Abstract
A novel architecture of a digital modulated polar phased-array transmitter with phase modulation (PM) phase-shifting and feed-forward controlled dynamic matching (FFCDM) is presented in this article. Phase-shifting in a PM signal path is utilized in each element, which shares many components including a phase modulator, baseband, and IF components. The characteristics of the proposed architecture are analyzed. With a constant envelope of PM signals, the implicit nonlinearity of the phase shifter in this architecture has low impact on the linearity performance of a phased-array system. Meanwhile, low phase error can be achieved by high-resolution phase interpolation with the digital predistortion (DPD) technique. Efficiency for both saturated and 6-dB back-off power is enhanced by digital power amplifier (DPA) with FFCDM. As a proof of concept, a 3–7 GHz 4-element phased-array transmitter is designed and fabricated in 40-nm CMOS based on the proposed method. The measured root-mean-square (rms) phase error of 0.3°, effective phase shifting resolution of 9-bit, and peak system efficiency of 38.2% are achieved. For 40 MHz 64-QAM modulation signal, it exhibits EVM of 5.38% and 5.37%, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P_{\text {out}}$ </tex-math></inline-formula> of 14.30 and 14.46 dBm, and PAPR of 7.08 and 6.97 at 3.5 and 5.2 GHz, respectively. The measured peak EIRP is 35.6 dBm with a unit antenna gain of 2.98 dBi at 5 GHz. The radiation patterns with 0°, 15°, 30°, and 45° steering are measured based on monopole antennas. Meanwhile, the array achieves < 4.7% and < 5.9% EVM for 64-QAM signals with bandwidths of 20 and 40 MHz, respectively.
Highlights
P HASED-ARRAY transmitters (TXs) with beam steering, large instantaneous bandwidth, and high spectrum efficiency are highly demanded for high-speed wireless links with wide coverage and multi-standard
The proposed architecture shows the following advantages: 1) it decreases the impact of nonperfect phase shifters on the system, including nonlinearity and amplitude variation; 2) it shares many components as Radio frequency (RF) phase-shifting, where the circuit topology is simplified with potentially smaller size and power consumption; and 3) the system efficiency is improved with good linearity by digital modulated polar TX
Since the amplitude control word (ACW) or phase modulation (PM) code is changed at the same time (i.e., 300 nS) in state 1 and state 2, the difference between setting time T1 and T2 represents the delay mismatch between amplitude modulation (AM) and PM paths
Summary
P HASED-ARRAY transmitters (TXs) with beam steering, large instantaneous bandwidth, and high spectrum efficiency are highly demanded for high-speed wireless links with wide coverage and multi-standard. The design of phased array TXs with compact circuit size, high linearity, low amplitude variation, and high spectrum efficiency still remains challenges. Phasedarray system with high phase resolution can improve the signal integrity in wide transmission range and reduce the system size with smaller antenna spacing. Digital phase shifter with vector sum achieves high-resolution phase-shifting. A 3–7 GHz 4-element digital modulated polar phased-array TX in 40-nm LP CMOS is designed and fabricated [35]. It achieves 9-bit effective phase resolution with an root-mean-square (rms) phase error of 0.3◦, rms amplitude error of 0.2 dB, and peak system efficiency of 38.2%.
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