Papers by David Humphreys
2016 87th ARFTG Microwave Measurement Conference (ARFTG), 2016
The Nonlinear Vector Network Analyzer (NVNA) is the workhorse for nonlinear measurements. Also, d... more The Nonlinear Vector Network Analyzer (NVNA) is the workhorse for nonlinear measurements. Also, during the development of new communications systems, such as 5G, dedicated test equipment is not available. Sampling and real-time oscilloscopes offer a lower cost alternative to the NVNA but require error corrections to improve their accuracy. NPL, NIST and other NMIs have advanced this area and we summarize these corrections and their limitations, with examples, and set out guidance rules to maximize the accuracy of the results.
Proc. 43-nd Meeting of the Wireless World Research Forum (WWRF)",, Oct 10, 2019
We overview the 3-year Meteracom project which will provide traceability to the SI for THz commun... more We overview the 3-year Meteracom project which will provide traceability to the SI for THz communication measurement parameters. The key objectives are to develop new metrological methods to characterize the measurement systems, system components and propagation channels. The final objective is to develop metrology for functionality and signal integrity of THz communication systems; particularly device discovery and beam tracking, determination of physical layer parameters for digital transmission and real-time performance evaluation.
Technical Digest: Symposium on Optical Fiber Measurements, 2004., 2004
Optical Aulomatic Network Analyzers extend ihe use of the traditional microwave inslrument to mea... more Optical Aulomatic Network Analyzers extend ihe use of the traditional microwave inslrument to measure the modulation response of optoelectronic components such as receivers and transmitters. The issues of lineariiy, opiical coherence and polarization are explored.
2018 Conference on Precision Electromagnetic Measurements (CPEM 2018), Jul 1, 2018
Using a recently-developed time-of-flight measurement technique with 1 ps time resolution and ele... more Using a recently-developed time-of-flight measurement technique with 1 ps time resolution and electron-energy spectroscopy, we developed a method to measure the longitudinal-optical-phonon emission rate of hot electrons travelling along a depleted edge of a quantum Hall bar. A comparison of the experimental results to a single-particle model implies that the main scattering mechanism involves a two-step process via intra-Landau-level transition. We show this scattering can be suppressed by controlling the edge potential profile, and a scattering length > 1 mm can be achieved, allowing the use of this system for scalable single-electron device applications.
2018 Conference on Precision Electromagnetic Measurements (CPEM 2018), Jul 1, 2018
Using a recently-developed time-of-flight measurement technique with 1 ps time resolution and ele... more Using a recently-developed time-of-flight measurement technique with 1 ps time resolution and electron-energy spectroscopy, we developed a method to measure the longitudinal-optical-phonon emission rate of hot electrons travelling along a depleted edge of a quantum Hall bar. A comparison of the experimental results to a single-particle model implies that the main scattering mechanism involves a two-step process via intra-Landau-level transition. We show this scattering can be suppressed by controlling the edge potential profile, and a scattering length > 1 mm can be achieved, allowing the use of this system for scalable single-electron device applications.
A reflectometer technique using scalar optoelectronic measurements has been proposed to correct s... more A reflectometer technique using scalar optoelectronic measurements has been proposed to correct source mismatch errors. The merits of different detector configurations and the measurement system requirements have been discussed. A GaInAs photodiode has been measured to 40 GHz using a DFB laser heterodyne system. Results corrected for source mismatch using reflection coefficient measurements have been compared with results measured by the reflectometer technique. Agreement between the two corrected optoelectronic responses is better than 0.2 dB.
Frequency-Stabilized Lasers and Their Applications, 1993
This paper reports experimental work towards a laboratory standard based on the 20Ne transition a... more This paper reports experimental work towards a laboratory standard based on the 20Ne transition at 1.523 micrometers , some calibration measurements to 2.5 parts in 107 on lines of C2H2 between 1.52 and 1.545 micrometers , and investigation of a standard at 1.56 micrometers involving a CO line. Progress is described towards measurement of the latter line by frequency doubling to, and beating against, a Rb D2-line stabilized laser at 0.780 micrometers of known frequency.
Traceable calibrations of high-speed communications test equipment face challenges. The propagati... more Traceable calibrations of high-speed communications test equipment face challenges. The propagation of uncertainty from primary waveform standards is achieved using a covariance matrix approach, which becomes impractical as the waveform data length increases. We present a method where the covariance data stays at acceptable level. The method is described and an example with real measured data is given.
