PLL-based high-speed demodulation of FM signals for real-time AFM applications

In this paper we present a new architecture for PLL-based high-speed demodulation of frequency-modulated AFM signals. In our approach, we use single-sideband frequency up-conversion to translate the AFM signal from the position sensitive detector to a fixed intermediate frequency of 10MHz. In this way, we fully benefit from the excellent noise performance of PLL-based FM demodulators still avoiding the intrinsic bandwidth limitation of such systems. Furthermore, the system becomes independent of the cantilever's resonance frequency. To investigate if the additional noise introduced by the single-sideband upconverter degrades the system noise figure we present a model of the AM-to-FM noise conversion in the PLL phase detector. Using this model, we can predict an upper corner frequency for the demodulation bandwidth above which the converted noise from the single-sideband upconverter becomes the dominant noise source and therefore begins to deteriorate the overall system performance. The approach is validated by measured data obtained with a PCB-based prototype implementing the proposed demodulator architecture. © 2013 IEEE

Single-Cycle-PLL Detection for Real-Time FM-AFM Applications

In this paper we present a novel architecture for phase-locked loop (PLL) based high-speed demodulation of fre- quency-modulated (FM) atomic force microscopy (AFM) signals. In our approach, we use single-sideband (SSB) frequency upcon- version to translate the AFM signal from the position sensitive detector to a fixed intermediate frequency (IF) of 10 MHz. In this way, we fully benefit from the excellent noise performance of PLL-based FM demodulators still avoiding the intrinsic band- width limitation of such systems. In addition, the upconversion to a fixed IF renders the PLL demodulator independent of the cantilever’s resonance frequency, allowing the system to work with a large range of cantilever frequencies. To investigate if the additional noise introduced by the SSB upconverter degrades the system noise figure we present a model of the AM-to-FM noise conversion in PLLs incorporating a phase-frequency detector. Using this model, we can predict an upper corner frequency for the demodulation bandwidth above which the converted noise from the single-sideband upconverter becomes the dominant noise source and therefore begins to deteriorate the overall system performance. The approach is validated by both electrical and AFM measurements obtained with a PCB-based prototype imple- menting the proposed demodulator architecture

Engineering evaluations and studies. Volume 3: Exhibit C

High rate multiplexes asymmetry and jitter, data-dependent amplitude variations, and transition density are discussed

DISEÑO DE UN DEMODULADOR DE FM MEDIANTE PLL PARA LA INTERROGACIÓN DE SENSORES INTERFEROMÉTRICOS DE FIBRA ÓPTICA

ResumenEn este trabajo se diseñó y se construyó un sistema de interrogación de sensores interferométricos. El sistema está constituido por una etapa que emula la señal interferométrica típica de un sensor de este tipo: Primeramente, una etapa de acondicionamiento que convierte esta señal en una señal de FM convencional y finalmente una etapa de demodulación de frecuencia; mediante el uso de la técnica de amarre de fase PLL, (del inglés: Phase Lock Loop). El proceso de demodulación, denominado en la literatura como “heterodino sintético”, utiliza un par de osciladores locales sintonizados a la frecuencia de la señal portadora y al doble de ésta. Así mismo, se requirieron una serie de filtros pasabanda tipo Butterworth de segundo orden para acotar el espectro de las señales de interés centrados en la frecuencia de la armónica necesaria para realizar el proceso de mezclado. Finalmente, la señal acondicionada se usó como entrada a un demodulador de FM mediante un PLL. Se consiguió recuperar señales del orden de miliradianes en el rango de 90 a 260 Hz. Se observó que este rango dependió del ancho de banda de los filtros pasabanda utilizados en el circuito. Se optó por esta técnica de demodulación basada en un PLL, pues logra la sintonización de una amplia gama de frecuencias, al ser también sintonizable el PLL a través de su VCO.Palabras Claves: Demoduladores de FM, fase óptica, sensores interferométricos, PLL. DESIGN OF AN FM DEMODULATOR THROUGH PLL FOR THE INTERROGATION OF OPTICAL FIBER INTERFEROMETRIC SENSORSAbstractIn this work, an interrogation system of interferometric sensors was designed and constructed. The system consists of a stage emulating the interferometric signal typical of such sensor: First a conditioning stage that converts the above signal into a conventional FM signal and finally a frequency demodulation stage, based in the Phase Lock Loop technique o demodulate FM signals (PLL). The demodulation process used here, referred in the literature as "synthetic heterodyne", uses a pair of local oscillators, one tuned to the frequency of the carrier signal and the other one tuned at twice of the carrier frequency. It also requires a series of second-order Butterworth bandpass filters to limit the signals of interest and maintain a constant amplitude in the passband. As well as a trimmer to minimize the amplitude changes, in the final part of the conditioning stage. Finally, the conditioned signal was used as input to an FM demodulator via a PLL and signals of the order of miliradianes were achieved; with frequencies of modulating signals in the range of 90 to 260 Hz. It was observed that this range depended on the bandwidth of the bandpass filters used in the circuit.Keywords: FM demodulators, Interferometric sensors, optical phase, PLL

