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EN
The paper presents a novel implementation of a time-to-digital converter (TDC) in field-programmable gate array (FPGA) devices. The design employs FPGA digital signal processing (DSP) blocks and gives more than two-fold improvement in mean resolution in comparison with the common conversion method (carry chain-based time coding line). Two TDCs are presented and tested depending on DSP configuration. The converters were implemented in a Kintex-7 FPGA device manufactured by Xilinx in 28 nm CMOS process. The tests performed show possibilities to obtain mean resolution of 4.2 ps but measurement precision is limited to at most 15 ps mainly due to high conversion nonlinearities. The presented solution saves FPGA programmable logic blocks and has an advantage of a wider operation range when compared with a carry chain-based time coding line.
EN
This work shows a time-domain method for the discrimination and digitization of parameters of voltage pulses coming from optical detectors, taking into account the presence of electronic noise and afterpulsing. Our scheme is based on an FPGA-based time-to-digital converter as well as an adjustable-threshold comparator complemented with commercial elements. Here, the design, implementation and optimization of a multiphase TDC using delay lines shorter than a single clock period is also described. The performance of this signal processing system is discussed through the results from the statistical code density test, statistical distributions of measurements and information gathered from an optical detector. Unlike dual voltage threshold discriminators or constant-fraction discriminators, the proposed method uses amplitude and time information to define an adjustable discrimination window that enables the acquisition of spectra.
EN
The paper describes the construction, operation and test results of three most popular interpolators from a viewpoint of time-interval (TI) measurement systems consisting of many tapped-delay lines (TDLs) and registering pulses of a wide-range changeable intensity. The comparison criteria include the maximum intensity of registered time stamps (TSs), the dependency of interpolator characteristic on the registered TSs’ intensity, the need of using either two counters or a mutually-complementing pair counter-register for extending a measurement range, the need of calculating offsets between TDL inputs and the dependency of a resolution increase on the number of used TDL segments. This work also contains conclusions about a range of applications, usefulness and methods of employing each described TI interpolator. The presented experimental results bring new facts that can be used by the designers who implement precise time delays in the field-programmable gate arrays (FPGA).
EN
We presents the design and test results of a picosecond-precision time interval measurement module, integrated as a System-on-Chip in an FPGA device. Implementing a complete measurement instrument of a high precision in one chip with the processing unit gives an opportunity to cut down the size of the final product and to lower its cost. Such approach challenges the constructor with several design issues, like reduction of voltage noise, propagating through power lines common for the instrument and processing unit, or establishing buses efficient enough to transport mass measurement data. The general concept of the system, design hierarchy, detailed hardware and software solutions are presented in this article. Also, system test results are depicted with comparison to traditional ways of building a measurement instrument.
EN
The paper presents the design of a microprocessor system intended for control, data processing and communication in a multi-channel time counter. The time counter is a relatively complex autonomous instrument designed for measurements of time with picosecond precision and frequency within a range of 3.5 GHz. The device employs a high-speed, single-chip microcontroller with event-driven programming without the mediation of an operating system. The autonomous operation of the measurement system with real-time controlling and data processing was achieved. The paper focuses on the hardware design and the software development model which enables collision-free and concurrent work of many components. The device uses advanced mechanisms available in STM32 series microcontrollers, allowing the efficient support for USB and Ethernet interfaces. The microprocessor system works at a relatively low frequency, which minimizes emission of interference and allows measuring time intervals with a high precision.
EN
The paper presents a concept of utilization of counter-timer circuits built in popular microcontrollers for generating precise time intervals. The main aim was to generate pulses START and STOP wholly in hardware without using a core of the microcontroller. This enables minimizing the value of time jitter of the generated time intervals and allows the use of remaining resources of the microcontroller freely. The introduced method of generation exploits the possibility of simultaneous synchronization of TIM2 and TIM3 timers from an overloaded TIM1 timer. Dependent timers work in One Pulse Mode. START and STOP signals are generated by PWM channels of individual timers. PWM channels can be configured independently which gives the possibility to generate START and STOP pulses of different polarity and width. Generation of a time interval can be triggered automatically (TIM1) or through one of the inputs of the microcontroller. The implemented generator is characterized by the generated range of time interval from 0 to 100 s and the resolution of 40 ns. The jitter of 100 ps was obtained. The concept is suitable to apply in any microcontroller of the STM32 family. It allows the generation of precise and adjustable delays in the application without the need to significantly expand a hardware part of the device.
