Abstract
This paper presents and demonstrates the design of a filter-less transmitter architecture with digitally assisted harmonic cancellation. A neural network is used to model the harmonics as well as IMD for digital predistortion applications. This neural network-based harmonic modeling does not require any reference signal to be injected at the input of PA, thereby reducing the complexity in characterizing the harmonics. An in-house 10 W PA operating from VHF to L-band has been designed and characterized for its harmonic suppression. This PA is used along with agile RF transceiver AD9361 from Analog Device and Xilinx embedding platform using Zynq ZC-706 system-on-chip for implementing the entire transmitter. The receiver of AD9361 captures the nonlinearity of the PA in terms of harmonics as well as intermodulation distortion (IMD) components for modeling and predistortion. The proposed architecture can handle all types of distortions due to hardware as well as PA nonlinearity. Besides, it is also able to cancel the harmonics using a harmonic injection in the feed-forward configuration. This transmitter architecture has the advantages of being low cost, filter-less, wideband, frequency agile, reconfigurable and less bulky compared to the conventional scheme. The proposed scheme is demonstrated to transmit 5 MHz LTE signal at different frequencies over the range of 100 MHz to 400 MHz. In such a case, the second and third harmonics appear over the frequency range from 200 MHz to 1.2 GHz, which are within the amplification range of PA, yet they are suppressed without using any filter at the output. More than -40 dBc harmonic rejection is achieved over the entire operating range of this filter-less transmitter. The adjacent channel leakage ratio (ACLR) is always better than -45 dBc after applying digital predistortion.
Highlights
The rapid evolution of wireless standards demands a radio platform that is transparent to all the existing standards
This paper presents a new filter-less transmitter architecture capable of compensating 2nd and 3rd harmonics generated by power amplifier (PA) using a digitally assisted feed-forward harmonic cancellation scheme
One can see that the digital predistortion (DPD) model is applied in channel transmitting the fundamental signal, whereas, the harmonic generation model is employed in the baseband of the auxiliary transmitter path used for feedforward cancellation
Summary
The rapid evolution of wireless standards demands a radio platform that is transparent to all the existing standards. To employ these models in feed-forward cancellation requires the signals injection at both the input and output at harmonic frequencies This results in more complex and bulky architecture as the number of harmonics increases. The original baseband signal, when processed through these models in the digital domain, will generate harmonic components for feed-forward signals as well as predistorted signals for IMD cancellation. One can see that the DPD model is applied in channel transmitting the fundamental signal, whereas, the harmonic generation model is employed in the baseband of the auxiliary transmitter path used for feedforward cancellation. The following sections discuss behavioral modeling of nonlinear distortions and harmonics of PA using NN
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