Visualisation of Local Charge Densities with Kelvin Probe Force Microscopy

For the past decades, Kelvin probe force microscopy (KPFM) developed from a sidebranch of atomic force microscopy to a widely used standard technique. It allows to measure electrostatic potentials on any type of sample material with an unprecedented spatial resolution. While the technical aspects of the method are well understood, the interpretation of measured data remains object of intense research. This thesis intends to prove an advanced view on how sample systems which are typical for ultrahigh resolution imaging, such as organic molecular submonolayers on metals, can be quantitavily analysed with the differential charge density model. In the first part a brief introduction into the Kelvin probe experiment and atomic force microscopy is given. A short review of the theoretical background of the technique is presented. Following, the differential charge density model is introduced, which is used to further explain the origin of contrast in Kelvin probe force microscopy. Physical effects, which cause the occurence of local differential charge densities, are reviewed for several sample systems that are of interest in high resolution atomic force microscopy. Experimental evidence for these effects is presented in the second part. Atomic force microscopy was used for in situ studies of a variety of sample systems ranging from pristine metal surfaces over monolayer organic adsorbates on metals to ferroelectric substrates both, with and without organic thin film coverage. As the result from these studies, it is shown that the differential charge density model accurately describes the experimentally observed potential contrasts. This implies an inherent disparity of the measurement results between the different Kelvin probe force microscopy techniques; a point which had been overseen so far in the discussion of experimental data. Especially for the case of laterally strong confined differential charge densities, the results show the opportunity as well as the necessity to explain experimental data with a combination of ab initio calculations of the differential charge density and an electrostatic model of the tip-sample interaction

Demodulator techniques in satellite communication systems for direct broadcast systems

This thesis is concerned with the FM demodulator techniques used in terrestrial TV receiver designs for Direct Broadcast Systems (DBS) from satellites. The various MAC/Packet schemes intended for DBS applications are described and the international standards that apply to them considered, with particular emphasis on the D2-MAC system. Noise in FM systems is discussed and a suitable threshold noise model is chosen for use in DBS TV demodulator systems. The characteristics of the various types of noise effects are considered in terms of their effect upon the TV picture. The threshold performance of a conventional FM demodulator for differing types of modulation is reviewed and it is shown how the threshold characteristic depends upon the nature of the modulation. The literature review carried out represents a significant component of the thesis and combines material from patent literature with more conventional source materials from professional journals, conferences, textbooks, etc. Some ten existing demodulator concepts that exhibit threshold extension characteristics are examined, and where relevant their potential performance in D2-MAC format systems is assessed. The demodulator characteristics that limit their performance in TV systems are identified. It is concluded that designing a threshold extension demodulator, with reliable operation, for all picture contents and for a wide range of input carrier-to-noise ratios, is a formidable task using existing design techniques. On the basis of this examination an adaptive threshold extension demodulator concept is proposed, that utilises information contained within the signal structure to achieve an improved performance over a wide range of input carrier-to-noise ratios and picture content. It is shown how the relevant signal structures may be derived from conventional (PAL, SECAM and NTSC), MAC format and all-digital television systems. Illustrations are given that show how the adaptive demodulator concept can be applied to certain existing threshold extension demodulators, enhancing their performance for television picture reception. Future trends in all-digital DBS TV systems intended ultimately for DBS applications are briefly discussed together with their demodlilation requirements

