Integrated radio frequency synthetizers for wireless applications

This thesis consists of six publications and an overview of the research topic, which is also a summary of the work. The research described in this thesis concentrates on the design of phase-locked loop radio frequency synthesizers for wireless applications. In particular, the focus is on the implementation of the prescaler, the phase detector, and the chargepump. This work reviews the requirements set for the frequency synthesizer by the wireless standards, and how these requirements are derived from the system specifications. These requirements apply to both integer-N and fractional-N synthesizers. The work also introduces the special considerations related to the design of fractional-N phase-locked loops. Finally, implementation alternatives for the different building blocks of the synthesizer are reviewed. The presented work introduces new topologies for the phase detector and the chargepump, and improved topologies for high speed CMOS prescalers. The experimental results show that the presented topologies can be successfully used in both integer-N and fractional-N synthesizers with state-of-the-art performance. The last part of this work discusses the additional considerations that surface when the synthesizer is integrated into a larger system chip. It is shown experimentally that the synthesizer can be successfully integrated into a complex transceiver IC without sacrificing the performance of the synthesizer or the transceiver.reviewe

Low Noise, Narrow Optical Linewidth Semiconductor-based Optical Comb Source And Low Noise Rf Signal Generation

Recently optical frequency combs and low noise RF tones are drawing increased attention due to applications in spectroscopy, metrology, arbitrary waveform generation, optical signal processing etc. This thesis focuses on the generation of low noise RF tones and stabilized optical frequency combs. The optical frequency combs are generated by a semiconductor based external cavity mode-locked laser with a high finesse intracavity etalon. In order to get the lowest noise and broadest bandwidth from the mode-locked laser, it is critical to know the free spectral range (FSR) of the etalon precisely. First the etalon FSR is measured by using the modified Pound-Drever-Hall (PDH) based method and obtained a resolution of 1 part in 106 , which is 2 order of magnitude better than the standard PDH based method. After optimizing the cavity length, RF driving frequency and PDH cavity locking point, the mode-locked laser had an integrated timing jitter of 3 fs (1 Hz- 100 MHz) which is, to the best of our knowledge, the lowest jitter ever reported from a semiconductor based multigigahertz comb source. The modelocked laser produces ~ 100 comb lines with 10 GHz spacing, a linewidth of ~500 Hz and 75 dB optical signal-to-noise ratio. The same system can also be driven as a regeneratively modelocked laser with greatly improved noise performance. Another way of generating a low noise RF tone is using an opto-electronic oscillator which uses an optical cavity as a high Q element. Due to the harmonic nature of OEOs, a mode selection element is necessary. Standard OEOs use an RF filter having drawbacks such as broad pass band, high loss, and high thermal noise. In our work, a novel optoelectronic scheme which uses an optical filter (Fabry-Perot etalon) as the mode filter instead of an RF filter is demonstrated. This method has the advantage of having ultra-narrow filtering bandwidths ( ~ 10 iv kHz for a 10 GHz FSR and 106 finesse) and an extremely low noise RF signal. Experimental demonstration of the proposed method resulted in a 5-10 dB decrease of the OEO noise compared to the conventional OEO setup. Also, by modifying the etalon-based OEO, and using single side band modulation, an optically tunable optoelectronic oscillator is achieved with 10-20 dB lower noise than dual side band modulation. Noise properties of the OEO as a function of optical frequency detuning is also analyzed theoretically and the results are in agreement with experimental results. The thesis concludes with comments on future work and directions

Special arod system studies seventh quarterly report

Phase lock loop advanced circuits, and technical summary for Airborne Range and Orbit Determination /AROD/ syste

Special AROD System Studies, Volume I Fifth Quarterly Report, Period Ending Dec. 31, 1964

Wideband modulation techniques and phase-locked loop studies for airborne range and orbit determination syste

