Nikolai Beev

The accurate measurement of resistor nonlinearity is crucial in the design of high-precision analogue circuits and instrumentation systems. This paper presents a modified Wheatstone bridge topology designed to simplify the balancing and improve harmonic sensitivity and measurement accuracy. We introduce a polynomial model to represent the voltage-dependent behaviour of the resistor under test. A mathematical framework has been developed for the modified bridge, which links the bridge output directly to the nonlinearity coefficients of the resistor under test. A prototype system was constructed, and measurements were performed on various resistor types (e.g. metal foil, thin film). The experimental results validate the proposed model with high accuracy. Furthermore, an uncertainty analysis is presented, providing a complete characterisation of the measurement system performance. The proposed technique offers a robust, sensitive, and simplified method for measuring resistor nonlinearity down to −170 dBc with a single grounded source and no special guarding techniques.

Operational amplifiers are an important ingredient of analogue electronic circuits, and their noise performance is an essential design parameter. However, at low frequencies, data provided by component manufacturers usually cover only a limited range (typically 0.1 Hz to 10 Hz). The frequencies below this range, critical for high-stability and precision circuits, such as signal conditioning stages, voltage references, or digitizing voltmeters, are rarely addressed. Therefore, it is often necessary to characterize the parts. The traditional noise measurement technique requires the amplifier to be configured for very high gain, which is seldom the way the amplifier is used. Different techniques for voltage noise density measurement are presented and compared in this paper, including two methods that allow for noise measurement with a unity gain configuration - a mode that has not been explored until now. Practical aspects required to obtain reliable results are highlighted. A side product of this work is an open-hardware design of an ultra low-noise amplifier, which can be used to measure the noise performance of operational amplifiers or resistors using regular measuring equipment readily available at universities or industrial laboratories.

An improved variant of the 10mA and 10V dc reference and transfer standard developed for use at CERN is presented. The device achieves very low noise levels at sub-Hz frequencies, which enhances the capability for performance testing of direct-current current transformers (DCCTs) for the High Luminosity Large Hadron Collider project, where good short- and mid-term stability is essential. To characterize the standard, the 10V and 10mA outputs of a single unit were tested simultaneously against two Programmable Josephson Voltage Standards at PTB-Braunschweig. The measurements show negligible low-frequency noise contribution from the internal voltage-to-current conversion, while demonstrating Allan deviation better than 0.01 μA/A on a time scale up to one day, reaching down to few nA/A for shorter measurement times. The operation of multiple paralleled units is also presented as a viable way to further decrease both current and voltage noise.

A new digitizer, the HPM7177, which is a fundamental component of the signal chain for high precision measurement of particle accelerator magnet currents, is presented. It was designed to meet the unprecedented performance requirements for new 14 kA and 18 kA power converters for the High Luminosity Large Hadron Collider project at CERN, particularly in terms of low-frequency noise and stability. To determine accurately the performance of the digitizer, which is on a similar level as state-of-the-art classical metrological equipment, we carried out a thorough characterization using the programmable Josephson voltage standard (PJVS) at PTB-Braunschweig. At its nominal full scale of 10 V, the digitizer has a white noise level of -1/2 , 1/ f noise floor ≈ 7 × 10 ^-8 V, and a 12-hour peak-to-peak stability better than 2 μV or 0.2 partspermillion(ppm). The static non-linearity from 0V to +10V is -7 level in 12 months. The digitizer operates at a fixed rate of 10 kSamples/s and can be synchronized externally. Besides qualifying HPM7177 for its application, the characterization reveals important aspects of its operation, as well as some performance limitations.

Analog-to-digital converters with resolution exceeding 20 bits are widely available today. They exist in two forms - flexible laboratory instruments and monolithic integrated circuits. We present an overview of application fields for such digitizers, the hardware architectures that implement them, and their limitations. We review the state of the art by comparing the best-performing devices reported in scientific literature, as well as those available commercially. Our focus is particularly on integrated circuit solutions, and among our aims are the disambiguation of the multiple performance metrics in use, as well as the presentation of a clear perspective on basic performance trade-offs. Finally, we provide a discussion on the future prospects for high-resolution digitizing measurement systems.

