Base Band Research Articles

A 2.4 GHz ZigBee Receiver Exploiting an RF-to-BB-Current-Reuse Blixer + Hybrid Filter Topology in 65 nm CMOS

A 2.4 GHz ZigBee receiver unifying a balun-LNA-I/Q-mixer (Blixer) and a baseband (BB) hybrid filter in one cell is fabricated in 65 nm CMOS. Without any external components, wideband input matching and passive pre-gain are concurrently achieved via co-optimizing an integrated low-Q network with a balun-LNA. The latter also features active-gain boosting and partial-noise canceling to enhance the gain and noise figure (NF). Above the balun-LNA are I/Q double-balanced mixers driven by a 4-phase 25% LO for downconversion and gain-phase balancing. The generated BB currents are immediately filtered by an IF-noise-shaping current-mode Biquad and a complex-pole load, offering first-order image rejection and third-order channel selection directly atop the Blixer. Together with other BB and LO circuitries, the receiver measures 8.5 dB NF, 57 dB gain and $-$ 6-dBm IIP3 $_{{\rm out}\mathchar702D{\rm band}}$ at 1.7 mW power and 0.24 mm $^{2}$ die size. The S $_{11}$ -bandwidth ( ${ 10 dB) covers 2.25 to 3.55 GHz being robust to packaging variations. Most performance metrics compare favorably with the state-of-the-art.

Simultaneous Generation of Independent Wired and Wireless Signals Using a Dual-Electrode MZM in ROF System

In this paper, a novel Radio-over-Fiber scheme to simultaneously generate and transmit baseband (BB) and millimeter-wave (MMW) signal by using a single dual-electrode MZM is proposed. By employing this analog ROF signal transmission techniques, highly transparent fiber-wireless networks, which are ideal for multi-standard wireless system operation can be realized.

L, C and X band integrated synthetic aperture radar (SAR) receiver

An integrated receiver consisting of RF front ends, analog baseband (BB) chain with an analog to digital converter (ADC) for a synthetic aperture radar (SAR) implemented in 130 nm CMOS technology i...

A 10-Bit 2-GS/s DAC-DDFS-IQ-Controller Baseband Enabling a Self-Healing 60-GHz Radio-on-Chip

A 10-bit 2-GS/s mixed-signal baseband (BB) circuit, which enables a self-healing 60-GHz 4-Gb/s radio-on-chip implemented in a 65-nm complementary metal-oxide semiconductor, is described. The BB circuit autonomously senses and optimizes transmitter (TX) P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1dB</sub> , OIM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> , and image suppression, reducing the yield loss because of process variations. On-chip test tones are generated using a 10-bit 2-GS/s current-steering digital-to-analog converter (DAC) and direct digital frequency synthesizer (DDFS). Using the generated test tones, the aforementioned impairments are measured by an envelope detector at the power amplifier output. Based on this information, the programmable digital IQ phase amplitude and offset controller (IQ_CTRL) in the BB circuit improves the TX image suppression from -32.4 to -42.6 dBc, and digital control signals generated by the on-chip self-healing controller heal the TX P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1dB</sub> and OIM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> from 9.5 to 13.2 dBm and from -32.5 to - 40 dBc, respectively. In terms of achieving the target specifications, namely, TX image suppression , , and , healing increases yield on ten dies from 0% to 100%. The BB circuit consumes only 49 mW, of which 37 mW comes from the DACs and 12 mW from the DDFS and the IQ_CTRL.

10-Gbit/s Wireless Communication System at 300 GHz

A 10-Gbit/s wireless communication system operating at a carrier frequency of 300 GHz is presented. The modulation scheme is amplitude shift keying in incoherent mode with a high intermediate frequency (IF) of 30 GHz and a bandwidth of 20 GHz for transmitting a 10-Gbit/s baseband (BB) data signal. A single sideband transmission is implemented using a waveguide-tapered 270-GHz highpass filter with a lower sideband rejection of around 60 dB. This paper presents an all-electronic design of a terahertz communication system, including the major modules of the BB and IF band as well as the RF modules. The wireless link shows that, aided by a clock and data recovery circuit, it can receive 2 7 –1 pseudorandom binary sequence data without error at up to 10 Gbit/s for over 1.2 m using collimating lenses, where the transmitted power is 10 μW.

