13.5 A 0.35-to-2.6GHz multilevel outphasing transmitter with a digital interpolating phase modulator enabling up to 400MHz instantaneous bandwidth

IEEE J. Solid-State Circuits

Roverato³

et al. 2019

Self Cite

We present a prototype RF transmitter with an integrated multilevel class-D power amplifier (PA), implemented in 28-nm CMOS. The transmitter utilizes tri-phasing modulation, which combines three constant-envelope phase-modulated signals with coarse amplitude modulation in the PA. This new architecture achieves the back-off efficiency of multilevel outphasing, without linearity-degrading discontinuities in the RF output waveform. Because all signal processing is performed in the time domain up to the PA, the entire system is implemented with digital circuits and structures, thus also enabling the use of synthesis and place-and-route CAD tools for the RF front end. The effectiveness of the digital tri-phasing concept is supported by extensive measurement results. Improved wideband performance is validated through the transmission of orthogonal frequency-division multiplexing (OFDM) bandwidths up to 100 MHz. Enhanced reconfigurability is demonstrated with noncontiguous carrier aggregation and digital carrier generation between 1.5 and 1.9 GHz without a frequency synthesizer. For a 20-MHz 256-QAM OFDM signal at 3.5% error vector magnitude (EVM), the transmitter achieves 22.6-dBm output power and 14.6% PA efficiency. Thanks to the high linearity enabled by tri-phasing, no digital predistortion is needed for the PA.

Section: A Phase Modulatorsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

A 1.5–1.9-GHz All-Digital Tri-Phasing Transmitter With an Integrated Multilevel Class-D Power Amplifier Achieving 100-MHz RF Bandwidth

Lemberg

IEEE J. Solid-State Circuits

Roverato³

et al. 2019

Self Cite

“…The ACLR degradation caused by the BB component can be somewhat alleviated by using a sample rate that is not equal to the carrier frequency or any of its integer fractions, thus moving the sampling image away from the signal band. This solution is made possible by the digital interpolating phase modulator (DIPM), which is capable of generating a phasemodulated signal at any carrier frequency within certain limits [13], [15]. Fig.…”

Section: A Unequal Sample Rate and Carrier Frequencymentioning

confidence: 99%

“…Among such transmitters, the optimal back-off power efficiency is typically achieved by architectures that utilize constant-envelope phase-modulated signals and a separate discrete-level amplitude signal. Specifically, this category includes polar [1]- [7] and multilevel outphasing transmitters [8]- [13].…”

Section: Introductionmentioning

confidence: 99%

Spectral Effects of Discrete-Time Amplitude Levels in Digital-Intensive Wideband Radio Transmitters

2018 IEEE International Symposium on Circuits and Systems (ISCAS)

Stadius

Lemberg

et al. 2018

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This paper examines one source of spectral degradation in polar and multilevel outphasing transmitters. The degradation is caused by the amplitude signal appearing at the transmitter output as a baseband component, in addition to the desired RF signal. This baseband component contains sampling images and quantization noise across the spectrum. Thus, it adds noise at the signal band where it cannot be filtered and limits the achievable ACLR, particularly in wideband LTE and 5G systems. We analyze the origin of this phenomenon and related effects of system and signal parameters, and propose three design solutions for eliminating or alleviating the problem. Our analysis and simulations demonstrate that using a voltage-subtracting power combiner cancels the described degradation, potentially leading to significant improvement in spectral performance.

“…A previously proposed solution for improving the back-off efficiency is multilevel outphasing, in which the output amplitude is modulated by discrete amplitude levels in addition to a phase offset [3], [4]. In our earlier work, we have developed new circuit solutions for phase modulators [5] and PAs [6] intended for highly integrated wideband multilevel outphasing transmitters [7]. However, while analyzing the characteristics of multilevel outphasing, we have found that amplitude-level transitions inherently cause discontinuities in the harmonic content of the combined output signal [8].…”

mentioning

confidence: 99%

A Class-D Tri-Phasing CMOS Power Amplifier With an Extended Marchand-Balun Power Combiner

IEEE Trans. Microwave Theory Techn.

Ryynänen

Stadius

et al. 2020

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This paper presents a power amplifier (PA) design, which consists of eight class-D PA units on a single 28-nm CMOS die and a coupled-line power combiner on printed circuit board (PCB). The PA utilizes tri-phasing modulation, which combines polar and outphasing components in a way that eliminates linearity-degrading effects of multilevel outphasing while maintaining the back-off efficiency. Each PA unit contains a cascoded output stage with a 3.6-V supply voltage, and multilevel operation is enabled by on/off logic circuitry. Our analysis shows that the choice of power-combiner type is vital for reducing PA supply and ground ripple and thus ensuring reliable operation. Accordingly, the power combiner is implemented with extended Marchand baluns, which consist of input transmission lines and coupled-line sections. Unlike the original Marchand balun, our new topology is feasible for implementation under the layout restrictions caused by the multiple-unit PA on a single die. Measurement results show the PA achieving a peak output power of 29.7 dBm with a 34.7% efficiency, and operation with aggregated LTE signals at 1.7-GHz carrier frequency is verified with bandwidths up to 100 MHz.