A High-Performance Sigma-Delta Modulator in 0.18μm CMOS Technology

Sigma-Delta (∑∆) modulators are commonly used in high-resolution analog-to-digital converters (ADCs). In this paper, a high-performance modulator targeted for ultra-high-frequency (UHF) radio-frequency identification (RFID) zero-intermediate frequency (ZIF) receivers is designed in standard 0.18μm CMOS technology. The modulator has been designed with switched-capacitor (SC) integrators employing gain-boosted operational amplifiers, voltage comparators and nonoverlapping clock generators to satisfy such requirements as high gain, low voltage and wide bandwidth. The behavioral-level modeling and circuit-level design are carried out with MATLAB/Simulink and Cadence/SpectreRF, respectively. Ultimately, the high-speed and low-power realization of a second-order single-bit modulator with an oversampling ratio (OSR) of 32 is presented. Simulation results shown that, from a 1.8V supply, operated at a sampling frequency of 64MHz, a dynamic range of 53.4dB over a signal bandwidth of 1MHz is achieved.

A bending dipole RFID (Radio Frequency Identification) tag antenna at Ultra High Frequency (UHF) band is presented to meet the requirements of the antenna miniaturization. The overall dimension of the tag antenna is only 55×12 mm2.The input impedance of the antenna is about 43 + j800Ω with Philips EPC UCODE Gen 2 RFID tag microchip. The simulation results show that the designed antenna has a wide impedance bandwidth, covering 840–845MHz and 920–925MHz UHF band, and has a good return loss value and omni-direction, which can meet the practical requirements of RFID tag antenna.

A low power second order hybrid loopfilter Sigma-Delta modulator with high resolution is presented. The structure is composed by a first active integrator followed by a switched-capacitor (SC) integrator. This modulator architecture exploits the coefficient scaling property of the active integrator, while the SC integrator is modified to shift its pole from inside the unit circle to z=1 at DC in the z-domain. Poles of the loopfilter are zeroes of the noise transfer function (NTF). As a result the NTF zero is also shifted to z=1. This NTF zero compensation for the SC integrator will result in better in-band noise suppression & improved noise shaping. The second order hybrid sigma-delta modulator with a 4-bit quantizer and an oversampling ratio (OSR) of 32 is simulated in simulink. The modulator can achieve 89dB SNDR with a dynamic range of 91dB.

In this paper, the simulation of radiation pattern of the proposed RFID C-slot tag antenna on a coated metallic cylindrical surface is presented. It is found that the radiation pattern in the shadow zone (behind the product) from the proposed RFID tag is stronger than that from the electric current source case (electric tag). Thus, the proposed C-slot tag antenna is useful for the RFID application especially for the curved metallic surface product.

By applying information theoretic concepts to analog-to-digital convertor (ADC) design, we have created a mathematical framework from which the fundamental limit for the resolution-bandwidth product of any ADC may be derived. We found the surprising result that the limiting resolution of any ADC is proportional to oversampling-ratio (OSR), as opposed to widely-held belief that the resolution is proportional to \(log_2(OSR)\), a dramatic increase in the achievable resolution. This result, which resembles Shannon’s well-known result for the capacity of a communication channel, represents a paradigm shift in our understanding of data conversion methods and provides encouragement that new methods may be found. Furthermore, to achieve this theoretical limit, the internal analog modulator (or filter) of an ADC should be a chaotic system, so that both small as well as large changes in the input signal cause large (but bounded) deterministic changes at the output of the modulator - analogous to the “Butterfly effect”. This led us to discover a new class of ADCs, which we call TurboADC’s, that can trade off resolution for bandwidth on the fly, keeping their product equal to the fundamental information theoretic limit. These designs impose modest requirements on the analog front-end resources and power at the expense of greater complexity in the back-end decoder. A discrete-time TurboADC proposed here is a hybrid of a 1st order Delta-Sigma modulator and a Cyclic ADC, with the best features of both designs - oversampling, noise shaping, and simplicity from the Sigma-delta ADC approach and fast half-interval searching from Cyclic ADC’s. Simulations of the proposed TurboADC confirm our finding that the resolution of an ADC may approach fundamental limit of OSR bits within the baseband.

Passive UHF (ultra high frequency) RFID (radio frequency identification) is a promising technology for products tracking in logistics or routing packages in supply chain. However, passive UHF RFID tag suffers a lot when it is placed on conductive plane or water surface. Many designs like microstrip antenna and ferrite antenna have been used to solve this metal-water problem. But their use is limited by narrow bandwidth and low antenna gain. The electromagnetic band gap (EBG) material which exhibits a unique forbidden band gap at certain frequency offers a potential solution to solve the problem of backside objects effects. Previous research paper indicated that the dipole RFID antenna above three-layer mushroom like EBG material exhibited a good antenna gain and long read range. However, the complicated structure and high material cost greatly limit the application of tag. In this paper, we developed a new type of EBG material which uses ferrite film to reduce size and lower forbidden frequency. A commercial ferrite film which has a high permeability is applied to form two-layer mushroom like EBG material for UHF RFID. This two-layer mushroom like EBG material is a two-layer structure with a ground plane. The design of EBG material for UHF RFID which operates at 915 MHz was discussed in this paper. An EBG tag on metal with a gain of 7 dBi was achieved in simulation. The simulation results showed that the RFID tag still could be read on EBG substrate with a good gain (~7 dBi).

