Spur-free Dynamic Range Research Articles

Calibration‐spur reduction in current‐steering DAC utilising digital‐and‐analogue hybrid return‐to‐zero (HRZ) method

A simple-but-efficient calibration-spur reduction technique is introduced that utilises the digital-and-analogue hybrid return-to-zero (HRZ) method in a current-steering DAC employing a round-robin-fashioned background current-source calibration scheme. A simulation with a 12 b 500 MS/s current-steering DAC showed 9.9 and 7.8 dB improvements in the spur-free dynamic range and signal-to-noise + distortion ratio, respectively, owing to the reduced calibration spur by the proposed HRZ technique.

150–850 MHz High-Linearity Sine-wave Synthesizer Architecture Based on FIR Filter Approach and SFDR Optimization

A low distortion sinusoidal waveform synthesizer architecture is proposed. The synthesizer utilizes 50% duty cycle and differential-mode circuitry to eliminate the even order harmonics, and it also implements a 5-phase 3-amplitude harmonic cancellation technique to suppress the 3rd, 5th, 7th, and 9th order harmonics. The compact system architecture consists of a 12-phase ring oscillator, a weighted resistor summing network, and an RC output filter. Phase shifters are adopted in the ring oscillator to enable the control of an external harmonic cancellation optimization algorithm. The proposed application of the optimization algorithm compensates the errors in the circuit and further improves the linearity of the output waveforms. This synthesizer is fabricated in 180 nm standard CMOS technology, occupies a 0.08 ${\rm mm}^{2}$ silicon area and achieves the spur-free dynamic range (SFDR) of 59 to 70 dBc from 150 to 850 MHz after the optimization procedure. It can operate from a 1 to 1.8 V supply voltage and achieve a power consumption from 9.11 to 57 mW.

RF Performance of Single Sideband Modulation Versus Dual Sideband Modulation in a Photonic Link

Single sideband optical modulation can be used in multiple RF photonic link applications. However, single sideband optical modulation is often thought to provide lower RF output power than traditional dual sideband modulation techniques. While true in one specific case, it is not true in all cases. We theoretically and experimentally analyze the RF performance of a photonic link utilizing a Z-cut dual-electrode Mach-Zehnder intensity modulator with a 90° RF hybrid that produces optical single sideband modulation. The single sideband performance is compared to double sideband modulation using the same Mach-Zehnder modulator in either a push-pull configuration using a 180° RF hybrid or a single-arm drive configuration. The optical sideband powers, RF output power and the output intercept power and spur-free dynamic range of the third-order intermodulation nonlinearity are compared both theoretically and experimentally for each of the three cases. The performance of a double sideband modulated link using an X-cut inherently push-pull Mach-Zehnder modulator is also compared theoretically, assuming the same V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">π</sub> and insertion loss as the dual-electrode Mach-Zehnder modulator.

A Transmission Model of Analog Signals in Photonic Links

We investigate the transmission of analog photonic signals based on coupled-mode theory and small-signal analysis and provide general expressions for signal evolution along standard single-mode-fiber links. Such model consists of a set of terms that correspond to polarization effects, chromatic dispersion (CD), and fiber nonlinearity. Based on the proposed complete model, we further investigate two typical cases, including the interaction between polarization effects and CD, as well as CD and Kerr effects. In addition, the limitations of the noise figure and spur-free dynamic range are investigated in dispersive nonlinear links.

Linearization Technologies for Broadband Radio-Over-Fiber Transmission Systems

Linearization technologies that can be used for linearizing RoF transmission are reviewed. Three main linearization methods, i.e. electrical analog linearization, optical linearization, and electrical digital linearization are presented and compared. Analog linearization can be achieved using analog predistortion circuits, and can be used for suppression of odd order nonlinear distortion components, such as third and fifth order. Optical linearization includes mixed-polarization, dual-wavelength, optical channelization and the others, implemented in optical domain, to suppress both even and odd order nonlinear distortion components, such as second and third order. Digital predistortion has been a widely used linearization method for RF power amplifiers. However, digital linearization that requires analog to digital converter is severely limited to hundreds of MHz bandwidth. Instead, analog and optical linearization provide broadband linearization with up to tens of GHz. Therefore, for broadband radio over fiber transmission that can be used for future broadband cloud radio access networks, analog and optical linearization are more appropriate than digital linearization. Generally speaking, both analog and optical linearization are able to improve spur-free dynamic range greater than 10 dB over tens of GHz. In order for current digital linearization to be used for broadband radio over fiber transmission, the reduced linearization complexity and increased linearization bandwidth are required. Moreover, some digital linearization methods in which the complexity can be reduced, such as Hammerstein type, may be more promising and require further investigation.