Wireless over cable for femtocell systems

Interference control is crucial to reach the expected spectral efficiencies in femtocell systems. Centralized and joint baseband (BB) processing of all femtocell signals can reduce inter-cell/intra-cell interference at the expense of fast signaling and strict synchronization to coordinate the multiple femtocell links. In this article, we revisit the conventional femtocell architecture by proposing the multi-cell baseband processing for interference mitigation based on a distributed antennas system. The proposed configuration resorts to the wireless over cable (WoC) paradigm and is based on the concept of replacing the in-house base station (Femtocell Access Point) with a home-device that simply transfers the analog radio frequency (RF) signals from the air-link to the existing cable connections. These home-devices act as bidirectional amplify-and-forward (AF) relays of air signals toward cable (and vice-versa) by operating a frequency conversion of the wireless spectrum to accommodate the cable specifications and coexistence with other services. Splitting RF processing (at home) from baseband processing (centralized at the nearest street cabinet or central office collecting multiple cables) guarantees that multi-cell processing exploits the same advantages as MIMO systems. The analysis of WoC for twisted pair telephone lines shows the advantages of the FemtoWoC architecture despite the coexistence with other interfering xDSL services over the cable, or the propagation over the widely deployed copper wirelines.

An Intuitive Current-Driven Passive Mixer Model Based on Switched-Capacitor Theory

An intuitive current-driven passive mixer model is presented. Without using complex math, it provides a signal-transfer-function/noise description of a passive mixer when used in a wireless receiver (RX) chain driven by a transconductor and loaded by a low-pass baseband (BB). Exploiting a switched-capacitor approach, the model represents a useful tool for simple hand analysis and design. The case of a 25 $ \%$ -duty-cycle quadrature RX chain based on a transimpedance amplifier at BB is analyzed in detail and compared with simulations, showing good accuracy.

Generation and Transmission of BB/MW/MMW Signals by Cascading PM and MZM

A bidirectional three-band lightwave transport system is proposed and experimentally demonstrated for both fiber-to-the-X (FTTX) and radio-over-fiber (RoF) networks. By cascading a phase modulator (PM) and a Mach-Zehnder modulator (MZM) to generate multiple coherent lightwaves, hybrid 1.25 Gbps baseband (BB), 1.25 Gbps/20 GHz microwave (MW), and 1.25 Gbps/40 GHz millimeter-wave (MMW) downstream signals and a 1.25 Gbps BB upstream signal are simultaneously transmitted. Furthermore, with an assistance of an optical signal-to-noise ratio (OSNR) enhancement circuit, sufficient low bit error rate (BER) values are experimentally achieved for both down-link BB/MW/MMW and up-link BB signals. No additional high-frequency local oscillator, mixers and upstream laser diode are required in both transmitter and receiver sites. Under this architecture, both wire-lined and wireless clients can be simultaneously served without using any extra device/equipment to convert the downstream signals among BB, MW and MMW formats.

A Four-Antenna 802.11a Receiver integrated in 0.25 µm SiGe BiCMOS with Spatial Weighting

This paper presents the design and results of a four-antenna integrated receiver (RX) frontend in 0.25 µm SiGe BiCMOS. It performs antenna combining in the radio-frequency (RF) domain with IEEE 802.11a compliant signals. Therefore, the RF part of this integrated circuit (IC) includes four low noise amplifiers (LNAs), vector modulators (VMs) and a signal combiner. These circuits can weight the incoming C-band (5.6 GHz) signals in their I- and Q-components with an 8-bit resolution before superposition and downcoversion. The baseband (BB) part of the applied zero-IF architecture integrates an 8th order switched-capacitor (SC) filter for channel selection and variable gain amplifiers (VGAs) for automatic gain control (AGC). Together with digital control logic the power consumption amounts to 350 mW at an area requirement of 7.5 mm2.

Experimental study of coexistence of multi-band OFDM-UWB and OFDM-baseband signals in long-reach PONs using directly modulated lasers

Transmission of coexisting Orthogonal Frequency Division Multiplexing (OFDM)-baseband (BB) and multi-band OFDM-ultra-wideband (UWB) signals along long-reach passive optical networks using directly modulated lasers (DML) is experimentally demonstrated.When optimized modulation indexes are used, bit error ratios not exceeding 5 × 10⁻⁴ can be achieved by all (OFDM-BB and three OFDM-UWB sub-bands) signals for a reach of 100 km of standard single-mode fiber (SSMF) and optical signal-to-noise ratios not lower than 25dB@0.1 nm. It is experimentally shown that, for the SSMF reach of 100km, the optimized performance of coexisting OFDM-BB and OFDM-UWB signals is mainly imposed by the combination of two effects: the SSMF dispersion-induced nonlinear distortion of the OFDM-UWB signals caused by the OFDM-BB and OFDM-UWB signals, and the further degradation of the OFDM-UWB signals with higher frequency, due to the reduced DML bandwidth.

