Linearity‐optimized GaN HEMT Doherty amplifiers using derivative superposition technique for WCDMA applications

Abstract

One prototype of the bandpass filter was fabricated on 0.8-mmthick substrate dielectric with constant r ϭ 2.65. The measured results with HP8510C are illustrated in Figure 5, as well as the simulated results with HFSS, very good agreement can be observed. The maximum pass band insertion loss is less than 1.5 dB and the in-band return losses, S11, are all less than Ϫ20 dB, even reaching Ϫ37dB at the transmission pole at 5.34 GHz. It can also be observed that the rejection band extends from 6.4 GHz to 7.8 GHz, about 20% bandwidth; the maximum rejection even reaches 50 dB, implying good potential to suppress the unwanted harmonics. CONCLUSIONSA novel bandpass filter is proposed and implemented in this letter, which is implemented with combination of two quite different electromagnetic structures-CSRR and SIW. The design strategies are discussed; one prototype was fabricated to demonstrate the validity of proposed techniques. The measured results imply good in-band behaviors with insertion loss less than 1.5 dB and good return losses all less than Ϫ20 dB. In addition, the highlight lies in the sharp out-of-band rejection; the maximum rejection almost reaches 50 dB, the stopband width is about 20% at Ϫ20 dB. plementary split ring resonators, IEEE Microwave Wireless Compon Lett 14 (2004), 280-282. 4. J. Garcia-Garcia, I. Gil, M.F. Portillo, and M. Sorolla, Equivalentcircuit models for split-ring resonators and complementary split-ring resonators coupled to planar transmission lines, IEEE Trans Microwave

Doherty power amplifier with feedforward linearization

“…The references use Fig.1 to represent the IM3 figure vs. different bias voltage [5]- [7]. It should be point out that this figure could not represent the case precisely.…”

“…These bring convenience to the amplifier design and tune. The references used parallel offset lines to prevent power leakage at the low power period (when the peaking amplifier is cut-off) [3]- [7], but when if the additional transmission line is added to the output network of the carrier amplifier, the quarter 50 Ohm impedance will be changed longer, hence the carrier amplifier will see a complex impedance rather than a real 100 Ohm during the low power period, the changed output impedance may lead to a performance degradation. To avoid the impedance change, the offset line of the carrier amplifier is moved to the input stage in this paper, so the quarter 50 Ohm transformer remains unchanged.…”

“…Doherty power amplifier (DPA) is regarded for its high efficiency on high data rate communications, other efficiency enhancement techniques such as EE&R and LINC have many drawbacks on such applications [3], [4]. What's more, the Doherty technique can enhance the efficiency of the power amplifier without reduce the linearity performance by using IMD cancellation technique in recent years [5]- [7]. As modern wireless communication systems require extremely high linearity, the Doherty technique is usually combined with additional linearization techniques such as digital predistortion [1] or feedforward linearization [3].…”

Analysis and experiment for drain bias dependence of IMD sweet spots in GaN HEMT power amplifier

“…To internally improve linearity, derivative superposition methods with the optimum gate bias control have been developed, but need two or more parallel composition of the transistors [2]. For a single-ended PA, the intermodulation distortion (IMD) is strongly cancelled or improved by the internal phenomenon, which is called as IMD sweet spots or IMD null.…”

“…However, gallium nitride high-electron mobility transistors (GaN HEMTs) have been recently developed and regarded as a promising candidate for high-power RF applications with several advantages of very high power densities, high electron saturation velocity, high operating temperature, and high cutoff frequency compared with any other technologies [2,7].…”