A Simple and Adjustable Technique for Effective Linearization of Power Amplifiers Using Harmonic Injection

Abstract

A simple and effective method for linearization of power amplifiers (PAs) is proposed. The method is based on the second harmonic injection into the input of the PA. The second harmonic is generated in a feedback path by taking the low-power transistors of a pseudo-differential pair amplifier to their nonlinear regime. The amplitude and phase of the second harmonics are controlled by tunable matching networks of the pseudo-differential pair which include trimmer capacitors. Using a theoretical analysis, we show that the proposed method is capable of canceling the third-order intermodulation signal at the PA output. As a proof of concept, a 10-W PA in a frequency band of 1.4-1.6 GHz is designed and linearized. By fabricating both the reference and linearized PAs and performing measurements under several conditions, it is experimentally demonstrated that applying the proposed scheme, thanks to its adjustability, highly linearizes the PA in a wide bandwidth and a wide range of output power. INDEX TERMS adjacent channel power ratio, intermodulation distortion, power amplifiers, linearization techniques, second harmonic injection, tunable matching network.

A highly linearized second harmonic injected GaN power amplifier

“…For this purpose, a two‐tone test 21 simulation was performed using Advanced Design System (ADS) on a 10‐W PA, which is shown in Figure 1B. This PA meets a small signal gain of 17 dB, OP1dB of 33.5 dBm, and 40 dBm Pout at the 3‐dB compression point in its operating bandwidth, 1.3–1.7 GHz 18 …”

“…This PA meets a small signal gain of 17 dB, OP1dB of 33.5 dBm, and 40 dBm Pout at the 3-dB compression point in its operating bandwidth, 1.3-1.7 GHz. 18 Figure 2A presents the IMD3 simulation result, which was carried out at 1.5 GHz with a 10 MHz frequency interval ( f 1 = 1.495 GHz, f 2 = 1.505 GHz). At different Pout levels, the amplitude and phase of the injected SHs were optimized to achieve a minimum IMD3 level.…”

“…The significant advantages of this technique include good linearization with increased 1‐dB compression point, great simplicity, and low‐cost implementation. It is worth noting that in this method, unlike feedback SHI methods such as Abbasnezhad et al, 18 no directional coupler is required at the PA's output, preventing additional losses, hence a higher PAE and Pout at the 1‐dB compression point. Moreover, in Abbasnezhad et al, 18 the feedback path may cause circuit instability, so a stability analysis of the whole network (including both the PA and SHG) is required.…”

“…It is worth noting that in this method, unlike feedback SHI methods such as Abbasnezhad et al, 18 no directional coupler is required at the PA's output, preventing additional losses, hence a higher PAE and Pout at the 1‐dB compression point. Moreover, in Abbasnezhad et al, 18 the feedback path may cause circuit instability, so a stability analysis of the whole network (including both the PA and SHG) is required. While in the proposed method, the SH is injected through a direct rather than feedback path, and the stability of the PA and SHG can be analyzed separately.…”

“…Also, in, 17 the SHI improves the adjacent channel power ratio of a pHEMT amplifier by 16 dB modulated by the CDMA signal. Recently, we proposed a simple and efficient linearization method based on the SHI in a feedback path to the input of a GaN PA. 18 In this study, the output signal of the PA is sampled using a directional coupler and given to a nonlinear second harmonic generator (SHG) network producing a second harmonic (SH) signal with adjustable amplitude and phase. This method showed a good linearizing performance in wide frequency bandwidth and various output power back-offs (OBOs) of the PA.…”