High-Gain, Low-Noise-Figure, and High-Linearity Analog Photonic Link Based on a High-Performance Photodetector

We report a high-gain, low-noise-figure, and high-linearity analog photonic link. The link combines a high-power and low-noise fiber laser, a Mach-Zehnder modulator, a high-gain erbium-doped fiber amplifier (EDFA), and a high-performance charge-compensated modified unitraveling-carrier photodiode. The critical characteristics of the photodiode include 16-GHz bandwidth, 200-mA saturation current, and >35 dBm third-order intercept point. In the link, low biasing is utilized to reduce the noise and maximize the signal-to-noise ratio, and an EDFA is used to provide sufficient optical input to the MUTC photodiode to ensure that the link can achieve high gain and high output RF power. The combination of high-power low-noise fiber laser and high-bandwidth high-power photodiode, we have enabled high gain (27.8 dB at 6 GHz and 24.5 dB at 12 GHz), low noise figure (4.7 dB at 6 GHz and 6.9 dB at 12 GHz), and high spur free dynamic range (>120 dB · Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2/3</sup> ) in the frequency range 6-12 GHz.

A Linearized Intensity Modulator for Photonic Analog-to-Digital Conversion Using an Injection-Locked Mode-Locked Laser

A linearized intensity modulator for pulsed light based on an injection-locked mode-locked laser (MLL) is presented here. This has been realized by introducing a monolithic Fabry–Perot MLL into one of the arms of a conventional Mach–Zehnder interferometer (MZI) and injection-locking it to a MLL which is the input to the interferometer. By modulating the current on the gain section or the voltage of the saturable absorber (SA) section of the injection-locked laser, one can introduce an arcsine phase response on each of the injected longitudinal modes. By combining the modulated optical comb with its unmodulated counterpart one can produce a linearized intensity modulator. The linearity of this modulator is inherent in its design and no pre- or postdistortion linearization scheme is utilized. The results of the two-tone intermodulation experiment are presented here for this modulator and a spur-free dynamic range (SFDR) of ∼70 dB·Hz2/3 is achieved by modulating the voltage of the SA. The reported SFDR is limited by the noise of the MLLs. The dynamic range could be further improved by decoupling the phase modulation and amplitude modulation. The proposed and demonstrated configuration as an analog optical link with improved linearity has the potential to increase the performance and resolution of photonic analog-to-digital converters (ADCs).

A 5 Giga Samples Per Second 8-Bit Analog to Digital Printed Circuit Board for Radio Astronomy

We have designed, manufactured, and characterized an 8-bit 5 Giga samples per second (Gsps) ADC printed circuit board assembly (PCBA). An e2v EV8AQ160 ADC chip was used in the design and the board is plug compatible with the field programmable gate array (FPGA) board developed by the Collaboration for Astronomy Signal Processing and Electronics Research (CASPER) community. Astronomical interference fringes were demonstrated across a single baseline pair of antennas using two ADC boards on the Yuan Tseh Lee Array for Microwave Background Anisotropy (AMiBA) telescope. Several radio interferometers are using this board for bandwidth expansion, such as Submillimeter Array; also, several experimental telescopes are building new spectrometers using the same board. The ADC boards were attached directly to the Reconfigurable Open Architecture Computing Hardware (ROACH-2) FPGA board for processing of the digital output signals. This ADC board provides the capability of digitizing radio frequency signals from DC to 2 GHz (3 dB bandwidth), and to an extended bandwidth of 2.5 GHz (5 dB) with derated performance. The following worst-case performance parameters were obtained over 2 GHz: spur free dynamic range (SFDR) of 44 dB, signal-to-noise and distortion (SINAD) of 35 dB, and effective number of bits (ENOB) of 5.5.

Optical under-sampling by using a broadband optical comb with a high average power.

We demonstrate a new method to improve the performance of photonic assisted analog to digital converters (ADCs) that are based on frequency down-conversion obtained by optical under-sampling. The under-sampling is performed by multiplying the radio frequency signal by ultra-low jitter broadband phase-locked optical comb. The comb wave intensity has a smooth periodic function in the time domain rather than a train of short pulses that is currently used in most photonic assisted ADCs. Hence, the signal energy at the photo-detector output can be increased and the signal to noise ratio of the system might be improved without decreasing its bandwidth. We have experimentally demonstrated a system for electro-optical under-sampling with a 6-dB bandwidth of 38.5 GHz and a spur free dynamic range of 99 dB/Hz(2/3) for a signal with a carrier frequency of 35.8 GHz, compared with 94 dB/Hz(2/3) for a signal at 6.2 GHz that was obtained in the same system when a pulsed optical source was used. The optical comb was generated by mixing signals from two dielectric resonator oscillators in a Mach-Zehnder modulator. The comb spacing is equal to 4 GHz and its bandwidth was greater than 48 GHz. The temporal jitter of the comb measured by integrating the phase noise in a frequency region of 10 kHz to 10 MHz around comb frequencies of 16 and 20 GHz was only about 15 and 11 fs, respectively.