Characterization of a home-built low temperature scanning probe microscopy system

The continuing advancement of technology is the driving force behind science and fundamental research. Scanning probe instruments still have a major impact in nanoscience and technology, because they provide a link between the macroscopic world and the atomic scale. The key to a reliable performance of experiments at the nanometer scale is the instrumentation, that allows probe positioning ranging from micrometers to Ångstroms with sub atomic precisions. A new type of scanning probe microscopy (SPM) system operating in ultra high vacuum (UHV) and at liquid Helium (LHe) temperature was developed. This offers the advantages that even reactive surfaces remain clean over time periods of several days, permitting long time experiments. Moreover, these experiments this low temperature scanning probe microscopy (LTSPM) system is the implementation of a focussing Fabry Perot interferometer (fFPi) that allows the following features: - Small amplitude operations and stiff cantilevers require sensors with high deflection sensitivity. With the fFPi in this low temperature SPM system, a deflection sensitivity of 4fm/ sqrt(Hz) at 1MHz can be obtained. - Wide detection bandwidth (DC-10MHz) enables the operation of higher flexural oscillation modes as well as the torsional modes of the cantilever. - A laser spot size of 3µm allows the use of ultra small cantilevers with the dimensions 1/10 of conventional cantilevers. - Photothermal excitation of cantilevers avoids undesirable mechanical vibrations near the cantilever resonance frequency. - Simultaneous flexural and torsional force detection provides quantitative studies of frictions and thus, atom manipulations by atomic force microscopy (AFM). - The combination of both types of microscopes (simultaneous AFM/STM) reveals more information than a scanning tunneling microscopy (STM) or AFM alone. A series of measurements on Si(111)7x7, herringbone superstructure of Au(111) and highly oriented pyrolytic graphite (HOPG) provides information regarding imaging performance of the system. Among these performance tests are atomically resolved scans at three different operating temperatures in STM mode. In non-contact atomic force microscopy (nc-AFM) mode, imaging was performed with the cantilever driven at the fundamental and 2nd oscillation mode. Additional measurements were performed with the fFPi in order to quantify the impact of the laser cooling effects (radiation pressure and photothermal effects) on the oscillating cantilever at three different operating temperatures. The aim of this work is the development, implementation and characterization of a new low temperature scanning probe microscope with an ultra sensitive and high bandwidth fFPi deflection sensor, suitable for nc-AFM operations with small, simultaneous flexural and torsional cantilever oscillation modes. Furthermore, expected upgrades will allow simultaneous nc-AFM/STM operations. Keywords: low temperature home-built simultaneous STM/ nc-AFM, tip-sample gap stability, PLL and self-excitation, highly oriented pyrolytic graphite (HOPG), reconstructed Si(111)7x7, herringbone superstructure, focussing Fabry-Perot interferometer, cantilever cooling, radiation pressure and photothermal effects. Der kontinuierliche, technologische Fortschritt ist die treibende Kraft hinter Wissenschaft und Grundlagenforschung. Rasterkraft