This work discusses the efficiency bandwidth constrains in Doherty amplifiers. An analysis of the bandwidth limitations imposed by the impedance inverter and output capacitance of the active devices is given. Alternative wideband matching and output connection schemes for Doherty amplifiers are evaluated for their efficiency performance both at full output power, as well as, in power back-off operation. The presented theory is verified using a Doherty demonstrator amplifier, which allows independent control of the input signals for the main and peak device. The related measurements show the largest high-efficiency bandwidth reported up to date for a Doherty amplifier.

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