Receiver Front-Ends in CMOS with Ultra-Low Power Consumption

Historically, research on radio communication has focused on improving range and data rate. In the last decade, however, there has been an increasing demand for low power and low cost radios that can provide connectivity with small devices around us. They should be able to offer basic connectivity with a power consumption low enough to function extended periods of time on a single battery charge, or even energy scavenged from the surroundings. This work is focused on the design of ultra-low power receiver front-ends intended for a receiver operating in the 2.4GHz ISM band, having an active power consumption of 1mW and chip area of 1mm². Low power consumption and small size make it hard to achieve good sensitivity and tolerance to interference. This thesis starts with an introduction to the overall receiver specifications, low power radio and radio standards, front-end and LO generation architectures and building blocks, followed by the four included papers. Paper I demonstrates an inductorless front-end operating at 915MHz, including a frequency divider for quadrature LO generation. An LO generator operating at 2.4GHz is shown in Paper II, enabling a front-end operating above 2GHz. Papers III and IV contain circuits with combined front-end and LO generator operating at or above the full 2.45GHz target frequency. They use VCO and frequency divider topologies that offer efficient operation and low quadrature error. An efficient passive-mixer design with improved suppression of interference, enables an LNA-less design in Paper IV capable of operating without a SAW-filter

Tunable coupling to a mechanical oscillator circuit using a coherent feedback network

We demonstrate a fully cryogenic microwave feedback network composed of modular superconducting devices connected by transmission lines and designed to control a mechanical oscillator coupled to one of the devices. The network features an electromechanical device and a tunable controller that coherently receives, processes and feeds back continuous microwave signals that modify the dynamics and readout of the mechanical state. While previous electromechanical systems represent some compromise between efficient control and efficient readout of the mechanical state, as set by the electromagnetic decay rate, the tunable controller produces a closed-loop network that can be dynamically and continuously tuned between both extremes much faster than the mechanical response time. We demonstrate that the microwave decay rate may be modulated by at least a factor of 10 at a rate greater than $10^4$ times the mechanical response rate. The system is easy to build and suggests that some useful functions may arise most naturally at the network-level of modular, quantum electromagnetic devices.Comment: 11 pages, 6 figures, final published versio

