A 2.7W AC-coupled hybrid supply modulator achieving 200MHz envelope-tracking bandwidth for 5G new radio power amplifier

Modern wireless communication system especially the 5G needs much higher throughput, which requires wide channel bandwidth and high peak-to-average power ratio (PAPR) envelope. This kind of signal seriously deteriorates the efficiency of power amplifier (PA). Envelope tracking (ET) is an effective way to maximize the efficiency of PA which should be operated in the power back-off region for linearity. It has been commercialized since 4G LTE era and is also being employed in 5G NR handsets [1]. The prior art envelope tracking supply modulators (ETSM) rely on the hybrid architecture, i.e. a wideband linear amplifier (LA) and a low-loss switching power modulator (SPM), to improve power efficiency. The AC-coupled hybrid ETSM [1], 3, [4] filters the DC envelope signal, leaving only the AC component to the LA. Hence, the supply voltage of the LA can be lower than the peak envelope voltage for higher efficiency. On the other hand, the bandwidth of the ETSMs is often limited to 40MHz-130MHz [1]–[4]. An even higher bandwidth to accommodate 5G New Radio (NR) remains a bottleneck because of the large output capacitor introduced by PA. A recently reported ETSM [5] achieves 200MHz bandwidth but with a rather ideal resistive load of $5 \Omega$. In this paper, the ETSM is loaded with a more realistic PA model of $4 \Omega //600$ pF. By utilizing diverse circuit techniques, the proposed ETSM achieves 200MHz bandwidth with 78.5% peak efficiency.