Novel ROF/FTTX/CATV hybrid three-band transport system

A novel cost-effective radio-over-fiber (ROF)/fiber-to-the-X (FTTX)/CATV hybrid three-band transport system based on direct modulation of a distributed feedback laser diode (DFB LD) with multi-wavelength output characteristic is proposed and experimentally demonstrated. Radio-frequency (RF) (1.25 Gbps/6 GHz) signal with direct modulation, as well as baseband (BB) (622 Mbps) and CATV (channels 2-78) signals with external remodulation are successfully transmitted simultaneously. Low bit error rate (BER) and clear eye diagram were achieved for ROF and FTTX applications; as well as good performances of carrier-to-noise ratio (CNR), composite second-order (CSO) and composite triple beat (CTB) were obtained for CATV signals over an 80-km single-mode fiber (SMF) transport.

Digital processing compensation mechanisms for highly efficient transmitter architectures

This article presents the design and final field programmable gate array (FPGA) integration of the necessary baseband (BB) signal processing for some of the emergent highly efficient amplification architectures. Following the software-design radio concept, this design is aimed at generating, monitoring and correcting BB and intermediate frequency signals for operating in highly efficient power amplifier (PA) architectures, such as envelope tracking PAs, envelope elimination and restoration or polar transmitter and linear amplification with non-linear components. The closed-loop nature of this FPGA design allows introducing control strategies to overcome or mitigate the unwanted distortion arising from maladjustments in the aforementioned efficient transmitter architectures. In addition to the signal generation blocks, three key blocks are included in the design to significantly contribute to the performance of these power-efficient architectures. These three blocks are a fractional delay filter block, a block that generates a slower (or slew-rate-limited) version of the envelope of the signal and a digital adaptive predistortion block. Experimental results presented in this article show the importance of including these blocks to provide these efficient transmitter architectures with correcting capabilities to guarantee power efficiency and linear amplification at RF.

Gigabit-converged wired and wireless networks for simultaneous multi-services transmission

A novel architecture of converged radio-over-fiber (RoF) and wavelength division multiplexed passive optical network (WDM-PON) system, namely RoF-WDM-PON, is demonstrated. 20-GHz 1-Gb/s radio frequency (RF) signals and 1-Gb/s baseband (BB) signals are simultaneously generated and transmitted using optical carrier suppression (OCS) modulation techniques. The proposed scheme is compatible with the conventional RoF and PON system. 25-km single-mode fiber (SMF) transmission is successfully achieved.

Simultaneous Generation and Transmission of 60-GHz Wireless and Baseband Wireline Signals With Uplink Transmission Using an RSOA

This study presents a novel hybrid access network for 60-GHz wireless and wireline applications using a frequency quadrupling technique. Both 1.2-Gb/s eight phase-shift keying and 1.25-Gb/s quadruple phase-shift keying radio-frequency (RF) signals for radio-over-fiber (RoF) links are demonstrated. A 1.25-Gb/s baseband (BB) on-off keying (OOK) signal for fiber-to-the- x services is simultaneously generated and transmitted using the same modulator. The proposed system does not suffer from RF fading and needs no narrowband optical filter at the remote node to separate the RF and BB signals. A frequency quadrupling method for RoF link is realized to reduce the bandwidth requirement of the transmitter. Following 25-km single-mode fiber transmission, the observed receiving power penalty is negligible for both RF and BB signals. Wavelength reuse for a 1.25-Gb/s OOK signal via a reflective semiconductor optical amplifier for uplink transmission is also demonstrated.

Co-Channel Interference Cancellation Using Single Radio Frequency and Baseband Chain

We present a new architecture for multi-antenna receivers that cancels the co-channel interference (CCI) using a single radio frequency (RF) and baseband (BB) chain, while still achieving nearly the same bit error rate that can be provided by the conventional receiver architecture requiring multiple RF/BB chains. The proposed receiver architecture enables multiple transmitter-receiver pairs to simultaneously communicate in the same frequency band without additional bandwidth, thereby increasing the spectral efficiency or capacity, with significantly reduced receiver complexity and power consumption.

