Low Power Adaptive Circuits: An Adaptive Log Domain Filter and A Low Power Temperature Insensitive Oscillator Applied in Smart Dust Radio

This dissertation focuses on exploring two low power adaptive circuits. One is an adaptive filter at audio frequency for system identification. The other is a temperature insensitive oscillator for low power radio frequency communication. The adaptive filter is presented with integrated learning rules for model reference estimation. The system is a first order low pass filter with two parameters: gain and cut-off frequency. It is implemented using multiple input floating gate transistors to realize online learning of system parameters. Adaptive dynamical system theory is used to derive robust control laws in a system identification task. Simulation results show that convergence is slower using simplified control laws but still occurs within milliseconds. Experimental results confirm that the estimated gain and cut-off frequency track the corresponding parameters of the reference filter. During operation, deterministic errors are introduced by mismatch within the analog circuit implementation. An analysis is presented which attributes the errors to current mirror mismatch. The harmonic distortion of the filter operating in different inversion is analyzed using EKV model numerically. The temperature insensitive oscillator is designed for a low power wireless network. The system is based on a current starved ring oscillator implemented using CMOS transistors instead of LC tank for less chip area and power consumption. The frequency variance with temperature is compensated by the temperature adaptive circuits. Experimental results show that the frequency stability from 5°C to 65°C has been improved 10 times with automatic compensation and at least 1 order less power is consumed than published competitors. This oscillator is applied in a 2.2GHz OOK transmitter and a 2.2GHz phase locked loop based FM receiver. With the increasing needs of compact antenna, possible high data rate and wide unused frequency range of short distance communication, a higher frequency phase locked loop used for BFSK receiver is explored using an LC oscillator for its capability at 20GHz. The success of frequency demodulation is demonstrated in the simulation results that the PLL can lock in 0.5μs with 35MHz lock-in range and 2MHz detection resolution. The model of a phase locked loop used for BFSK receiver is analyzed using Matlab

Wideband Low Noise Oscillator suitable for Injection Locking

There is a growing need to design compact and low power transceiver circuits. The increasingly crowded frequency spectrum leads to increased challenges associated with transceiver design. In particular, it becomes imperative that the oscillator circuits have a low phase noise. RC oscillators have the ability to produce wideband oscillations with reduced area and low power consumption. However, a serious drawback is its high phase noise, which leads to poor circuit performance. To improve the performance of an RC oscillator, it is common for it to be integrated into a frequency synthesizer. The most common approach of a synthesizer is the Phase- Locked Loop (PLL). This approach leads to an increase in the area and complexity of the circuit. Another approach to a synthesizer is an Injection-Locked Oscillator (ILO), which achieves similar performances to a PLL without the disadvantages referred to above. In this thesis, an ILO based on an RC oscillator, using a Spin Torque Oscillator (STO) as a reference generator, is presented. The circuit is implemented in two different Complementary Metal-Oxide-Semiconductor (CMOS) technologies: 130 nm CMOS and 180 nm CMOS. The STO used as reference has characteristics similar to a nanometric device developed at the International Iberian Nanotechnology Laboratory (INL). In addition, the ILO operates in a wide frequency band ranging from 100 MHz to 3 GHz, has a power consumption ranging from 2.94 mW to 6.81 mW for 130 nm CMOS technology, whereas in 180nm CMOS technology it consumes between 4.86 mW and 13.96 mW. Thus, the work developed in the course of this thesis serves as proof of concept for the manufacture of a fully integrated hybrid ILO using the STO technology in conjunction with CMOS circuits

A Low-Power BFSK/OOK Transmitter for Wireless Sensors

In recent years, significant improvements in semiconductor technology have allowed consistent development of wireless chipsets in terms of functionality and form factor. This has opened up a broad range of applications for implantable wireless sensors and telemetry devices in multiple categories, such as military, industrial, and medical uses. The nature of these applications often requires the wireless sensors to be low-weight and energy-efficient to achieve long battery life. Among the various functions of these sensors, the communication block, used to transmit the gathered data, is typically the most power-hungry block. In typical wireless sensor networks, transmission range is below 10 meters and required radiated power is below 1 milliwatt. In such cases, power consumption of the frequency-synthesis circuits prior to the power amplifier of the transmitter becomes significant. Reducing this power consumption is currently the focus of various research endeavors. A popular method of achieving this goal is using a direct-modulation transmitter where the generated carrier is directly modulated with baseband data using simple modulation schemes. Among the different variations of direct-modulation transmitters, transmitters using unlocked digitally-controlled oscillators and transmitters with injection or resonator-locked oscillators are widely investigated because of their simple structure. These transmitters can achieve low-power and stable operation either with the help of recalibration or by sacrificing tuning capability. In contrast, phase-locked-loop-based (PLL) transmitters are less researched. The PLL uses a feedback loop to lock the carrier to a reference frequency with a programmable ratio and thus achieves good frequency stability and convenient tunability. This work focuses on PLL-based transmitters. The initial goal of this work is to reduce the power consumption of the oscillator and frequency divider, the two most power-consuming blocks in a PLL. Novel topologies for these two blocks are proposed which achieve ultra-low-power operation. Along with measured performance, mathematical analysis to derive rule-of-thumb design approaches are presented. Finally, the full transmitter is implemented using these blocks in a 130 nanometer CMOS process and is successfully tested for low-power operation

