This paper presents the first 28-/37-/39-GHz linear Doherty power amplifier (PA) in silicon for broadband fifth-generation (5G) applications. We introduce a new transformer-based on-chip Doherty power combiner that can reduce the impedance transformation ratio (ITR) in power back-off (PBO) and, thus, improve the bandwidth and power-combining efficiency. We also devise a “driver-PA co-design” method that creates power-dependent uneven feeding in the Doherty PA and enhances the Doherty operation without any hardware overhead or bandwidth compromise. For the proof of concept, we implement a 28-/37-/39-GHz PA fully integrated in a standard 130-nm SiGe BiCMOS process, which occupies 1.8 mm $^{\mathbf {2}}$ . The PA achieves a 52% −3-dB small-signal $\text{S}_{\mathbf {21}}$ bandwidth and a 40% −1-dB large-signal saturated output power ( $\text{P}_{\mathbf {sat}}$ ) bandwidth. At 28/37/39 GHz, the PA achieves +16.8−/+17.1−/+17-dBm $\text{P}_{\mathbf {sat}}$ , +15.2−/+15.5−/+15.4-dBm $\text{P}_{\mathbf {1\,dB}}$ , and superior 1.72/1.92/1.62 times efficiency enhancement over class-B operation at 5.9-/6-/6.7-dB PBO. Moreover, the PA demonstrates multi-gigabit-per-second data rates with excellent efficiency and linearity for 64-quadrature amplitude modulation (64-QAM) in three millimeter-wave (mm-wave) 5G bands. This PA advances the state of the art for Doherty, wideband, and 5G silicon PAs in mm-wave bands. It supports drop-in upgrade for current PAs in existing mm-wave systems and opens doors to compact system solutions for future multiband 5G massive multiple-input multiple-output (MIMO) and phased-array platforms.

A 28-/37-/39-GHz Linear Doherty Power Amplifier in Silicon for 5G Applications

Envelope tracking (ET) is by now a well-established technique that improves the efficiency of microwave power amplifiers (PAs) compared to what can be obtained with conventional class-AB or class-B operation for amplifying signals with a time-varying envelope, such as most of those used in present wireless communication systems. ET is poised to be deployed extensively in coming generations of amplifiers for cellular handsets because it can reduce power dissipation for signals using the long-term evolution (LTE) standard required for fourthgeneration (4G) wireless systems, which feature high peak-to-average power ratios (PAPRs). The ET technique continues to be actively developed for higher carrier frequencies and broader bandwidths. This article reviews the concepts and history of ET, discusses several applications currently on the drawing board, presents challenges for future development, and highlights some directions for improving the technique.

ET Comes of Age: Envelope Tracking for Higher-Efficiency Power Amplifiers

In this paper, a novel broadband Doherty power amplifier based on the continuous-mode technique (C-DPA) is proposed. The amplifier is focused on manipulating harmonic components in a Doherty power amplifier (DPA) structure to achieve improved bandwidth and efficiency. In a conventional DPA, harmonic isolation is typically required between the two transistors to prevent them from modulating each other at harmonic frequencies. However, as presented in this paper, such isolation is not actually necessary. On the contrary, by allowing the two transistors to modulate each other at harmonic frequencies with the help of a properly designed postharmonic tuning network, a series of highly efficient DPA modes can be created over a continuous frequency band, leading to a broadband C-DPA. Based on the proposed method, an example of a C-DPA working from 1.65 to 2.75 GHz was designed. According to the measured results, the designed C-DPA exhibits a 52%–66% efficiency at a −6 dB power backoff and a power utilization factor higher than 1.08 over the 1.1-GHz band. In addition, when simulated by a 7.5-dB peak-to-average power ratio 20-MHz LTE signal, the example C-DPA exhibits an efficiency of 46%–62% while maintaining an adjacent channel power ratio below −45 dBc after linearization over the full 1.1-GHz band. To the best of our knowledge, this is the first proposed C-DPA and a state-of-the-art performance for broadband DPAs.

A Broadband Doherty Power Amplifier Based on Continuous-Mode Technology

The Doherty power amplifier (DPA) architecture, in various formats using different technologies, has been a very popular means of providing high conversion efficiencies from raw electrical power to sophisticated modulated RF and microwave signals ever since the requirements for very high power amplitude modulated (AM) radio transmitters in the mid-1930's. This paper covers not only the “original stories” of high power tube-based Doherty power amplifiers for those early AM transmitters, but also provides many examples of implementations employing a range of modern semiconductor transistor and circuit technologies covering a wide range of power levels, modulation schemes and carrier frequencies.

The Doherty power amplifier

William H. Doherty was an American electrical engineer, best known for his invention of the Doherty amplifier. Born in Cambridge, Massachusetts, in 1907, Doherty attended Harvard University, where he received his bachelor's degree in communication engineering (1927) and his master's degree in engineering (1928). He then joined the American Telegraph and Telephone Company Long Lines Department in Boston. He remained there for a few months before joining the National Bureau of Standards, where he researched radio phenomena. Doherty joined Bell Telephone Laboratories (now Bell Labs) in 1929 and, while there, worked on the development of high power radio transmitters that were used for transoceanic radio telephones and broadcasting.

Doherty's Legacy: A History of the Doherty Power Amplifier from 1936 to the Present Day

A wideband high-power Doherty design technique enabling fractional bandwidths > 50% is described. It utilizes wideband impedance inversion, device output capacitance compensation and passive phase-optimized wideband input-signal splitting. As prove of concept a LDMOS based ultra-wideband broadcast Doherty amplifier is presented, which covers the UHF-TV 470MHz-803MHz (BW
 rel
 = 52%) band with average efficiencies between 38%-47% @P
 avg
 > 115W while maintaining peak power capability > 700W over the entire band. Predistortability is demonstrated by satisfying the digital TV linearity requirements (-38dBc) using a commercial DVB-T exciter. The proposed DPA is an excellent drop-in replacement for the low-efficiency wideband PA blocks currently in use in broadcast transmitters.

A 700-W peak ultra-wideband broadcast Doherty amplifier

A push-pull Doherty Power Amplifier (DPA) is proposed that uses a wideband power combiner BALUN, which is capable to provide the optimum fundamental and 2nd harmonic loading conditions over a large operating bandwidth to the active devices. A 700W DPA demonstrator using these techniques provides high average efficiency (> 40%) for a 7.5dB PAR DVB-T signal over a 37% relative RF-bandwidth.

L. C. N. deVreede

Papers

A 700-W peak ultra-wideband broadcast Doherty amplifier

A wideband 700W push-pull Doherty amplifier