Design of Bandwidth-Enhanced Doherty Power Amplifiers for Handset Applications

Abstract

A quarter-wavelength impedance transformer as well as a number of other factors limit the bandwidth (BW) of Doherty power amplifiers (PAs). We utilize the lower Q of a quarter-wavelength transformer and propose a phase compensation circuit and an additional offset line to be incorporated into the matching networks for an enhanced BW of the Doherty PA. The quarter-wavelength transformer and the final output circuit have the same . Input dividing networks are also analyzed for operation of broad BW. The Doherty PA for long term evolution (LTE) applications is integrated into a 1.4 1.4 mm 2 die using an InGaP/GaAs heterojunction bipolar transistor (HBT) process. For an LTE signal with a 7.5-dB peak-to-average power ratio (PAPR) and a 10-MHz BW, the PA with a supply voltage of 4.5 V delivers a power-added efficiency (PAE) of 36.3% and an adjacent channel leakage ratio (ACLR) of 32 dBc with an average output power of 27.5 dBm at a frequency of 1.85 GHz. Across frequencies from 1.6-2.1 GHz, the PA performs with a PAE of more than 30%, a gain of more than 28 dB and an ACLR of less than 31 dBc at an average output power of 27.5 dBm while satisfying the standard spectrum mask. These figures verify that the proposed bandwidth enhancement techniques are effective for handset Doherty PAs.

A High Efficiency Doherty Power Amplifier for TV Band Applications

“…The percentage bandwidth of this DPA is 58.06% which is higher than that of the class AB power amplifier and higher than Doherty power amplifiers previously designed such as in [13], [15], and [17].…”

“…Although significant improvements in bandwidth have been reported recently [13]- [17], the DPA is still fundamentally bandwidth limited by the quarter wave impedance inverter needed to obtain proper load modulation. This results in substantial frequency dependence at the back-off power region where the Power Amplifier (PA) is operating most of the time, and thereby narrow band performance for realistic signals.…”

A Broadband High-Efficiency Doherty Power Amplifier With Integrated Compensating Reactance

“…Therefore, assuming both two amplifiers can achieve output current with the same amplitude over the whole frequency band (i.e., δ=1) and the phase of the peaking amplifier φ equals -θ, the normalized load impedances Z C_low , Z C_sat and Z P_sat can be calculated according to (6), (8) and (9), and the results are illustrated in Fig. 2.…”

A Wideband Doherty Power Amplifier With Shunted Reactive Load for Efficiency Enhancement

“…This results in the degradation of back-off efficiency and limits the bandwidth of the DPA. Although several designs have been proposed to extend the bandwidth [10][11][12][13][14][15][16][17][18][19][20][21][22], many of them are still complicated for realization. Recently, a novel output combiner employing a resonance LC tank was reported in the frequency band of 0.7-0.95 GHz [15].…”