Transmission of Wireless and Wired Services Employing a Simple System Architecture

This letter presents a novel modulation approach for simultaneous generation and transmission of optical radio-frequency (RF) wireless vector signal and baseband (BB) wireline signal using a single-electrode Mach-Zehnder modulator. Based on a double sideband with carrier suppression scheme and properly predistorted driving vector signal, a 2.5-Gb/s quadrature phase-shift keying (QPSK) signal at 60 GHz is generated with a 1.25-Gb/s BB ON-OFF-keying (OOK) signal. The proposed system can carry higher spectral efficiency vector signals and needs no optical filter to separate the BB and RF signals at remote nodes. Moreover, optical RF signal generation with frequency doubling is also achieved to reduce the bandwidth requirement of the transmitter. After transmission over 25-km single-mode fiber, the power penalties of the generated QPSK and OOK signals are about 4 and 0.1 dB, respectively.

A broadband ASE light source-based full-duplex FTTX/ROF transport system

A full-duplex fiber-to-the-X (FTTX)/radio-over-fiber (ROF) transport system based on a broadband amplified spontaneous emission (ASE) light source is proposed and demonstrated for rural wide-spread villages. Combining the concepts of long-transmission transmission and ring topology, a long-haul single-mode fiber (SMF) trunk is sharing with multiple rural villages. Externally modulated baseband (BB) (1.25 Gbps) and radio-frequency (RF) (622 Mbps/10 GHz) signals are successfully transmitted simultaneously. Good bit error rate (BER) performance was achieved to demonstrate the practice of providing wire/wireless connections for long-haul wide-spread rural villages. Since our proposed system uses only a broadband ASE light source to achieve multi-wavelengths transmissions, it also reveals an outstanding one with simpler and more economic advantages.

Simultaneous Transmission of Millimeter-Wave and Baseband Signals Using Wavelength Interleaving and Polarization Multiplexing for an Integrated Reconfigurable Access Network

A novel scheme for the simultaneous transmission of 1.25-Gb/s baseband (BB) signals and 155-Mb/s 60-GHz radio-over-fiber (RoF) signals is experimentally demonstrated. The BB and RoF signals are wavelength-interleaved and polarization multiplexed. Tunable filtering along with polarization demultiplexing are used to drop an RoF signal with the wavelength-interleaved BB signal. This scheme is suited for future reconfigurable ring/bus access networks to provide an integrated platform for BB and millimeter-wave services.

Hybrid Access Network Integrated With Wireless Multilevel Vector and Wired Baseband Signals Using Frequency Doubling and No Optical Filtering

This letter experimentally demonstrated a hybrid access network which supports both radio-over-fiber and fiber-to-the-x systems. A 20-GHz radio-frequency (RF) 312.5-MSymbol/s M-ary phase-shift keying (PSK) signal and a baseband (BB) 1.25-Gb/s on-off keying signal are simultaneously generated and transmitted over an identical distributed infrastructure. The wired BB signal is compatible with the existing passive optical network (PON) system, and the wireless RF PSK signal can also share the same distributed infrastructure. The proposed system has no RF fading issue, no narrowband optical filter at remote node to separate the RF and BB signals, and can carry vector signals. Moreover, a frequency doubling for optical RF signal generation is achieved to reduce the bandwidth requirement of the transmitter. After transmission over 25-km standard signal-mode fiber, the receiver sensitivity penalties are less than 0.5 dB for both the RF and BB channels.

Implementation of a [formula omitted] MIMO-OFDM receiver on an application specific processor

This paper describes the implementation of the hard computational kernels required for the baseband (BB) processing of a 2×2 multiple-input multiple-output (MIMO)-OFDM receiver on a design-framework for application specific processors. The employed low-complexity BB algorithms are described and their computational complexity is derived. The receiver is split into two parts which are mapped onto two application specific processors, each tailored to the computational needs of the associated digital signal processing kernels. The first processor performs the per stream MIMO-OFDM processing. The second processor handles the MIMO detection. Finally, the 0.18μm 1P/6M CMOS technology layout of both fabricated application specific processors is presented. Real-time BB processing is possible on these engines running at a clock frequency of 250MHz.