PL
Przedstawiono budowę, zasadę działania i wyniki badań wielokanałowego modułowego licznika czasu. Umożliwia on równoczesny pomiar relacji czasowych pomiędzy impulsami wejściowymi (START), pochodzącymi z maksymalnie sześciu niezależnych źródeł zegarowych, a wspólnym dla wszystkich kanałów impulsem odniesienia (STOP). Moduły pomiarowe licznika wykonano z użyciem układów programowalnych FPGA Spartan-3 (Xilinx). Licznik charakteryzuje się zakresem pomiarowym do 1 s oraz precyzją pomiarów nie gorszą niż 250 ps.
EN
We present the design, operation and test results of a modular multichannel time counter built with the use of programmable devices. Its resolution is below 50 ps and the measurement range reaches 1 sec. The design of the counter is shown in Fig. 1. It consists of six independent measurement modules. Each measurement module contains a 2-channel time interval counter (Fig. 2) implemented in a general-purpose reprogrammable device Spartan-3 (Xilinx). To obtain both high precision and wide measurement range, the counting of periods of a reference clock is combined with a two-stage interpolation within a single period of the clock signal [6]. The interpolation involves a four-phase clock in the first interpolation stage [8] and a time delay coding line in the second interpolation stage. The reference clock module contains an integrated digital synthesizer [7], that provides the reference clock signal of 250 MHz for measurement modules, and is driven by an external clock source of 5 MHz or 10 MHz. The standard measurement uncertainty of the time counter was tested (Figs. 3 and 4) carefully and it did not exceed 250 ps in the full measurement range. As the acid test of the time counter, the differences between signals of 1 PPS from the tested clock sources and the reference 1 PPS signal were also verified (Figs. 5 and 6). The modular design makes the multi-channel time counter easy to modify to meet requirements of various applications.
8
Content available Ultrasonic flow measurement with high resolution
EN
The ultrasonic flowmeter which is described in this paper, measures the transit of time of an ultrasonic pulse. This device consists of two ultrasonic transducers and a high resolution time interval measurement module. An ultrasonic transducer emits a characteristic wave packet (transmit mode). When the transducer is in receive mode, a characteristic wave packet is formed and it is connected to the time interval measurement module inputs. The time interval measurement module allows registration of transit time differences of a few pulses in the packet. In practice, during a single measuring cycle a few time-stamps are registered. Moreover, the measurement process is also synchronous and, by applying the statistics, the time interval measurement uncertainty improves even in a single measurement. In this article, besides a detailed discussion on the principle of operation of the ultrasonic flowmeter implemented in the FPGA structure, also the test results are presented and discussed.
EN
The designing process of high resolution time interval measurement systems creates many problems that need to be eliminated. The problems are: the latch error, the nonlinearity conversion, the different duty cycle coefficient of the clock signal, and the clock signal jitter. Factors listed above affect the result of measurement. The FPGA (Field Programmable Gate Array) structure also imposes some restrictions, especially when a tapped delay line is constructed. The article describes the high resolution time-to-digital converter, implemented in a FPGA structure, and the types of errors that appear there. The method of minimization and processing of data to reduce the influence of errors on the measurement is also described.
PL
W artykule opisane są projekt i wyniki badań przetwornika czas-liczba o rozdzielczości 5,3 ps (1 LSB) i zakresie pomiarowym 428 ps. Do przetwarzania czasowo-cyfrowego użyta została metoda kodowania wielokrotnego. Metoda ta umożliwia pokonanie ograniczeń technologicznych współczesnych układów scalonych i uzyskanie wartości rozdzielczości mniejszej niż czas propagacji pojedynczej komórki linii kodującej. Przetwornik został zrealizowany w układzie programowalnym Spartan-6 firmy Xilinx.
