Jooseung Kim

Optimization for Envelope Shaped Operation of Envelope Tracking Power Amplifier

This paper describes the analysis of an optimized envelope shaping function for the envelope tracking power amplifier (ET PA) and its implementation. The proposed shaping function, which is sweet spot tracking with crest factor reduction, improves the efficiency and output power of the power amplifier (PA), as well as its linearity. For an accurate simulation of the supply modulator, an equivalent model of the PA under the envelope shaping is suggested. To achieve high efficiency and wide bandwidth, the CMOS supply modulator has a hybrid structure of a switching amplifier and a linear amplifier. The fabricated ET PA delivers higher efficiency and better linearity than standalone PA for the wideband code division multiple access and long-term evolution signals.

A Multimode/Multiband Power Amplifier With a Boosted Supply Modulator

A multimode/multiband power amplifier (PA) with a boosted supply modulator is developed for handset applications. A linear broadband class-F amplifier is designed to have a constant fundamental impedance across 1.7-2 GHz and its second and third harmonic impedances are located at the high-efficiency area. To reduce the circuit size for handset application, the harmonic control circuits are merged into the broadband output matching circuit for the fundamental frequency. An envelope-tracking operation delivers high efficiency for the overall power. The linearity is improved by envelope tracking (ET) through intermodulation-distortion sweet-spot tracking at the maximum output power level. The efficiency and bandwidth (BW) are enhanced by a boosted supply modulator. Multimode operation is achieved by an ET technique with a programmable hysteresis control and automatic switching current adaptation of the hybrid supply modulator. For demonstration purpose, the PA and supply modulator are implemented using an InGaP/GaAs heterojunction bipolar transistor and a 65-nm CMOS process. For a long-term evolution signal, the envelope-tracking (ET) PA delivers a power-added efficiency (PAE) and an error vector magnitude of 33.3%-39% and 2.5%-3.5%, respectively, at an average power of 27.8 dBm across 1.7-2 GHz. For a wideband code-division multiple-access signal across 1.7-2 GHz, the ET PA performs a PAE, an ACLR1, and an ACLR2 of 40%-46.3%, from -39 to -42.5 dBc, and -51 to -58 dBc, respectively, at an average output power of 30.1 dBm. The ET PA with an EDGE signal delivers a PAE, an ACPR1, and an ACPR2 of 37%-42%, from -56.5 to -59.3 dBc, and -63.5 to -69.5 dBc, respectively, at an average power of 28 dBm across the 300-MHz BW. These results show that the proposed design achieves highly efficient and linear power amplification for multimode/multiband wireless communication applications.

Design of Bandwidth-Enhanced Doherty Power Amplifiers for Handset Applications

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-wave length transformer and propose a phase compensation circuit and an additional offset line to be incorporated into the matching net works for an enhanced BW of the Doherty PA. The quarter-wave length transformer and the final output circuit have the same Q. 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 mm2 die using an InGaP/GaAs hetero junction 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 ef ficiency (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.

Envelope-Tracking Two-Stage Power Amplifier With Dual-Mode Supply Modulator for LTE Applications

This paper presents an envelope tracking power amplifier (ET PA) using a dual-mode supply modulator for handset application. The supply modulator has a combined structure with a linear amplifier and a switching amplifier. The dual-mode supply modulator operates in high-power mode and low-power mode by providing the supply voltage of the linear amplifier of 5 and 2.5 V, respectively. For 1.74-GHz long-term evolution signal with 10-MHz bandwidth, 6.44-dB peak-to-average power ratio, and 16-quadrature amplitude modulation, the ET PA delivers a power-added efficiency (PAE) of 39.8%, an evolved universal terrestrial radio access adjacent channel leakage ratio (E-UTRAACLR) of - 35.7 dBc, and an error vector magnitude (EVM) of 3.81% at an average output power of 27 dBm. The ET PA also delivers a PAE of 22.6% at an average output power of 18 dBm, which is 6.6% higher than that of the conventional ET PA and 13.1% higher than that of the standalone PA. The supply modulator is connected to a drive stage and a power stage of the PA simultaneously for further enhanced efficiency at a power back-off region. The dual-mode two-stage ET PA delivers a PAE of 38.1%, an E-UTRAACLR of - 32.9 dBc, and an EVM of 4.74% at an average output power of 27 dBm. The dual-mode two-stage ET PA also delivers a PAE of 26.3% at an average output power of 18 dBm, which is 7.8% higher than that of the conventional two-stage ET PA and 16.7% higher than that of the standalone PA.

