4,392 research outputs found

    Phase imaging with intermodulation atomic force microscopy

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    Intermodulation atomic force microscopy (IMAFM) is a dynamic mode of atomic force microscopy (AFM) with two-tone excitation. The oscillating AFM cantilever in close proximity to a surface experiences the nonlinear tip-sample force which mixes the drive tones and generates new frequency components in the cantilever response known as intermodulation products (IMPs). We present a procedure for extracting the phase at each IMP and demonstrate phase images made by recording this phase while scanning. Amplitude and phase images at intermodulation frequencies exhibit enhanced topographic and material contrast.Comment: 6 pages, 6 page

    Multipath Polyphase Circuits and their Application to RF Transceivers

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    Nonlinearity and time-variance in radio frequency (RF) circuits leads to unwanted harmonics and intermodulation products, e.g. in power amplifiers and mixers. This paper reviews a recently proposed multipath polyphase circuit technique which can cancel such harmonics and intermodulation products. This will be illustrated using a power upconverter IC as an example. The upconverter works from DC to 2.4 GHz, and the multipath polyphase technique cleans its spectrum up to the 17th harmonic, keeping unwanted spurious responses more than 40dB below the carrier. The technique can also be useful for other applications, and some possible applications will be discussed

    Multi-tone EMC testing strategy for RF-devices

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    In low-cost miniaturized electronic systems, filters are often omitted in front of active non-linear components, potentially resulting in unwanted intermodulation products in the band of operation. Current immunity tests most often use a single-frequency source and are hence not able to capture all relevant intermodulation products. Relying on an anechoic chamber as test facility and using multiple-tone excitation from a dual-source network analyzer, we present an advanced test methodology to evaluate in-the-band leakage of out-of-band undesired frequencies. To demonstrate our approach we use a frequency-selective active textile antenna with integrated non-linear low-noise amplifier

    Interplex modulation and a suppressed-carrier tracking loop for coherent communications systems

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    Simple addition to hardware and new mode of operation of transmitter and receiver in coherent, PCM/PSK/PM configuration greatly improves channel efficiency. Procedure reduces amount of power lost to intermodulation products

    Intermodulation distortion in a directly modulated semiconductor injection laser

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    A most important quantity in high-frequency analog transmission is the intermodulation distortion product. Experimental studies of the third order intermodulation distortion products in the modulation response of high-speed semiconductor lasers give very low values (< −60 dB) at low frequencies, an increase at a rate of 40 dB/dec as the modulation frequency is increased, and a leveling off at one-half of the relaxation oscillation resonance frequency. These experimental results can be well explained by a theory based on a perturbative analysis of laser dynamics

    Electromagnetic compatibility aware design and testing of intermodulation distortion under multiple co-located sources illumination

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    Current electromagnetic immunity tests mainly rely on single-frequency sources. However, the evolution of electronic systems leads to miniaturisation and low-cost solutions, in which filters are omitted in front of active non-linear components, also for efficiency reasons. As a result, intermodulation products may leak into the band of operation. The authors propose a comprehensive strategy consisting of design and test methodologies to evaluate in-the-band leakage of out-of-band undesired components, using multiple-tone excitation and relying on an anechoic chamber as test facility. The aim of this study is to demonstrate that an anechoic chamber together with a dual-source network analyser represents an optimal facility to investigate signal integrity issues owing to leakage of intermodulation products

    Distortion Cancellation via Polyphase Multipath Circuits

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    The central question of this paper is: can we enhance the spectral purity of nonlinear circuits with the help of polyphase multipath circuits. Polyphase multipath circuits are circuits with two or more paths that exploit phase differences between the paths to cancel unwanted signals. It turns out that it is very well possible to cancel distortion products produced by a nonlinear circuit. Unfortunately, there are also some spectral components that cannot be cancelled with the polyphase multipath circuits. In this paper tables are presented that can easily be used to predict which spectral components are cancelled and which are not cancelled for a certain polyphase multipath circuit

    Intermodulation distortion in high dynamic range microwave fiber-optic links with linearized modulators

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    Linearization of integrated optic intensity modulators significantly reduces the two-tone intermodulation distortion. The resulting intermodulation distortion produced by these modulators then varies as the input power to the fifth-order link system, the overall intermodulation product is a combination of third-order and higher-order terms. The authors determine the dynamic range of a cascaded microwave network consisting of a preamplifier, a high-dynamic-range fiber-optic link with a highly linear modulator, and a postamplifier. An expression is found that relates the intermodulation power at the output to the relative suppression from the signal level. As an example, a hypothetical 10-GHz low-distortion fiber-optic link that has a dynamic range of 125 dB in a bandwidth of 1 Hz is cascaded with various preamplifiers, and it is shown that the dynamic range of the system is reduced by as much as 20 dB, depending on the third-order intercept of the amplifier

    The Role of Nonlinear Dynamics in Quantitative Atomic Force Microscopy

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    Various methods of force measurement with the Atomic Force Microscope (AFM) are compared for their ability to accurately determine the tip-surface force from analysis of the nonlinear cantilever motion. It is explained how intermodulation, or the frequency mixing of multiple drive tones by the nonlinear tip-surface force, can be used to concentrate the nonlinear motion in a narrow band of frequency near the cantilevers fundamental resonance, where accuracy and sensitivity of force measurement are greatest. Two different methods for reconstructing tip-surface forces from intermodulation spectra are explained. The reconstruction of both conservative and dissipative tip-surface interactions from intermodulation spectra are demonstrated on simulated data.Comment: 25 pages (preprint, double space) 7 figure

    Spectral Purity Enhancement via Polyphase Multipath Circuits

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    The central question of this paper is: can we enhance the spectral purity of nonlinear circuits by using polyphase multipath circuits? The basic idea behind polyphase multipath circuits is to split the nonlinear circuits into two or more paths and exploit phase differences between these paths to cancel undesired distortion products.\ud It turns out that it is very well possible to use polyphase multipath circuits to cancel distortion products produced by a nonlinear circuit. Unfortunately, there are also some spectral components that cannot be canceled with the polyphase multipath circuits
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