Juyeon Lee

A Multimode/Multiband Envelope Tracking Transmitter With Broadband Saturated Amplifier

A multimode/multiband envelope tracking (ET) transmitter consisting of a hybrid switching amplifier (HSA) and a broadband saturated power amplifier (PA) is developed across 1.3 to 2.7 GHz. For the various standard signals with different bandwidth and peak-to-average power ratio, the HAS efficiently provides a supply signal to the PA by changing the reference value of the hysteresis comparator. The saturated amplifier employs the nonlinear output capacitor to shape the voltage waveform, resulting in the half-sinusoidal or rectangular waveform. Since the nonlinear capacitor generates harmonic component, the voltage shaping is mainly carried out by the capacitor and slightly supported by the harmonic loading circuit. Thus, with the harmonic load higher than the output capacitor, the saturated amplifier can operate with high efficiency. This characteristic enables the saturated PA to operate with broadband characteristic and high efficiency because the design is mainly focused on the fundamental matching problem. The broadband saturated PA is implemented based on load/source-pull methodology. Broadband matching networks for the high efficiency are synthesized by simplified real frequency technique. For the bandwidth from 1.3 to 2.7 GHz (70% fractional bandwidth), the measured output power, drain efficiency, and power-added efficiency (PAE) performances are between 39.8–42.0 dBm, 55.8–69.7%, and 51.2–65.3%, respectively. The ET transmitter is demonstrated at 1.8425-GHz long-term evolution (LTE), 2.14-GHz wideband code division multiple access (WCDMA), and 2.6-GHz mobile worldwide interoperability for microwave access (m-WiMAX) applications. It delivers the PAE of 32.16, 37.24, and 28.75% for LTE, WCDMA, and m-WiMAX applications, which are improved by 3.1, 4.2, and 1.7%, respectively.

Highly Efficient Saturated Power Amplifier

In this article, a high-efficiency saturated amplifier has been presented. This amplifier takes advantage of the nonlinear output capacitor to shape the voltage waveform. The nonlinear capacitor generates substantial second harmonic voltage with small higher order harmonics. Thus, using √2 times larger fundamental load and the proper second harmonic termination, the resultant voltage waveform can be half-sinusoidal. For high efficiency, the PA should be driven by the large input power. Therefore, the current of the PA is bifurcated, resulting in the quasirectangular current shape. The resultant output waveforms are similar to those of class-F1 amplifiers, whose waveforms are optimal for high efficiencies. Based on harmonic source/ load-pull simulation, the saturated amplifier has been designed using Crees GaN HEMT CGH40006P packaged model. The matching networks for the input and output were optimized using the Momentum simulator. The implemented amplifier delivered a PAE of 80.1% at 3.475 GHz. The simulation and measurement results verify that the saturated amplifier is suitable for a high-efficiency PA over a relatively high frequency band.

A highly efficient asymmetric Doherty Power Amplifier with a new output combining circuit

An asymmetric Doherty Power Amplifier (ADPA) is introduced using a new output combining circuit for easy of implementation with a large matching tolerance. The proposed APDA has been implemented using GaN HEMT devices at 2.6 GHz for WiMAX signal with 5MHz bandwidth and 8.3 dB peak to average power ratio. This ADPA delivers a saturated output power of 51.7 dBm and a drain efficiency of 60.4% at an average output power of 43.6 dBm. After linearization using digital feedback predistortion technique, the ADPA satisfies the linearity specification with −51.98 dBc of adjacent channel leakage ratio at 10MHz offset. To the best of our knowledge, the drain efficiency of 60.4% is the highest efficiency at 2.6GHz frequency for a WiMAX signal with 8.3dB PAPR.

Fully Integrated CMOS Saturated Power Amplifier With Simple Digital Predistortion

A highly efficient CMOS saturated power amplifier (PA) is implemented. The efficiency is enhanced by the voltage waveform engineering using the second harmonic component generated by the nonlinear output capacitor (Cout). For an improved linearity to satisfy the specification of handset applications, a simple open-loop digital predisortion algorithm is employed. The fully integrated single-stage differential PA including the output transformer is fabricated using a 0.18- μm CMOS process. The PA with 3.5 V supply delivers good performance across the 1.7-2.0 GHz frequency band.

Asymmetric Broadband Doherty Power Amplifier Using GaN MMIC for Femto-Cell Base-Station

A power amplifier (PA) for a femto-cell base station should be highly efficient and small. The efficiency for amplification of a high peak-to-average power ratio (PAPR) signal is improved by designing an asymmetric Doherty power amplifier (DPA). From the simulation result for a long-term evolution (LTE) signal with 7.2-dB PAPR, the DPA delivers the highest efficiency with 1:1.4 cell size ratio for the carrier and peaking PAs. A small size is achieved by designing the DPA using a GaN monolithic microwave integrated circuit process. For broadband operation, we employ a new circuit topology to alleviate the bandwidth limiting factors of the DPA such as a quarter-wavelength transformer, phase compensation network, and offset line. With the design concept, an asymmetric broadband DPA is implemented using a TriQuint 3MI 0.25-μm GaN-HEMT MMIC process. Across 2.1-2.7 GHz, the implemented PA deliver a drain efficiency of over 49%, a gain of over 12.6 dB, and adjacent channel leakage ratio of below -45 dBc at an average power of over 33.1 dBm for the LTE signal. This fully integrated circuit has a chip-size of 2.65 mm×1.9 mm.