und -tunnel Instrumente haben immer noch einen bedeutenden Einfluss auf die Nanotechnologie und -wissenschaft, weil sie eine Verbindung zwischen der makroskopischen Welt und den atomaren Massstäben darstellen. Der Schlüssel für eine zuverlässige Ausführung von Experimenten mit Nanometer Massstäben ist die Instrumentierung, die eine Spitzenpositionierung von Mikrometer bis Ångstroms mit subatomarer Präzision erlaubt. Ein neuartiges Rasterspitzen Mikroskop (SPM) System wurde entwickelt, das im Ultra Hoch Vakuum (UHV) und bei flüssig Helium Temperaturen arbeitet. Dies bietet Vorteile weil sogar reaktive Oberflächen über eine Dauer von einigen Tagen sauber bleiben, was eine längere Experimentierphase zulässt. Zusätzlich zeigen diese Experimente bei tiefen Temperaturen weitere Vorteile wie kleine Driftwerte und tiefe Piezo Kriechraten. Der Ansatz bei diesem Tieftemperatur Rasterspitzen Mikroskop System ist die Implementierung eines fokussierenden Fabry Perot Interferometers das die folgenden Eigenschaften vorweist: - Der Betrieb bei kleinen Amplituden und mit steifen Cantilever setzt Sensoren mit einer hohen Ablenkempfindlichkeit voraus. Mit diesem fokussierenden Fabry Perot Interferometer (fFPi) kann eine Ablenkempfindlichkeit von 4fm/ sqrt(Hz) bei 1MHz erreicht werden. - Detektion mit einer grossen Bandbreite (DC-10MHz) erlauben einen Betrieb von Cantilever mit flexuralen und torsionalen Oszillation Modi. - Ein Laser mit einem Brennpunkt von 3µm lässt einen Betrieb mit einem ultra kleinen Cantilever zu, der 1/10 so gross ist wie ein konventioneller Cantilever. - Photothermische Anregung eines Cantilevers vermeidet unerwünschte mechanische Vibrationen rund um die Resonanzfrequenz. - Gleichzeitige flexural und torsional Kraftdetektion erlauben quantitative Untersuchungen von Reibungen und daher atomare Manipulationen mit Rasterkraft Mikroskopie (AFM). - Die Kombination und simultanen Betrieb von beiden Rasterspitzen Mikroskopen (AFM/STM) zeigen mehr Information als ein Raster Tunnel Mikroskop (STM) alleine. Eine Serie von Messungen mit Si(111)7x7, Herringbone Superstrukturen auf Au(111) und Highly Oriented Pyrolytic Graphite (HOPG) geben Information bezüglich der Leistungen des Systems preis. Einige dieser Leistungstests sind atomar aufgelöste Abbildungen bei drei unterschiedlichen Betriebstemperaturen im STM Betriebsart. Im nicht-Kontakt AFM (nc-AFM) Betriebsart, Abbildungen sind ausgeführt worden auf der Grundschwingung und der zweiten Oberschwingung. Zusätzliche Messungen wurden mit dem fFPi ausgeführt um den Einfluss der Laserkühlung auf den oszillierenden Cantilever bei drei unterschiedlichen Betriebstemperaturen zu quantifizieren. Das Ziel dieser Arbeit ist die Entwicklung, Implementation und Charakterisierung eines neuen Tieftemperatur Rasterspitzen Mikroskops mit einem ultra-empfindlichen und Breitband fokussierenden Fabry Perot Interferometer Ablenk Sensor, geeignet für den nicht-Kontakt AFM Betrieb mit kleinen, simultanen flexural und torsional Cantilever Schwingungsmodi. Naheliegende Erweiterungen des Systems gewährleisten einen simultan nc-AFM/STM Betrieb. Schlüsselwörter: Tieftemperatur simultan nc-AFM/STM aus Eigenbau, Spitzen-Probe Spalt Stabilität, PLL und Eigenanregungsbetrieb, Highly Oriented Pyrolytic Graphite (HOPG), reconstrukturiertes Si(111)7x7, Herringbone Superstruktur, fokussierenden Fabry Perot Interferometer, Cantilever Kühlung, Strahlendruck und photothermische Effekte