Integrated RF oscillators and LO signal generation circuits

This thesis deals with fully integrated LC oscillators and local oscillator (LO) signal generation circuits. In communication systems a good-quality LO signal for up- and down-conversion in transmitters is needed. The LO signal needs to span the required frequency range and have good frequency stability and low phase noise. Furthermore, most modern systems require accurate quadrature (IQ) LO signals. This thesis tackles these challenges by presenting a detailed study of LC oscillators, monolithic elements for good-quality LC resonators, and circuits for IQ-signal generation and for frequency conversion, as well as many experimental circuits. Monolithic coils and variable capacitors are essential, and this thesis deals with good structures of these devices and their proper modeling. As experimental test devices, over forty monolithic inductors and thirty varactors have been implemented, measured and modeled. Actively synthesized reactive elements were studied as replacements for these passive devices. At first glance these circuits show promising characteristics, but closer noise and nonlinearity analysis reveals that these circuits suffer from high noise levels and a small dynamic range. Nine circuit implementations with various actively synthesized variable capacitors were done. Quadrature signal generation can be performed with three different methods, and these are analyzed in the thesis. Frequency conversion circuits are used for alleviating coupling problems or to expand the number of frequency bands covered. The thesis includes an analysis of single-sideband mixing, frequency dividers, and frequency multipliers, which are used to perform the four basic arithmetical operations for the frequency tone. Two design cases are presented. The first one is a single-sideband mixing method for the generation of WiMedia UWB LO-signals, and the second one is a frequency conversion unit for a digital period synthesizer. The last part of the thesis presents five research projects. In the first one a temperature-compensated GaAs MESFET VCO was developed. The second one deals with circuit and device development for an experimental-level BiCMOS process. A cable-modem RF tuner IC using a SiGe process was developed in the third project, and a CMOS flip-chip VCO module in the fourth one. Finally, two frequency synthesizers for UWB radios are presented

Design and implementation of a frequency synthesizer for an IEEE 802.15.4/Zigbee transceiver

The frequency synthesizer, which performs the main role of carrier generation for the down-conversion/up-conversion operations, is a key building block in radio transceiver front-ends. The design of a synthesizer for a 2.4 GHz IEEE 802.15.4/Zigbee transceiver forms the core of this work. This thesis provides a step-by-step procedure for the design of a frequency synthesizer in a transceiver environment, from the mapping of standard-specifications to its integrated circuit implementation in a CMOS technology. The results show that careful system level planning leads to high-performance realizations of the synthesizer. A strategy of using different supply voltages to enhance the performance of each building block is discussed. A section is presented on layout and board level issues, especially for radio-frequency systems, and their effect on synthesizer performance. The synthesizer consumes 15.5 mW and meets the specifications of the 2.4 GHz IEEE 802.15.4/Zigbee standard. It is capable of 5 GHz operation with a VCO sensitivity of 135 MHz/V and a tuning range of 700 MHz. It can be seen that the adopted methodology can be used for the design of high-performance frequency synthesizers for any narrow-band wireless standard

Advanced deep space communication systems study Final report

Deep space communication system requirements for period 1970 to 198

Compensation for distribution of timing and reference signals over optical fibre networks for telescope arrays

Significant advancements and developments have been made in optical frequency standards, in recent years. In order to verify the accuracy and preciseness of the disseminated RF signal, it is essential to compare its stability with the standards provided in literature as well as by metrology institutes. However, conventional frequency comparison techniques via satellites have extremely inferior stability qualities. As a result, the need for an alternative ultra-high precision RF transfer method presented itself. Highly accurate and precise frequency dissemination across optical fiber has proved a leading contender and a possible solution. When compared to conventional data transfer media, optical fiber has proven to be more superior and yields lower transmission errors and is immune to radio frequency interference. A further quality of optical fibre is that its transmission distance can be extended to greater degree than the traditional coaxial cable due to its low loss property. This thesis deals with the compensation of phase noise in single mode optical fibre. Phase noise degrades the performance and stability of the RF signal as well as the optical carrier frequency across long-haul optical networks. This work begins by experimentally demonstrating a unique and novel way for measuring the round-trip optical fibre latency times. The technique is based on all optical wavelength conversion using a stable PPS injection signal. The result highlighted the importance for active phase error compensation along a fibre link. Various computer simulations were used to study the influence of temperature fluctuation on the optical fibre. The first ever error signals generated at NMU was experimentally demonstrated. Results illustrated that, by minimizing the error voltage the phase difference between the transmitted and reference signals were reduced to zero. Performance analysis testing of the VCSEL phase correction actuator showed that majority of the dither iterations that induced the phase compensation took approximately 0.15 s. Residual frequency instabilities of 3.39791 x 10-12 at 1 s and 8.14848 x 10-12 at 103 s was measured when the 26 km G.655 fibre link was running freely. Experimental results further showed that the relative frequency stabilities measured at 1 s and 103 s were 4.43902 x 10-12 and 1.62055 x 10-13 during active compensation, respectively. The novel work presented in this thesis is exciting since the VCSEL is used as the optical source as well as the phase correction actuator. The benefits of such a device is that is reduces system costs and complexities