Multi-link laser interferometer architecture for a next generation GRACE

When GRACE Follow-On (GRACE-FO) launches, it will be the first time a laser interferometer has been used to measure displacement between spacecraft. In the future, interspacecraft laser interferometry will be used in LISA, a space-based gravitational wave detector, that requires the change in separation between three spacecraft to be measured with a resolution of 1 pm/rtHz. The sensitivity of an interspacecraft interferometer is potentially limited by spacecraft degrees-of-freedom, such as rotation, coupling into the interspacecraft displacement measurement. GRACE-FO and LISA therefore have strict requirements placed on the positioning and alignment of the interferometers during spacecraft integration. Decades of work has gone into adapting traditionally lab-based techniques for these space applications. As an example, GRACE-FO stops rotation of the two spacecraft from coupling into displacement using the triple mirror assembly. The triple mirror assembly is a precision optic, comprised of three mirrors, that function as a retroreflector. Provided the triple mirror assembly vertex coincides with the spacecraft centre of mass, any spacecraft rotation will asymmetrically lengthen and shorten the optical pathlengths of the incoming and outgoing beams, ensuring that the round trip pathlength between the spacecraft is unaffected. To achieve the required displacement sensitivity, the triple mirror assembly vertex must be positioned within 0.5 mm of the spacecraft centre of mass, making spacecraft integration challenging. In this thesis a new, all-fibre interferometer architecture is presented that aims to simplify the positioning and alignment of space-based interferometers. Using multiple interspacecraft link measurements and high-speed signal processing the interspacecraft displacement is synthesised in post-processing. The multi-link interferometry concept is similar to the triple mirror assembly's symmetric suppression of rotation, however, since the rotation-to-pathlength cancellation is performed in post-processing, the weighting of each interspacecraft link measurement can be optimised to completely cancel any rotation coupled error. Consequently, any uncertainty in the positioning of the multi-link interferometer during spacecraft integration can be corrected for in post-processing. The strict hardware integration requirements of current interferometers can therefore be relaxed, enabling a new class of simpler, cheaper missions. The multi-link concept is evaluated as a potential interferometer architecture for a next generation GRACE mission. The multi-link GRACE concept uses several fibre coupled optical heads on each spacecraft to form multiple interspacecraft links between spacecraft. To cancel rotation coupled error from rotation of both spacecraft, 9 interspacecraft links are formed between 3 optical heads positioned on each spacecraft. Displacement is measured in both directions along each link using digitally implemented phasemeters. The 18 interspacecraft displacement measurements are then combined using artificial delays and different weights to cancel laser frequency equivalent displacement noise, fibre pathlength fluctuations and rotation coupled displacement error. The interferometer uses digitally enhanced heterodyne interferometry to multiplex the multiple link beatnotes; Time delay interferometry is used to suppress the laser frequency displacement noise and fibre fluctuations; and, to simplify the acquisition of the multiple interspacecraft links, the beam divergence out of each optical head is made sufficiently large so that links can be acquired without requiring a dedicated link acquisition strategy. Although this design simplifies the spacecraft integration and alignment it comes with some challenges: without an active link acquisition, the received power on the distant spacecraft could be considerably lower than in GRACE-FO; time delay interferometry has not been tested on a GRACE-like interferometer; and the cancellation of rotation-to-pathlength coupled error using a weighted average of multiple link measurements has not been demonstrated. Three experiments are presented in this thesis, addressing these challenges. In both GRACE-FO and LISA, phasemeters are used to track the phase of the lasers transmitted along each interspacecraft link. Tracking the phase of optical signals with low signal-to-noise ratios (SNR) is difficult because the higher, relative noise can lead to nonlinear behaviour in the phasemeter. In the first experiment presented in this thesis, the dominant noise sources -- laser frequency noise and shot noise -- that limit the phasemeter's ability to track low SNR signals are analysed. By optimising the phasemeter bandwidth to minimise the error from these two noise sources, the probability of nonlinear phasemeter behaviour is also minimised. A benchtop demonstration was performed to verify the analysis, with the bandwidth optimisation used to track a 30 fW free-running signal - the lowest power signal that has been tracked to date. The analysis indicates that subfemtowatt signals could be tracked if the laser frequency is pre-stabilised. The second experiment describes the development of a time delay interferometry combination for a GRACE-like interferometer that recovers the displacement sensitivity of the phase locked GRACE-FO interferometer. The combination could be used to test time delay interferometry on GRACE-FO as part of the LISA Experience On Grace OpticalPayload (LEGOP) project. It also demonstrates time delay interferometry could be used on a GRACE-like interferometer for laser frequency displacement noise suppression. The proposed test uses a tone assisted time delay interferometric ranging (TDIR) algorithm to determine the delays required to suppress the displacement noise due to one laser in the displacement measurement between the GRACE spacecraft. Under simulated GRACEFO conditions, the tone assisted TDIR algorithm was used to suppress the laser frequency equivalent displacement noise by 8 orders of magnitude. This was below the residual laser frequency displacement noise requirement on GRACE-FO of 20 nm/rtHz. An experimental test of the algorithm demonstrated the capabilities of the proposed algorithm in the presence of large path length fluctuations, a macroscopic optical delay and different electronic delays. The third experiment tested the multi-link GRACE architecture. In the benchtop experiment a local spacecraft with 3 optical heads was modeled. Pitch and yaw of the local spacecraft were emulated using the tip and tilt actuators on a piezo-electric steering mirror. The displacement was measured along 3 links formed between the local optical heads and a single distant spacecraft optical head. Using a weighted average of the 3 link measurements, rotation-to-pathlength coupled error from the simulated pitch and yaw of the local spacecraft were suppressed by up to 18 dB. In addition to spacecraft rotation, tones were injected to model laser frequency noise, fibre uctuations and an `interspacecraft'displacement signal. The laser noise, fibre noise and rotation-to-pathlength noise were all suppressed down to the 1 nm/rtHz measurement noise floor without affecting the measurement of the `interspacecraft' displacement signal. The results of the three experiments, along with a prediction of the displacement sensitivity in a multi-link GRACE, verify the feasibility of the multi-link architecture. More testing and development is needed however before a multi-link GRACE can be realised, with a number of these tests outlined in the discussion