A 1–6 GHz analog radio frequency power driver in 90 nm complementary metal‐oxide semiconductor technology for wireless applications

SummaryOne of the most challenging subsystems for integrated radio frequency (RF) complementary metal‐oxide semiconductor (CMOS) solutions is the power amplifier. A 1–6 GHz RF power driver (RFPD) in 90 nm CMOS technology is presented, which receives signals from on‐chip RF signal chain components at −12 dBm power levels and produces a 0 dBm signal to on‐chip or off‐chip 50 Ω loads. A unique unit cell design is developed for the RFPD to offset issues associated with very wide multi‐fingered transistors. The RF driver was fabricated as a stand‐alone sub‐circuit on a 90 nm CMOS die with other sub‐circuits. Experimental tests confirmed that the on‐chip RFPD operates up to 6 GHz and is able to drive 50 Ω loads to the desired 0 dBm power level. Spur free dynamic range exceeded 70 dB. The measured power gain was 11.6 dB at 3 GHz. The measured 1 dB compression point and input third‐order intercept point (IIP3) were −4.7 dBm and −0.5 dBm, respectively. Also, included are modeling, simulation, and measured results addressing issues associated with interfacing the die to a package with pinouts and the package to a printed circuit test fixture. The simulations were made through direct current (DC), alternating current (AC), and transient analysis with Cadence Analog Design Environment. The stability was also verified on the basis of phase margin simulations from extracted circuit net‐lists. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Error code correction for phase‐shifted optical quantisation based on maximum likelihood estimation algorithm

An improved error code correction algorithm for phase-shifted optical quantisation is presented and experimentally demonstrated. The error probabilities for each valid code are calculated and the invalid codes are corrected by using the maximum likelihood estimation algorithm. The experimental result shows that the spur-free dynamic range of the system has an improvement of 2.28 dB compared to the Hamming algorithm in a 10-GSamples/s, 4-bit resolution all-optical analogue-to-digital converter.

Experimental evaluation of resolution enhancement of a phase-shifted all optical analog-to-digital converter using an electrical analog-to-digital converter array

A resolution-improvement scheme of a phase-shifted analog-to-digital converter (ADC) is presented and experimentally demonstrated. To improve resolution via the scheme, the optical output of each quantization channel is quantized by an electrical ADC with multiple thresholds instead of a comparator. A 9.9-GHz sinusoidal analog signal is sampled and quantized using the proposed enhancement scheme. The effective number of bits of 4.31 and the spur-free dynamic range of 40.89 dB are obtained, thus indicating an improvement of 0.66 bits and 7.47 dB, respectively.

Analog Signal Transmission in a High-Contrast-Gratings-Based Hollow-Core-Waveguide

In this paper, the performance of an on-chip hollow-core-waveguide (HW) using high-contrast gratings (HCG) for analog signal transmission is analyzed numerically. Simulation results indicate that after propagating 100 m in a HCG-HW with optimally designed parameters, there is very little degradation of either third-order intermodulation distortion spur-free dynamic range (IM3 SFDR) or third-order harmonic distortion (THD) SFDR. Due to the chromatic dispersion of the HCG-HW, the highest second-order harmonic distortion (SHD) SFDR is limited to 107.3 dB · Hz1 / 2. In addition, >; 100 dB · Hz 2/3 IM3 SFDR can be achieved over a radio frequency (RF) range of 80 GHz and an optical wavelength bandwidth of 50 nm after propagation 100 m through a HCG-HW. The parameter dependence of the waveguide performance is also investigated. With a ± 20 nm variation on all parameters, the propagation length in an HCG-HW is limited to ~ 6 m in order to maintain an IM3 SFDR of >; 100 dB · Hz 2 / 3.

A low-power low-voltage slew-rate enhancement circuit for two-stage operational amplifiers

A novel circuit is presented in order to enhance the slew rate of two-stage operational amplifiers. The enhancer utilizes the class-AB input stage to improve current efficiency, while it works on an open loop with regard to the enhanced amplifier so that it has no effect on the stability of the amplifier. During the slewing period, the enhancer detects input differential voltage of the amplifier, and produces external enhancement currents for the amplifier, driving load capacitors to charge/discharge faster. Simulation results show that, for a large input step, the enhancer reduces settling time by nearly 50%. When the circuit is employed in a sample-and-hold circuit, it greatly improves the spur-free dynamic range by 44.6 dB and the total harmonic distortion by 43.9 dB. The proposed circuit is very suitable to operate under a low voltage (1.2 V or below) with a standby current of 200 μA.