Multi-Eigenmode Control for Improved Tracking Speed in Multifrequency Atomic Force Microscopy

Die Sensoren von Rasterkraftmikroskopen sind mechanische Schwinger, die zur zeitgleichen Aufnahmevon Topographie und Materialeigenschaften genutzt werden können. Besonders wichtig sinddie Bildrastergeschwindigkeit und Kraftsensitivität, die oft einen Kompromiss benötigen. In dieserArbeit wird ein neuartiger Multi-Eigenmode Kompensator basierend auf einem Zustandsschätzervorgestellt, der die dynamischen Eigenschaften jeder Cantilever-Resonanz unabhängig voneinandermodifizieren kann. Dargelegt wird die Modellierung, Kompensator-Design und Implementierungsstrategiein ein digitales System. Als Erstes wird der Kompensator zur Modifikation desQ Faktors einzelner Eigenmoden genutzt. Somit kann die Abbildungsrate um das 20-fache erhöhtwerden. Die Modifikation der natürlichen Frequenz erlaubt die Abbildung von Proben mitvollständig verschobenen Resonanzen. Moderne Mehrfachfrequenz-Abbildungsverfahren nutzenhöheren Eigenmoden, um bessere Abbildungsraten und Materialsensitivitäten zu erreichen. Beieiner Methode werden die angeregten höheren Harmonischen extrahiert, die beim Rastern einerOberfläche im Fourier-Spektrum entstehen. Eine andere Methode regt die erste und höhere Eigenmodengleichzeitig an. In Experimenten wird der Kompensator in Kombination mit beiden Abbildungsverfahrengenutzt, um speziell den Q Faktor der ersten beiden transversalen Eigenmoden gleichzeitigzu beeinflussen. Experimente zeigen, dass beste Abbildungsraten und Materialkontrastemit geringen Q Faktoren in der ersten und hohen Q Faktoren in der zweiten Eigenmode erreichtwerden. Eine Erweiterung des Kompensators erlaubt die Hochgeschwindigkeits-Demodulationvon Cantilever-Amplituden ohne Einsatz eines Lock-in Verstärkers, was anhand von Abbildungenmit der ersten Eigenmode gezeigt wird. Eine weitere Möglichkeit zur Verbesserung des Materialkontrastesbasiert auf der strukturellen Modifikation des Cantilevers. Mit Hilfe einer Ionenfeinstrahlanlagewird Material an bestimmten Bereichen des Cantilevers entfernt, so dass die erste undhöheren Eigenmoden aufeinander abgestimmt werden. Die Bestimmung von Form und Ort derMaterialentfernung wird entweder durch Simulationen im Voraus oder mit einem in situ Ansatzerreicht. Die extrahierten höheren harmonischen Signale des harmonischen Cantilevers zeigen eindeutlich verstärktes Signal von bis zu 10 % im Vergleich zur ersten Resonanz.Atomic Force Microscope probes are mechanical beams that can be used to simultaneously maptopography and material properties. In particular the imaging speed and force sensitivity aremajor concerns that often require a trade-off approach. In this work, a novel estimator basedmulti-eigenmode compensator is introduced to modify the dynamics of each resonance independently.Modeling, compensator design, implementation strategy in a digital system and validationin experiments will be presented. A single-eigenmode version of the compensator is used to modifythe Q factor of the first three eigenmodes separately. Using higher eigenmodes in combinationwith a modified Q factor leads to a 20-fold increase in image acquisition rates. The modificationof the natural frequency (F control) allows imaging at resonance frequencies that are not naturalto the cantilever. The emerging multifrequency Atomic Force Microscopy utilizes higher eigenmodesto improve imaging speed and force sensitivity concurrently. One method actuates the firsteigenmode for topography imaging and records the excited higher harmonics to map a sample’snanomechanical properties. To enhance the higher frequencies’ response two or more eigenmodesare actuated simultaneously, where the higher eigenmodes are used to quantify the nanomechanics.In experiments, the compensator is used to specifically modify the Q factors of the cantilever’sfirst two transversal eigenmodes concurrently in both imaging schemes. The experiments indicatemost enhanced material contrast and imaging rate with low Q factors in the first eigenmode andhigh Q factors in the higher eigenmode. An extension of the compensator allows for a high speedLock-in amplifier free amplitude demodulation, which is used for topography imaging with the firstresonance. A different technique for improving material property sensitivity is presented basedon structural modifications of the cantilever. Focused Ion Beam milling is used to remove massfrom specific areas in the cantilever such that the first and higher eigenmodes are tuned towardseach other. The shape and location of mass removal is determined either by simulation beforehandor through an in-situ approach. Higher harmonics of the harmonic active cantilevers indicate asignificant response of up to 10% in respect to the first resonance/harmonic