A multimode/multiband envelope tracking transmitter with broadband saturated power amplifier

A multimode/multiband envelope tracking (ET) transmitter consisting of a hybrid switching amplifier (HSA) and a broadband saturated power amplifier (PA) is developed across 1.3 to 2.7 GHz. For the various standard signals with different bandwidth and peak-to-average power ratio, the HSA efficiently provides a supply signal to the PA by changing the reference value of the hysteresis comparator. The broadband saturated PA, taking advantage of a nonlinear output capacitor to shape the voltage waveform, is implemented based on load/source-pull methodology. Broadband matching networks for the high efficiency are synthesized by simplified real frequency technique. For the bandwidth from 1.3 to 2.7 GHz (70% fractional bandwidth), the measured output power, drain efficiency, and power-added efficiency (PAE) performances are between 39.8–42.0 dBm, 55.8–69.7%, and 51.2–65.3%, respectively. The ET transmitter is demonstrated at 1.8425-GHz long-term evolution (LTE), 2.14-GHz wideband code division multiple access (WCDMA), and 2.6-GHz mobile world wide interoperability for microwave access (m-WiMAX) applications. It delivers the PAE of 32.16, 37.24, and 28.75% for LTE, WCDMA, and m-WiMAX applications, which are improved by 3.1, 4.2, and 1.7%, respectively.

Accurate Offset Line Design of Doherty Amplifier With Compensation of Peaking Amplifier Phase Variation

Accurate offset line design of Doherty amplifier is investigated to compensate the phase variation of the carrier and peaking amplifiers. The offset line at the peaking amplifier not only blocks the power leakage to the peaking amplifier at the OFF-state, but also assists in the load modulation like the offset line at the carrier amplifier. However, with the conventional offset line, the load is not properly modulated due to the phase variation of the class C peaking amplifier. Since the offset lines at the carrier and peaking power amplifiers (PAs) properly eliminate the reactive parts during the Doherty load modulation, the offset lines can handle the phase variation also. To compensate the phase variation, additional lines are added at the carrier and peaking amplifiers for the proper load modulation. With the new offset line, the load of the peaking amplifier can be properly modulated and the efficiency at the high power region is increased. In addition, the efficiency at the low power region is also increased due to the larger load of the carrier amplifier at the power region. The enhanced performance is validated by the Doherty PA employing CGH40045 devices at 1.94 GHz, applying drain bias voltage of 50 V. For the long term evolution signal with a 6.5 dB peak-to-average power ratio, the Doherty amplifier with the new offset line delivers a drain/power-added efficiency of 57%/54.8% which is 3.5%/3.1% higher than that with the conventional offset line at an output power of 45.4 dBm with the linearity -48.3 dBc using digital predistortion linearization.

Highly Linear 2-Stage Doherty Power Amplifier Using GaN MMIC

A power amplifier (PA) for a femto-cell base station should be highly efficient, linear and small. The efficiency for amplification of a high peak-to-average power ratio (PAPR) signal was improved by designing an asymmetric Doherty PA (DPA). The linearity was improved by applying third-order inter-modulation (IM3) cancellation method. A small size is achieved by designing the DPA using GaN MMIC process. The implemented 2-stage DPA delivers a power-added efficiency (PAE) of 38.6% and a gain of 33.4 dB with an average power of 34.2 dBm for a 7.2 dB PAPR 10 MHz bandwidth LTE signal at 2.14 GHz.

Mitigating Phase Variation of Peaking Amplifier Using Offset Line

The effect of the peaking offset line on the Doherty amplifier operation is investigated. The peaking amplifier of the Doherty structure operates at a C-bias condition for the load modulation. With the C-bias, the amplifier has a poor AM-PM characteristic due to the nonlinear input/output capacitances. The nonlinear phase variation of the peaking amplifier influences the load modulation behavior and reduces efficiency of the Doherty amplifier at a high output power region. To mitigate the nonlinear PM characteristic of the peaking amplifier, the length of the peaking offset line should be reduced from the conventional offset line. To validate the offset line design, a 2-stage Doherty amplifier is implemented at 2.655 GHz using GaN pHEMT. Due to the proper load modulation, the Doherty PA delivers a very good performance. For the LTE signal with 20 MHz bandwidth and 7.2 dB peak-to-average power ratio (PAPR), the amplifier delivers a power-added efficiency (PAE) of 49.3% and gain of 25 dB at an average output power of 49 dBm.

GaN HEMT MMIC Doherty Power Amplifier With High Gain and High PAE

This paper presents an approach to maximize the gain and power-added efficiency (PAE) of a Doherty power amplifier (PA) using a 0.25 μm GaN pHEMT. The conventional carrier PA has an input matching for the ROPT load and does not deliver the 3 dB higher gain with 2ROPT load due to the mismatch and it degrades gain and PAE of the PA. To solve the problem, the input match of the carrier PA is optimized at the back-off power level with the 2ROPT output load, while the input is mismatched at a high power level. A Doherty PA with the concept is designed and implemented using a GaN pHEMT MMIC process at 1.8 GHz. The measured average output power, power-added efficiency and gain are 35.6 dBm, 56.3%, and 18.9 dB for a 10 MHz LTE signal with a 6.5 dB PAPR.