Key Takeaways & Executive Findings
- •• A K/Ka-band series Doherty PA with a distributed impedance inverting network achieves wideband linearity and power back-off efficiency enhancement. • Implemented in 65 nm CMOS, the PA delivers a 3 dB bandwidth of 15.5 GHz with a peak gain of 21.2 dB at 34.2 GHz. • Under 1-V supply, it achieves OP1dB >13.4 dBm and Psat >16 dBm from 21 to 30 GHz, with peak PAE of 28.2% and 6-dB PBO PAE of 13.2%. • Without DPD or equalization, the PA meets stringent EVM requirements for high-order modulated signals, including −25.2 dB for 200 MHz 64-QAM and −20 dB for 2 GHz 16-QAM at 27 GHz.
Abstract
A two-way K/Ka-band series-Doherty PA (SDPA) with a distributed impedance inverting network (IIN) for millimeter wave applications is presented in this article. The proposed distributed IIN contributes to achieve wideband linear and power back-off (PBO) efficiency enhancement. Implemented in 65 nm bulk CMOS technology, this work realizes a measured 3 dB bandwidth of 15.5 GHz with 21.2 dB peak small-signal gain at 34.2 GHz. Under 1-V power supply, it achieves OP1dB over 13.4 dBm and Psat over 16 dBm between 21 to 30 GHz. The measured maximum Psat, OP1dB, peak/OP1dB/6dBPBO PAE results are 17.5, 14.7 dBm, and 28.2%/23.2%/13.2%. Without digital pre-distortion (DPD) and equalization, EVMs are lower than −25.2 dB for 200 MHz 64-QAM signals. Besides, this work achieves −33.35, −23.52, and −20 dB EVMs for 100 MHz 256-QAM, 600 MHz 64-QAM and 2 GHz 16-QAM signals at 27 GHz without DPD and equalization.
1. Introduction
The 5G NR has defined FR2 n257 (26.5−29.5 GHz) and FR2 n258 (24.25−27.5 GHz) for wireless communication in millimeter-wave bands, which promises sufficient spectrum resources in contrast with FR1. To meet the high data rate throughput in 5G FR2 band, mm-wave communication systems typically employ high-order modulation schemes, such as 16-QAM, 64-QAM, and 256-QAM modulated signals. However, those signals are with high peak-to-average power ratio (PAPR), requiring an excellent linear and PBO efficiency performance of the transmitting system. For instance, PAPRs of 16-QAM and 64-QAM SC signals are in the range of 6 to 7 dB and PAPRs of 16-QAM and 64-QAM OFDM signals are in the range of 10 to 11 dB[1]. As the output module of the transmitting system, the PA determines the overall performance in terms of linearity and efficiency to a large extent.
To meet the strict EVM requirement and to minimize the power consumption when PA works at the average power status, several kinds of efficiency enhancement techniques for linear PAs have been proposed[2]. A conventional outphasing power amplifier divides a non-constant envelope signal into two constant envelope signals at input and sums them in vector at output, achieving an excellent amplitude modulation of two phase-modulated (PM) signals[3, 4]. To generate two PM signals for accurate linear output, an extra wideband digital modulator is needed and thus increases the difficulty of circuit design and integration. The working principle of envelop-tracking (ET) power amplifier can be explained as a similar envelope-derived modulation to the supply voltage of a traditional linear power amplifier[5, 6]. However, a high-speed supply modulator is often difficult to design, causing the misalignment of amplitude information and phase information under the wideband operation.
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Xinyu Jiang, Wei Deng, Junlong Gong, Haikun Jia, Baoyong Chi (2025). A K/Ka-band series Doherty CMOS power amplifier with distributed multi-step impedance inverting network. SinoTechIntel Verified Research. https://doi.org/10.1088/1674-4926/25010002
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Frequently Asked Questions
What is the key innovation of this K/Ka-band Doherty PA?
The key innovation is the distributed multi-step impedance inverting network (IIN) that enables wideband linearity and power back-off efficiency enhancement in a series Doherty configuration.
What are the main performance metrics of the proposed PA?
The PA achieves a 3-dB bandwidth of 15.5 GHz, peak gain of 21.2 dB at 34.2 GHz, OP1dB >13.4 dBm, Psat >16 dBm from 21-30 GHz, and peak PAE of 28.2% with 6-dB PBO PAE of 13.2%.
How does the PA perform with modulated signals?
Without DPD or equalization, it achieves EVM lower than -25.2 dB for 200 MHz 64-QAM, and -33.35 dB for 100 MHz 256-QAM, -23.52 dB for 600 MHz 64-QAM, and -20 dB for 2 GHz 16-QAM at 27 GHz.
What technology is used for implementation?
The PA is implemented in 65 nm bulk CMOS technology, operating under a 1-V power supply.
What are the target applications?
The PA is designed for millimeter-wave 5G FR2 bands (n257 and n258) and other high-data-rate wireless communication systems requiring high linearity and efficiency.
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