We present a highly stable bow-tie power enhancement cavity for critical second harmonic generation (SHG) into the UV using a Brewster-cut β-BaB₂O₄ (BBO) nonlinear crystal. The cavity geometry is suitable for all UV wavelengths reachable with BBO and can be modified to accommodate anti-reflection coated crystals, extending its applicability to the entire wavelength range accessible with non-linear frequency conversion. The cavity is length-stabilized using a fast general purpose digital PI controller based on the open source STEMlab 125-14 (formerly Red Pitaya) system acting on a mirror mounted on a fast piezo actuator. We observe 130 h uninterrupted operation without decay in output power at 313 nm. The robustness of the system has been confirmed by exposing it to accelerations of up to 1 g with less than 10% in-lock output power variations. Furthermore, the cavity can withstand 30 min of acceleration exposure at a level of 3 g_rms without substantial change in the SHG output power, demonstrating that the design is suitable for transportable setups.

We have developed an avalanche transistor-based pulse generator for driving the photocathode of an image intensifier, which comprises a mainly capacitive load on the order of 100 pF. The circuit produces flat-top pulses with rise time of 2 ns, FWHM of 10 ns and amplitude of tens of V at a high repetition rate in the range of tens of MHz. The generator is built of identical avalanche transistor sections connected in parallel and triggered in a sequence, synchronized to a reference rf signal. The described circuit and mode of operation overcome the power dissipation limit of avalanche transistor generators and enable a significant increase of pulse repetition rates. Our approach is naturally suited for synchronized imaging applications at low light levels.

We have developed an avalanche transistor-based pulse generator for driving the photocathode of an image intensifier, which comprises a mainly capacitive load on the order of 100 pF. The circuit produces flat-top pulses with a rise time of 2 ns, a FWHM of 10 ns, and an amplitude of tens of V at a high repetition rate in the range of tens of MHz. The generator is built of identical avalanche transistor sections connected in parallel and triggered in a sequence, synchronized to a reference rf signal. The described circuit and mode of operation overcome the power dissipation limit of avalanche transistor generators and enable a significant increase of pulse repetition rates. Our approach is naturally suited for synchronized imaging applications at low light levels.

We present the design, construction, and characterization of a multichannel, low-drift, low-noise dc voltage source specially designed for biasing the electrodes of segmented linear Paul traps. The system produces 20 output voltage pairs having a common-mode range of 0 to +120 V with 3.7 mV/LSB (least significant bit) resolution and differential ranges of ±5 V with 150 μV/LSB or ±16 V with 610 μV/LSB resolution. All common-mode and differential voltages are independently controllable, and all pairs share the same ground reference. The measured drift of the voltages after warm-up is lower than 1 LSB peak-to-peak on the time scale of 2 h. The noise of an output voltage measured with respect to ground is μV_RMS within 10 Hz–100 kHz, with spectral density lower than 3 nV Hz^−1/2 above 50 kHz. The performance of the system is limited by the external commercial multichannel DAC unit NI 9264, and in principle, it is possible to achieve higher stability and lower noise with the same voltage ranges. The system has a compact, modular, and scalable architecture, having all parts except for the DAC chassis housed within a single 19″ 3HE rack.

We have developed a thin-film fabrication process that allows for the manufacturing of Josephson-junction-based devices from the same layout data either in the VTT Technical Research Centre of Finland foundry in Espoo, Finland or in the FLUXONICS foundry at the Leibniz-Institut fur Photonische Technologien in Jena, Germany. Automated scripts are used to derive either VTT-compatible or FLUXONICS-compatible mask plates from the same layout data. Test circuits have been fabricated at both foundries from the same layout data and their correct operation verified.