EN
This paper presents the implementation and tests results of a time-to-digital converter based on the wave union method and implemented in Spartan-6 FPGA (Xilinx). The converter has the resolution of 5,3 ps (1 LSB) in the measurement range of 428 ps and the integral nonlinearity of 3,8 LSB (Fig. 7). In the wave union method, contrary to the typical conversion methods with a single coding, the resolution is lower than the FPGA cell delay thanks to coding several transitions of the time event signal (Fig. 2). In addition, the linearity of conversion is increased by reducing the width of wide bins. Although, using a multi-transition pattern gives better performance, it also brings more problems to be solved. The main problems such as implementation of a pattern generator for certain amount of transitions, minimal delays between transitions and elimination of bubble errors are discussed in this paper. The pattern generator (Fig. 3) is implemented with use of a carry chain. It enables controlling the pattern by means of diagnostic and measurement software. Bubble errors (Fig. 4) are eliminated with a fast asynchronous encoder (Fig. 5). The diagnostic-control software (Fig. 6) allows to configure the pattern generator, launch the measurement session and generate a text file with all information needed to calculate conversion characteristics of the time-to-digital converter.
EN
This paper describes a design and test results of time interval counter (TIC), which provides a high precision of 14.4 ps within a wide measurement range of 1 ms. To achieve these parameters the counting method with a two-stage interpolation within a single clock period is involved. A subgate delay resolution is obtained with the aid of the differentia delay line technique. To diminish the nonlinearities of conversion and finally to improve the precision of measurement a novel matrix of differential delay lines is proposed. The TIC is implemented as an Application Specific Integrated Circuit (ASIC) in 0.35 µm CMOS process.
PL
W artykule przedstawiono projekt i wyniki badań licznika czasu o precyzji pomiaru 14.4 ps i zakresie pomiarowym powyżej 1 ms. Osiągnięcie wysokiej precyzji i szerokiego zakresu pomiarowego było możliwe dzięki zastosowaniu metody licznikowej i dwustopniowej interpolacji. Zastosowanie różnicowej linii kodującej w drugim stopniu interpolacji pozwoliło osiągnąć rozdzielczość pomiaru mniejszą niż opóźnienie pojedynczego bufora. Zaproponowana matryca kodująca z różnicowymi liniami kodującymi zmniejsza nieliniowość konwersji i w efekcie zwiększa precyzję pomiaru odcinka czasu. Licznik czasu zaprojektowano i wykonano w technologii CMOS 0.35 µm jako układ specjalizowanych (ASIC).
EN
This paper describes the design and test results of a time-to-digital converter with 1.9 ps resolution and measurement uncertainty below 12.2 ps (Fig. 4). The time-to-digital conversion is based on time width averaging. Information about the measured time interval is contained in the width of a pulse that circulates in a closed delay loop and its width is measured by the counting method with use of a high frequency multiphase clock (Fig. 1). The converter resolution is directly proportional to the number of cycles of the measured pulse in the delay loop, the number of phases and frequency of a clock used (2). However, increase in the number of loop cycles causes growth in the jitter of circulating pulse edges that finally leads to deterioration in the measurement precision. Therefore, in order to obtain the highest precision of conversion, the number of cycles for which the converter provides the smallest measurement uncertainty was experimentally determined. In addition, to minimize a disadvantageous impact of unequal propagation times of the loop elements for the rising and falling pulse edges on the value of the measured time interval, the information about the measured time interval is contained between the rising edges of the pulse-pair instead of the opposite (rising and falling) edges of a single pulse (Fig. 2). The converter was implemented in a programmable device Spartan-6 manufactured by Xilinx. (Xilinx).