2012 Conference on Precision electromagnetic Measurements, 2012
ABSTRACT This paper describes measurement of inter-channel timing errors for two Digital Sampling... more ABSTRACT This paper describes measurement of inter-channel timing errors for two Digital Sampling Oscilloscope designs. Timebase correction algorithms compensate the main error component ±15 ps but a channel specific residual term of up to ±4 ps remains.
The traceability route for phase-standards is outl ined together with a preliminary compression a... more The traceability route for phase-standards is outl ined together with a preliminary compression algorithm that allows the uncertainties, represented as a covariance matr ix, to be efficiently stored so that they may be represented in either the time or frequency domains The final algorithm will be available on the Euramet IND016 website. Comb generators, uncertainties, covariance matrix, nonlinear measurements, sampling oscilloscope, phase measurements.
2018 Conference on Precision Electromagnetic Measurements (CPEM 2018)
This paper proposed a prime number algorithm to avoid embedded errors when using Digital Real-Tim... more This paper proposed a prime number algorithm to avoid embedded errors when using Digital Real-Time Oscilloscope to calibrate a multi-tone stimulus harmonic phase reference. Measurement results are presented to verify the validity of the frequency selection algorithms.
IEEE Transactions on Microwave Theory and Techniques
This paperWe have investigateds the baseband measurement techniques of the nonlinear vector netwo... more This paperWe have investigateds the baseband measurement techniques of the nonlinear vector network analyzer (NVNA) test bench, aiming to fully characterize the behaviors of RF power amplifiers and mixers under complex modulation. In order to involve the baseband measurement, two kinds of NVNA phase reference approaches are developed as alternative solutions, so that the baseband phase measurements can be synchronized with those of modulated components at fundamental and harmonic bands. In the first case, a modulated baseband signal is combined with another modulated multi-harmonic one to become the desired NVNA phase reference. While in the other case, a sweeping multisine is used as the primary phase reference, and assisted by an auxiliary one to obtain equivalently static NVNA phase measurements. To validate the proposed NVNA test bench, an RF power amplifier is tested by applying a large-signal LTE-like multisine drive, whose multi-band output measurements are compared with that using an oscilloscope. Moreover, an RF mixer is used as a second type of device under test to explore the application of this work.
IEEE Transactions on Microwave Theory and Techniques
A simple diode-based Nonlinear Verification Device (NVD) design for Nonlinear Vector Network Anal... more A simple diode-based Nonlinear Verification Device (NVD) design for Nonlinear Vector Network Analyzers is presented together with an improved Figure of Merit (FOM) parameter that is insensitive to impedance match and isolates variation of the device's nonlinear parameters. The stability over 84 hours and load-pull performance of this new design have been evaluated.
RF Waveform metrology provides a traceable link between the CW RF primary standards, the primary ... more RF Waveform metrology provides a traceable link between the CW RF primary standards, the primary electrical risetime standards and the complex RF test-equipment used in the wireless communications industry. The advantages and limitations of different instrument types are compared. Examples are shown of modulation waveform uncertainty calculation and choice of RF filter for pulsed RF transition duration.
The latest generation of precision modulation sources are reaching accuracies that test the limit... more The latest generation of precision modulation sources are reaching accuracies that test the limits of existing measurement equipment. ISO 17025 is a major driver for traceability requirements. We describe a new sampling-oscilloscope based technique to measure the AM and PM components of a modulated RF signal. This method offers the possibility of extracting all AM and PM components from a single measurement. Nonlinearities within the system are explicit and quantifi able and analysis of the data provides both the results and their uncertainties.
31st European Conference on Optical Communications (ECOC 2005), 2005
ABSTRACT Intrinsic noise of optical jitter measuring receivers can be characterized by using a ji... more ABSTRACT Intrinsic noise of optical jitter measuring receivers can be characterized by using a jitter-free optical calibration pattern. We report a method for producing a 10Gb/s NRZ optical calibration pattern with measured pk-pk jitter
Formation-flying studies to date have required continuous and minute corrections of the orbital e... more Formation-flying studies to date have required continuous and minute corrections of the orbital elements and attitudes of the spacecraft.This increases the complexity, and associated risk, of controlling the formation, which often makes formation-flying studies infeasible for technological and economic reasons. Passive formation-flying is a novel space-flight concept, which offers a remedy to those problems. Spacecraft in a passive formation are allowed to drift and rotate slowly, but by using advanced metrology and statistical modelling methods, their relative positions, velocities, and orientations are determined with very high accuracy. The metrology data is used directly by the payloads to compensate for spacecraft motions in software. The normally very stringent spacecraft control requirements are thereby relaxed, which significantly reduces mission complexity and cost. Space-borne low-frequency radio astronomy has been identified as a key science application for a conceptual p...
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Papers by David Humphreys