Generation of terahertz-modulated optical signals using AlGaAs/GaAs laser diodes

The Thesis reports on the research activities carried out under the Semiconductor-Laser Terahertz-Frequency Converters Project at the Department of Electronics and Electrical Engineering, University of Glasgow. The Thesis presents the work leading to the demonstration of reproducible harmonic modelocked operation from a novel design of monolithic semiconductor laser, comprising a compound cavity formed by a 1-D photonic-bandgap (PBG) mirror. Modelocking was achieved at a harmonic of the fundamental round-trip frequency with pulse repetition rates from 131 GHz up to a record-high frequency of 2.1 THz. The devices were fabricated from GaAs/AlGaAs material emitting at a wavelength of 860 nm and incorporated two gain sections with an etched PBG reflector between them, and a saturable absorber section. Autocorrelation studies are reported, which allow the device behaviour for different modelocking frequencies, compound cavity ratios, and type and number of intra-cavity reflectors to be analyzed. The highly reflective PBG microstructures are shown to be essential for subharmonic-free modelocking operation of the high-frequency devices. It was also demonstrated that the multi-slot PBG reflector can be replaced with two separate slots with smaller reflectivity. Some work was also done on the realisation of a dual-wavelength source using a broad-area laser diode in an external grating-loaded cavity. However, the source failed to deliver the spectrally-narrow lines required for optical heterodyning applications. Photomixer devices incorporating a terahertz antenna for optical-to microwave down-conversion were fabricated, however, no down-conversion experiments were attempted. Finally, novel device designs are proposed that exploit the remarkable spectral and modelocking properties of compound-cavity lasers. The ultrafast laser diodes demonstrated in this Project can be developed for applications in terahertz imaging, medicine, ultrafast optical links and atmospheric sensing

Ultra Low Power FM-UWB Transceiver for High-Density Wireless Sensor Networks

The WiseSkin project aims to provide a non-invasive solution for restoration of a natural sense of touch to persons using prosthetic limbs. By embedding sensor nodes into the silicone coating of the prosthesis, which acts as a sensory skin, WiseSkin targets to provide improved gripping, manipulation and mobility for amputees. Flexibility, freedom of movement and comfort demand unobtrusive, highly miniaturized, low-power sensing capabilities built into the artificial skin, which is then integrated with a sensory feedback system. Wireless communication between the sensor nodes provides more flexibility, better scalability and robustness compared to wired solution, and is therefore a preferred approach for WiseSkin. Design of an RF transceiver tailored for the specific needs of WiseSkin is the topic of this work. The properties of FM ultra-wide band (FM-UWB) modulation make it a good candidate for High-Density Wireless Sensor Networks (HD-WSN). The proposed FM-UWB receivers take advantage of short range to reduce power consumption, and exploit robustness of this wideband modulation scheme. The LNA, identified as the biggest consumer, is removed and signal is directly converted to dc, where amplification and demodulation are performed. Owing to 500 MHz bandwidth, frequency offset and phase noise can be tolerated, and a low-power, free-running ring oscillator can be used to generate the LO signal. The receiver is referred to as an approximate zero-IF receiver. Two receiver architectures are studied. The first one performs quadrature downconversion, and owing to the demodulator linearity, provides the multi-user capability. In the second receiver, quadrature demodulation is replaced by the single-ended one. Due to the nature of the demodulator, sensitivity degrades, and multiple FM-UWB signals cannot be resolved, but the consumption is almost halved compared to the first receiver. The proposed approach is verified through two integrations, both in a standard 65 nm bulk CMOS process. In the first run, a standalone quadrature receiver was integrated. Power consumption of 423 uW was measured, while achieving -70 dBm sensitivity. Good narrow-band interference rejection and multiuser capability with up to 4 FM-UWB channels could be achieved. In the second run, a full transceiver is integrated, with both quadrature and single-ended receivers and a transmitter, all sharing a single IO pad, without the need for any external passive components or switches. The quadrature receiver, with on-chip baseband processing and multi-user support, in this case consumes 550 uW, with a sesensitivity of -68 dBm. The low power receiver consumes 267 uW, and provides -57 dBm sensitivity, at a single FM-UWB channel. The implemented trantransmitter transmits a 100 kb/s FM-UWB signal at -11.4 dBm, while drawing 583 uW from the 1 V supply. The on-chip clock recovery allows reference frequency offset up to 8000 ppm. Since state of the art on-chip RC oscillators can provide below 2100 ppm across the temperature range of interest, the implemented transceiver demonstrates the feasibility of a fully integrated FM-UWB radio with no need for a quartz reference or any external components. In addition, the transceiver can tolerate up to 3 dBm narrow-band interferer at 2.4 GHz. Such a strong signal can be used to remotely power the sensor nodes inside the artificial skin and enable a truly wirelessWiseSkin solution