voltage shows 10% higher efficiency and broader BW owing to low impedance transformation ratio from $50 \Omega$ and small parasitic output capacitance of power cell. The challenge is how to design a supply modulator for 5G NR that can achieve both wide ET BW and high output voltage/power capability, while satisfying high efficiency, low receiver-band noise, short transition time, and multi-mode/standard operation.