Push the Envelope: Design Concepts for Envelope-Tracking Power Amplifiers

As mobile communication systems evolve to handle higher data rates, their modulation schemes only become more complicated, generating signals with large bandwidth and high peak-to-averagepower ratio (PAPR). To amplify such signals with high efficiency, the power amplifier (PA) should have high efficiency not only at the peak power level but also at low power, especially over the maximum power generation region. To realize these PA characteristics, the drain bias voltage of the transistor can be modulated on the basis of the input envelope power to minimize the dc supply power. Thus, the drain bias voltage should follow the envelope of the modulated signal, and this is called envelope tracking (ET). Usually, the envelope is shaped to realize the optimum performance from the ET PA. The PA is biased close to class B, and the dc current is automatically adjusted to the power level. The resulting PA has high efficiency for all power levels, comparable to the maximum efficiency of the PA at high power. In practice, the efficiency is degraded somewhat at low voltage because of the knee effect, lower transconductance, and mismatch effect for different drain bias voltages.

Envelope-Tracking CMOS Power Amplifier Module for LTE Applications

An envelope-tracking (ET) CMOS power amplifier (PA) is fabricated using a 0.18- μm CMOS process. The module containing the supply modulator, the PA, and the output transformer is implemented on a printed circuit board (PCB). The CMOS PA employs the second and third harmonic controls at the input and the second harmonic short at the output for improved linearity. The impact on the nonlinearity of the cascode differential structure is studied and optimized. A proposed output transformer on the PCB minimizes the loss and enhances the efficiency of the PA. The ET on the gate of the common gate transistor is proposed to achieve high linearity and efficiency without using a digital pre-distortion technique. For a long-term evolution (LTE) signal at 1.85 GHz with a 10-MHz bandwidth and a 16QAM 7.5-dB peak-to-average power ratio, the ET CMOS PA module achieves a power-added efficiency of 34%, an error vector magnitude of 2.8%, and an adjacent channel leakage ratio of -34.2 dBc at an average output power of 26 dBm. The ET operation reduces the total current consumption by 10% to 34%, according to the power level, over that of the standalone PA for the LTE signal.

A Dual Power-Mode Multi-Band Power Amplifier With Envelope Tracking for Handset Applications

This paper presents a dual power-mode and multi-band power amplifier (PA) for handset applications that improves the efficiency in low-power regions. This PA operates in two modes through path control by a shunt switched capacitor. The proposed control method provides efficient mode control without any efficiency degrading and bandwidth (BW) limiting. The proposed PA, in conjunction with a boosted supply modulator for envelope tracking (ET) operation not only in the high-power mode, but also in the low-power mode, delivers good performance at all average output power levels. The linearity is improved by ET through a proper envelope-shaping method. For demonstrative purposes, the PA and supply modulator are implemented using an InGaP/GaAs heterojunction bipolar transistor and AIGaAs/InGaAs enhancement/depletion-mode pseudomorphic high electron-mobility transistor process and a 0.18-

A 34% PAE, 26-dBm output power envelope-tracking CMOS power amplifier for 10-MHz BW LTE applications

\mu

Wideband envelope tracking power amplifier for LTE application

m CMOS process, respectively. The ET PA is tested across the range of 1.7–2.0 GHz using a long-term evolution signal with 16 quadrature amplitude modulation, a 7.5-dB peak-to-average power ratio, and 10-MHz BW. The proposed dual power-mode multi-band ET PA delivers good performance for high- and low-power modes, indicating that the architecture is promising for handset PA applications.

Highly Efficient Dual-Switch Hybrid Switching Supply Modulator for Envelope Tracking Power Amplifier

An envelope tracking CMOS power amplifier is implemented in 0.18-µm CMOS, and achieves a PAE of 34%, an EVM of 3.2%, and an ACLR of −32.5 dBc at an average output power of 26 dBm and a frequency of 1.8 GHz for a 10-MHz BW 16 QAM 7.5-dB PAPR LTE signal. The envelope tracking operation improves a PAE by 2% to 6.5% over the stand-alone PA for the LTE signal.