This paper presents a band-pass noise-shaping (NS) successive-approximation-register (SAR) analog-to-digital converter (ADC) with a second-order modulator which is comprised of a fully passive switched-capacitor (SC) filter and a gain-boosted dynamic amplifier. It employs the error-feedback (EF) structure in a simple method to implement the complicated noise transfer function (NTF) zeros, which enhances the noise-shaping capability by minimally modifying a standard SAR ADC. Designed in 28 nm CMOS process, the prototype of proposed NS-SAR ADC achieves 76.84 dB signal-to-noise and distortion ratio (SNDR) with the bandwidth between 20 and 40 MHz and the FoMw is only 2.24 fJ/step at the oversampling ratio (OSR) of 5.

This paper discusses the fabrication and wireless performance of 3D-printed graphene-based passive UHF (ultra high frequency) RFID (radiofrequency identification) tags on two different cardboard packaging substrates. Our results confirm that the low-cost and eco-friendly graphene-based RFID tags achieve high performance with attainable read ranges of 3.2–3.8 meters. These results are superior to those of previously reported RFID tags with graphene antennas.

ABSTRACTIn this research, two low profile metal mountable patch antenna designs for passive ultra-high frequency (UHF) radio frequency identification (RFID) tag are proposed. The complex impedance matching between the antenna and the referenced microchip, Alien-Higgs 3 whose impedance , is realized through an inductively coupled loop feed structure where it provides the needed reactance for the tag antenna. To enhance the bandwidth of the antenna, multiple co-planar radiating patches are employed to excite several resonant modes for worldwide use. The wide impedance bandwidth also compensates for fabrication inaccuracy which could shift the operating frequency of the final antenna design. The final dimensions of the antennas are 87 × 45 × 1.6 mm3 and 130 × 63 × 1.6 mm3. The measured impedance bandwidths of the proposed antennas when mounted on a metal plate are 155 MHz (RL ≥ 3 dB), which is from 830 to 985 MHz, and 117 MHz (RL ≥ 6 dB), which is from 850 to 967 MHz, respectively. The maximum simulated gains are −7 and −11 dB at the operating frequency of 915 MHz. Based on the measurement results, it is expected that the proposed antenna would be able to provide a reasonable read range of at least 2 m throughout the entire UHF RFID band when being attached on metal objects.

A new fully passive noise-shaping architecture for successive approximation register (SAR) analog-to-digital converters (ADCs) was proposed. A first-order noise transfer function (NTF) with zero located nearly at one can be achieved. The additional pole increases the efficiency of noise shaping to further 3 dB. So, the use of higher over sampling ratios (OSR) and increased effective number of bits (ENOB) is possible. The architecture was applied to the design of a 9.8-bit ENOB SAR ADC in a 65 nm complementary metal-oxide semiconductor (CMOS) of United Microelectronics Corporation (UMC) with OSR equal to 10. A 6-bit capacitive DAC was used. The proposed architecture provides 3.8 additional bits in ENOB. The equalent input bandwitdth is equal to 200 kHz with the sampling rate equal to 4 MS/s.

Oilfield tubulars (typically metallic pipes) and other types of oilfield equipment are typically stored in outdoor areas and may be scattered around the field. Managing these types of inventory is challenging and costly, as it requires significant labor resources. Therefore, inventory inaccuracy is common, and data-driven decisions may not be possible in a timely manner. We propose the use of radio frequency identification (RFID) for tracking oilfield tubulars and similar, outdoor-stored, equipment. Our proposed application utilizes passive ultra-high frequency (UHF) RFID technology that enables capturing unique serial identification numbers that are attached to inventory items from a distance of several meters. Passive UHF RFID tags require no batteries to operate. Typical tag cost is low. Each tag is placed on an inventory item and corresponds to a database entry containing specific information about this item. The tag communicates its serial number using power provided by an RFID reader radio transmission. The RFID reader is securely mounted to the underside of a UAV flown over the field. Captured RFID tags are either stored locally and retrieved once the UAV lands, or are wirelessly transmitted to a constantly updating inventory database. In addition to tag ID, the captured data typically includes time and date stamp, as well as location data. This research project included the design and manufacturing of an enclosure to house a RFID reader system which includes a host computer, embedded reader, antenna, power source, and necessary components for user interface. Specialized mounts were designed and manufactured to attach the enclosure and antenna to the UAV. The project incorporated the development of "middleware", specialized software installed on the host computer to communicate with the reader. The reader handles low-level communication with the antenna. To reduce network traffic, event management and data filtering are efficiently performed. The results of several UAV flights in experimental areas are presented and discussed. Various brands of passive RFID tags for oilfield applications were tested. Particular attention was given to population density of the items, stacking configuration, vertical altitude distance between reader and tags, and time to collect inventory data for a given area of surveillance. As RFID applications are increasing in the oil, gas, solar, and other sectors of the energy production industries, UAVs can effectively be used to get important operational and inventory data. UAV use is particularly appealing in inaccessible and remote locations.

