A Wide-Bandwidth Supply Modulator using Binary Switched-Capacitor dc-to-dc Converters

In this paper, we propose to implement the switching regulator in an envelope-tracking (ET) hybrid supply modulator (HSM) using a binary switched-capacitor (SC) dc-to-dc converter instead of a switched-inductor (SL) dc-to-dc converter. The output impedance of a SL converter is inductive in nature, which prevents the delivery of the high-frequency content of the envelope in wide-bandwidth signals. On the other hand, the proposed SC supply modulator is not limited by an inductive impedance, and hence, inherently exhibits immediate response, which facilitates high-efficiency ET despite the increasing bandwidth of RF signals. Additionally, SC supply modulators require only switches and capacitor, which can be integrated on the same transmitter microchip using the high-Q capacitors available in typical CMOS processes. Conversely, existing supply modulators require multiple off-chip or in-package inductors to realize high efficiency, which increase form factor and cost. Circuit simulation results in 0.18µm demonstrate the efficiency advantage of the proposed SC HSM over an SL HSM, where up to 11.7% improvement in the average efficiency is realized while tracking a 100-MHz bandwidth OFDM signal.