Rui Fiel Cordeiro

Gigasample Time-Interleaved Delta-Sigma Modulator for FPGA-Based All-Digital Transmitters

This paper presents the architecture and implementation of an FPGA-based all digital transmitter with a baseband sampling rate of 1 GHz. Hardware complexity and operation frequency analysis are performed to find the best hardware topology to improve the transmitter performance. The used polyphase decomposition techniques for delta sigma modulators considerably improve the bandwidth and SNR figures of merit of state-of-the-art FPGA integrated RF transmitters. The experimental results obtained show the feasibility of this approach and the improvement in the signal modulator oversampling ratio, enabling higher bandwidth in all-digital transmitters.

All-Digital Transmitter With a Mixed-Domain Combination Filter

In this brief, we present a new reconfigurable filtering technique for all-digital transmitters using signal interference and cancellation. The proposed method allows the change of some filtering characteristics digitally. This technique is used to reduce the quantization noise from the all-digital transmitters output, reducing the analog output filter requirements. Without a narrow band filter, a greater degree of flexibility for the transmitters carrier frequency and bandwidth is attained, improving its suitability for multiband and multistandard operation. The results show the quantization noise reduction without an output analog filter, contributing to an increase of the transmitters coding efficiency up to more than 95%.

Wideband all-digital transmitter based on multicore DSM

This paper presents a new wideband all-digital pulsed transmitter architecture based on delta-sigma modulation. The proposed architecture uses a parallel approach for the signal modulator to augment the digital system sampling frequency. The improvement of the sampling frequency allows to enhancement of the transmitter bandwidth without the need of high speed digital logic for the pulse modulator. The FPGA prototype results show the feasibility and advantages of the proposed architecture in terms of bandwidth. The measurements show that the proposed transmitter is capable of a 122 MHz bandwidth signal transmission, which represents a significant improvement over the current state-of-the-art bandwidth for all-digital pulse transmitters.

A Broadband Almost-Digital RF Transmitter With an Efficient Power Amplifier

A new architecture of an almost-digital RF transmitter is proposed. It consists of easy-to-have functional modules. Among the modules, a broadband Doherty amplifier is focused through a modified design approach. A proof-of-concept transmitter is built and measured. It demonstrates quite comparable performances: more than 40% of power-amplifier efficiency, adjacent channel leakage ratios between -26 and -37 dB, and average 2.6% of error vector magnitude over a frequency band from 0.7 to 1.1 GHz, which corresponds to a fractional bandwidth of 44%, when it is driven by a signal with 5.6 dB of peak-to-average power ratio.

All-digital transmitter with RoF remote radio head

This paper presents a new radio-over-fiber system that uses an all-digital transmitter architecture enabling a very simple remote radio head comprised only by an amplifying stage, a bandpass filter and an antenna. An all-digital transmitter is proposed to implement a flexible centralized digital radio, able to perform the baseband processing and transmission of radio signals at radio frequencies (RF) over an optical fiber. The digital signal at RF is transmitted over fiber using a simple on-off digital modulation, reducing the limitations of conventional analog radio-over-fiber systems, but maintaining the advantages of a reduced complexity transmitter radio head.

Tunable delta-sigma modulator for agile all-digital transmitters

Fully digital transmitters have been thoroughly explored over the last few years to develop a novel type of agile, reconfigurable, multi-band, multi-standard and highly-efficient transmitters. However, with regard to agility and reconfigurability, current state-of-the-art approaches are still very restrictive. This paper proposes a new architecture based on a tunable delta-sigma modulator suitable for designing RF fully digital transmitters either in single-carrier or in dual-carrier scenarios. A 2-path polyphase decomposition was also developed to optimize some figures of merit, such as SNR and EVM, and to demonstrate the scalability of this type of modulator. This novel architecture has been successfully implemented and validated on an FPGA-based transmitter for single- and dual-carrier scenarios.

Agile Single- and Dual-Band All-Digital Transmitter Based on a Precompensated Tunable Delta–Sigma Modulator

In this paper, a new architecture for designing tunable single- and dual-band radio-frequency fully digital transmitters is proposed and validated. The proposed architecture excels the state of the art in terms of simplicity and flexibility. While its short critical path leverages the use of equivalent polyphase decomposition techniques to increase the global systems sampling frequency, the capability of changing the systems frequency response in real time enables its use in both single- and dual-band transmission scenarios. To mitigate a crosstalk in the dual-band scenario, a precompensation technique is also proposed. This novel concept has been successfully validated in a field-programmable gate array (FPGA) based transmitter. To validate both the proposed transmitter as well as the precompensation mechanism, spectrum and error-vector magnitude (EVM) measurements were obtained for two scenarios with a carrier frequency of 2.5 GHz: 1) single-band, using quadrature phase-shifting keying (QPSK), 16-quadrature amplitude modulation (QAM) and 64-QAM, with no intermediate frequency (IF), for different symbol rate (SR) values (from 3.125 up to 15.625 Msps) and 2) single- and dual-band, using QPSK and 16-QAM, with an SR of 3.125 Msps, for different IF values (from 2 up to 120 MHz). All the experimental results present EVM values below 2.6%, resulting in a well-defined constellation.

FPGA-based all-digital software defined radio system demonstration

All-digital radios allow the full digitalization of the radio system which poses an important step towards the complete software description of RF signals proposed in SDR. Using digital signal processing techniques and the integration of the radio into a single digital chip, it is expected that high flexibility in these systems will be fundamental for the next generation of wireless networks. In addition, FPGA-based architectures take advantage of the high and heterogeneous processing power of modern FPGAs as well as their dynamic configurability capabilities needed for highly flexible radio transceivers.

Agile All-Digital RF Transceiver Implemented in FPGA

This paper presents a new all-digital transceiver architecture fully integrated into a single field-programmable gate array chip. Both the radio frequency (RF) receiver and the transmitter were entirely implemented using a digital datapath from the baseband up to the RF stage without the use of conventional analog-to-digital converter, digital-to-analog converter, or analog mixer. The transmitter chain uses delta-sigma modulation and digital upconversion to produce a two-level RF output signal. The receiver uses a high-speed comparator and pulsewidth modulation to convert the RF signal into a single-bit data stream, which is digitally filtered and then downconverted. Both the transmitter and the receiver are agile with flexible carrier frequency, bandwidth, and modulation capabilities. The transceiver error vector magnitude and the signal-to-noise ratio figures of merit were analyzed in a point-to-point transmission to evaluate the transmitter’s performance. The results show the feasibility of this approach as a more flexible alternative to common radio architectures.

Relaxing all-digital transmitter filtering requirements through improved PWM waveforms

This paper presents a new pulse-width modulation (PWM) technique for all-digital transmitters (ADT) that reduces the PWM harmonic distortion near the transmitted carrier frequency. This technique is used to shape the ADTs quantization noise by changing the PWM waveform patterns, avoiding the need of a high quality factor analog output filter. With this approach, the ADT gains an additional degree of flexibility for the carrier frequency since it is not bound to any fixed narrow-band filter. The results show the feasibility and advantages of the approach without increasing the complexity for the overall system. The noise peak power reduction shown is quite significant, reaching more than 50 dB reduction for the first PWM harmonic.