13
Content available Quantization error in time-to-digital converters
EN
Methods of time interval measurement can be divided into asynchronous and synchronous approaches. It is well known that in asynchronous methods of time-interval measurement, uncertainty can be reduced by using statistical averaging. The motivation of this paper is an investigation of averaging in time interval measurements, especially in a synchronous measurement. In this article, authors are considering the method of averaging to reduce the influence of quantization error on measurement uncertainty in synchronous time-interval measurement systems, when dispersion of results, caused by noise is present. A mathematical model of averaging, which is followed by the results of numerical simulations of averaging of measurement series is presented. The analysis of results leads to the conclusion that in particular conditions the influence of the quantization error on measurement uncertainty can be minimized by statistical averaging, similar to asynchronous measurements.
PL
Przepływomierze ultradźwiękowe mierzące różnicę czasu przelotu impulsu przez medium stanowią jedną z dwóch najbardziej rozpowszechnionych grup przepływomierzy. W artykule tym została przedstawiona konstrukcja systemu pomiaru odcinka czasu zaimplementowanego w strukturze programowalnej FPGA jak również metoda kalibracji i wyznaczenia rozdzielczości przetwornika czas/cyfra w trakcie pomiaru. Takie rozwiązanie zapewnia niewrażliwość układu na czynniki zewnętrzne (temperatura), oraz skrócenie czasu pomiaru, a tym samym redukcję poboru energii, co jest atutem przy zasilaniu bateryjnym.
EN
The ultrasonic flowmeter market is the fastest-growing market in any flowmeter type, and transit-time flowmeters have the largest share in that market. One of the fundamental parts of a transit-time ultrasonic flowmeter is a time measurement circuit, often implemented in CMOS ASIC. This paper describes an application of a low-power FPGA device to the transit-time flowmeter time measurement circuit. The main problem discussed in this work is calibration of a delay line in TDC implemented in a FPGA device. The time- and resource-consuming code density testing is undesirable for mass production devices. In this paper a fast and simple method for calibration is proposed. The method is based on measurement of the clock period length [5] and analysis of the data; therefore, it does not require implementation of any additional circuits in the device. A resolution of TDC is estimated by (2), when I_T is the largest state of a decoder in measurement series, and T_0 is clock period. The method uncertainty is larger than that of the code density test, but the method requires virtually no resources and takes less time - under certain conditions the calibration can be performed simultaneously with the measurement. At the end the measurement results and the conclusions are presented.
PL
W artykule zaprezentowano nową metodę autonomicznej układowej korekcji błędu nieliniowości przetwornika czas-cyfra opartego na noniuszowej linii opóźniającej. Wyniki symulacji pokazały, że możliwe jest zmniejszenie błędów nieliniowości o rząd wielkości. W symulacji Monte Carlo dla szesnastokomórkowej linii noniuszowej zaprojektowanej w technologii CMOS 0.35 m i średnim opóźnieniu komórki wynoszącym 10 ps, otrzymano błędy nieliniowości sumacyjnej INL mniejsze niż 1 ps.
EN
The paper presents a new autonomous nonlinearity error correction method for vernier delay line (VDL, Fig. 1) based time-to-digital converter (TDC). The described VDL consists of flip-flops and two delay chains. The first chain is composed of voltage controlled delay buffers (Fig. 3a) and the second one utilizes digitally controlled shunt capacitor scheme (Fig. 3b). In order to accomplish nonlin-earity correction both delay chains in VDL are first set to the same delay using voltage controlled buffers, then the delays of buffers in both chains are compared with use of flip-flops and adjusted with shunt capacitor controlled buffers. Finally, once more the voltage controlled buffers are used to increase VDL delay and achieve the needed LSB. The simulations show that nonlinearity error reduction by an order of magnitude is possible with this method. Monte Carlo simulations performed with 16 stages VDL (CMOS 0.35 m) indicate that integral nonlinearity (INL) error can be less than 1 ps (Fig. 4b). Some predictions about max INL error based on time model are also presented. Moreover, nonmonotonic VDL can also be corrected, which improves attainable resolution. In opposition to the previously proposed VDL calibration methods[1, 3, 4, 5, 6], there is no need for either implementing accurate signal sources or generating a large number of uncorrelated time events like in the code density method.