Overcoming Chromatic-Dispersion-Induced Power Fading in ROF Links Employing Parallel Modulators

This letter presents a chromatic dispersion (CD) compensation scheme using parallel electro-optic phase and intensity modulators suitable for long-reach radio-over-fiber links. By properly adjusting the optical power and the time delay between the two modulated signals, the power fading aroused by the CD is adequately compensated over a wide operating bandwidth of 0-18 GHz over a 34-km single-mode fiber (SMF). Compared with a double sideband (DSB) modulated link, an enhancement of up to 31 dB·Hz2/3 in the spur-free dynamic range for a 9.5-GHz signal is obtained. Furthermore, a bit-error rate of 10-10 is obtained when a 9.5-GHz carrier loading 2-Gb/s pseudorandom bit sequence is transmitted over the dispersive link, which is not achievable for the DSB modulated link.

Dynamically induced nonlinearity in a resonant-cavity interferometric intensity modulator

The frequency dependence of the spur-free dynamic range (SFDR) in a modulator based on an injection-locked laser is analyzed. It is shown that as the modulation frequency approaches half of the locking range, the SFDR of the modulator approaches that of a standard Mach-Zehnder configuration. At low frequencies, the SFDR degrades by 2 dB for every octave of frequency increase.

Integrated Multifrequency Recognition and Downconversion Based on Photonics-Assisted Compressive Sampling

On the basis of photonics-assisted compressive sampling (CS), we demonstrate for the first time an integrated system with the capacity of multifrequency recognition and downconversion of intercepted radio frequency (RF) component. Using a single analog-to-digital converter (ADC) with sub-Nyquist analog bandwidth of 826.75 MHz, a multicomponent signal with unknown frequencies ranging from 15 to 20 GHz is precisely located with maximum detection error of 100 kHz. The system's ability of photonic downconversion of identified RF component is characterized in terms of spur-free dynamic range (SFDR) as well.

Spur Free Dynamic Range Prediction for Phased Array Receivers

Analytical techniques to determine the linearity and spur-free dynamic range (SFDR) for phased array receivers are presented. The proposed method eliminates the need for circuit-level simulation of intermodulation distortion in an N-element receiver by characterizing the array SFDR from the SFDR for a single receive channel. The analysis separates the relative impact of array factor, circuit architecture and channel linearity to assess the spatial sensitivity of the receiver to jamming signals. The proposed techniques are applied to a comparison of RF phase-shifting and LO phase-shifting receivers. RF phase-shifting architectures are shown to offer more uniform jammer rejection over the beam-scanning range given the same receiver linearity constraints.

Polarization-modulated analog photonic link with compensation of the dispersion-induced power fading

A novel integrable modulator consisting of a polarization modulator and a polarizer is proposed for constructing a high-performance analog photonic link. By adjusting a polarization controller placed before the modulator, both amplitude modulation and phase modulation with adjustable ratio between them are implemented. This feature is used to shift the peak of the frequency response of a dispersive link to any desired frequency, so the dispersion-induced power fading around the frequency is compensated. A proof-of-concept experiment is performed. The compensation of the dispersion-induced power fading in the proposed analog photonic link increases the spur-free dynamic range as large as 12.5 dB.

Design and Implementation of Software-Defined Radio Receiver Based on Blind Nonlinear System Identification and Compensation

As the commonly used wideband software radio receiver does not possess the performance of a high linear dynamic range under multiple signal excitation, a new type of adaptive wideband digital receiver architecture is proposed and designed based on blind nonlinear system identification. The traditional narrowband linear receiving and channelizing technologies should not be applied to deal with the complicated multiple-signal excitation with unknown or time-varying characteristics of time domain or frequency domain. Here, the harmonic and the intermodulation components brought about by the wideband digital receiver are firstly identified and extracted in the frequency domain, then a blind identification criterion for minimizing the short-time energy of the nonlinear components is designed, and the steepest descent method (SDM) or the recursive least square (RLS) algorithm is applied to extract and update iteratively the parameters of the nonlinear behavior model of the wideband digital receiver. Finally, the updated model is utilized to compensate the nonlinear distortion of the receiver in real time. The experimental results show that the spur-free dynamic range (SFDR) of the blind identification digital receiver achieves about 20-dB higher than that of the traditional receiver under multitone or 16-QAM bandpass signal excitation. As regards the large bandwidth and the high power efficiency of the RF front end and ADC circuits, the blind identification receiver architecture is helpful for detecting weak signal in concomitance with in-band or out-of-band strong jammers.