We developed hardware and software to perform exposure studies of the effects of certain radio frequency (RF) electromagnetic fields on solid and liquid pharmaceuticals and biologies. The RF fields generated by our systems are similar to those emitted by radio frequency identification (RFID) readers operating in the USA licensed high frequency (HF) and ultra high frequency (UHF) bands (13.56 and 915 MHz respectively). Our systems can expose drug samples (pharmaceuticals and biologies) to uniform electric (E) and/or magnetic (H) fields at levels that are much higher than those experienced by drugs near "worst-case" readers at a distance of 20 cm. Worst-case readers are defined as those that emit the highest allowable field strengths. Maximum field strengths near these readers were identified by measurements and computations of fields from commercial readers, and are extrapolated to the maximum allowable effective isotropic radiated power or field strength dictated by the U.S. Federal Communications Commission (FCC). The UHF system we developed included a commercially available circularly polarized antenna, a microwave generator with pulse modulation, a high power amplifier, a plastic foam enclosure, and fiber optic temperature monitoring probes placed in the drugs and the surrounding air. The HF system we developed included a specially designed Helmholtz coil pair, an HF signal generator with pulse modulation, an HF amplifier, an RF impedance matching device, and the same enclosure, and thermometry system as in the UHF system. Exposures can be performed for each drug in both its retail primary package (the smallest container produced with an RFID tag on it, e.g. bottle) and in 54 mm diameter culture dishes. The containers are suitable for exposing a wide variety of formulations of drugs (tablets, liquids, powers, capsules, creams, etc.). Exposures of drugs in culture dishes assure uniform induced electric fields and currents. In contrast, exposures in the primary containers (e.g. vials) allow studies that account for the interactions of RF fields with the packaging materials and container geometry. In our UHF system we can expose drugs to over 20 watts effective isotropic radiated power over 5 times the FCC limits. We evaluated H fields emitted by commercially available RFID readers. In our HF system we can expose drugs to at least 5 times the H field they produce at 20 cm from the reader. We can expose samples to 5 A/m in primary packaging or in special organ culture dishes with an outer concentric ring. The ring has inner and outer diameters of 32 mm and 55 mm respectively. Computer monitoring of power, drug temperature, and air temperature can be performed continuously during exposure. Surrounding air temperature is monitored at all times while in our lab (storage and exposure) and while shipped to drug laboratories for analysis.

This work presents a digital calibration technique in continuous-time (CT) ΔΣ analog to digital (A/D) converters. The converter is clocked at 144MHz with a low oversampling ratio (OSR) of only 8. Dynamic element matching (DEM) is not efficient to linearize the digital to analog converter (DAC) when the OSR is very low. Therefore, non-idealities in the outermost multi-bit feedback DAC are measured and then removed in the background by a digital circuit. A third-order, four-bit feedback, single-loop CT ΔΣ converter with digital background calibration circuit has been designed, simulated and implemented in 65nm CMOS process. The maximum simulated signal-to-noise and distortion ratio (SNDR) is 67.1dB within 9MHz bandwidth.

This paper presents a resolution-reconfigurable discrete-time dynamic zoom analog-to-digital converter (ADC) with a 20-kHz bandwidth. It employs a coarse 6-bit successive approximation register (SAR) ADC that dynamically updates the references for the post-stage single-bit second-order delta-sigma modulator to obtain a higher resolution with lower power. The sampling rate of the proposed ADC can be configured to be 1.6, 3.2, 6.4 and 10-MS/s such that four resolution modes, including 12, 14, 16 and 18-bit, can be provided accordingly. Note that pole locations of the noise transfer function (NTF) vary with different OSR's, and noise-shaping effect, together with the power efficiency, can be degraded. To solve this issue, the pole-optimization technique is proposed in this paper. In this way can the pole locations be reconfigured according to the specific OSR. Additionally, the bandwidths of the operational amplifiers are also modulated in different oversampling ratio (OSR) scenarios to further improve the energy efficiency. Fabricated in a 0.18- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> CMOS process, the prototype occupies 1.01 mm2. On condition of an OSR of 250, the proposed ADC achieves a signal-to-noise-and-distortion-ratio (SNDR) of 102.8 dB, while dissipating 1.3 mW.

This paper describes the development of four different ultra-high frequency (UHF) radio frequency identification (RFID) tag antenna using polycarbonate material or transparent paper as the substrate and aluminum tape as the radiating element. The main advantage of the method is that the materials are easy to obtain where it can be found in any hardware stores or in any general online shop. Plus, the antennas are designed in such a way that a meander line is traced along the shape of a bowtie antenna so that the antenna would operate at UHF band. The results of all four of the tag antenna designs are discussed and compared using graph obtained from Computer Simulation Technology (CST) simulation results and measurement results obtained from a portable Vector Network Analyzer (VNA) for the reflection coefficient, S 11 , and measurement results taken from VNA in chamber room for the radiation pattern. Finally, the results show that the measured results are in agreement with the simulated result and that the UHF RFID tag antennas are able to operate at UHF RFID band.