PL
W artykule opisane są projekt i wyniki badań konwertera czasowo-cyfrowego o rozdzielczości 9 ps i niepewności pomiarowej nie przekraczającej 31 ps. Konwerter został zrealizowany w układzie programowalnym Cyclone firmy Altera. Do konwersji czasowo-cyfrowej użyto nowatorskiej metody, w której informacja o mierzonym odcinku czasu zawarta jest w szerokości impulsu, propagującego się wielokrotnie w zamkniętej pętli opóźniającej i próbkowanego z użyciem wielofazowego zegara o wysokiej częstotliwości. Sterowanie procesem pomiarowym oraz obliczanie i przetwarzanie wyników pomiarów odbywa się z wykorzystaniem dedykowanego interfejsu użytkownika opracowanego w języku C++.W artykule opisane są projekt i wyniki badań konwertera czasowo-cyfrowego o rozdzielczości 9 ps i niepewności pomiarowej nie przekraczającej 31 ps. Konwerter został zrealizowany w układzie programowalnym Cyclone firmy Altera. Do konwersji czasowo-cyfrowej użyto nowatorskiej metody, w której informacja o mierzonym odcinku czasu zawarta jest w szerokości impulsu, propagującego się wielokrotnie w zamkniętej pętli opóźniającej i próbkowanego z użyciem wielofazowego zegara o wysokiej częstotliwości. Sterowanie procesem pomiarowym oraz obliczanie i przetwarzanie wyników pomiarów odbywa się z wykorzystaniem dedykowanego interfejsu użytkownika opracowanego w języku C++.
EN
The paper describes the design and test results of a time-to-digital converter with 9 ps resolution and measurement uncertainty below 31 ps. The converter has been implemented in a programmable device Cyclone manufactured by Altera. The time-to-digital conversion is based on sampling of a periodic square signal. Information about the measured time interval is contained in the width of a pulse that circulates in a closed delay loop and is sampled with the use of a high frequency clock. This method is innovative in the kind of application and it has not been implemented in an integrated circuit so far. In order to achieve both high resolution and high measurement uncertainty the four-phase sampling clock has been used. Such solution allows for fourfold reduction in a number of cycles in the loop and consequently to diminish the measurement error significantly. The four-phase clock has been generated with an embedded PLL functional block. An issue of fundamental importance for the successful implementation of the converter was the use of two short pulses as a representation of the begin and the end of a measured time interval instead of a single long-width pulse. In this way an unpredictable shrinking or stretching of a measured time interval by elements of the delay loop that have different propagation times for rising and falling edges has been avoided. The measurement as well as calculation and processing of obtained results are controlled with the use of dedicated user interface worked out in C++.
PL
Jedną z zasadniczych części przepływomierza ultradźwiękowego jest układ elektroniczny mierzący czas przejścia impulsu pomiędzy przetwornikami ultradźwiękowymi. Minimalna wartość mierzonego strumienia przepływu zależy od rozdzielczości pomiaru czasu. W referacie przedstawiono metody pomiaru czasu w przepływomierzach ultradźwiękowych wykorzystujących metodę pomiaru odcinka czasowego. W szczególności przedstawiono koncepcję układu scalonego CMOS dedykowanego do pomiaru czasu w przepływomierzach ultradźwiękowych, mających zastosowanie w pomiarach małych strumieni przepływu.
EN
One of a most important parts of ultrasonic flowmeter is electronic circuit, which measures transit time of the ultrasonic signals. Minimal value of measured flow rate depends on resolution of time-to-digital converter. In this paper methods of time-interval measurement in ultrasonic flowmeter are described. Implementation of chosen method in CMOS technology is discussed. Expected quantization error of time-to-digital converter is 174 ps and expected resolution of transit - time measurement using sing-around method is 15 ps.
PL
W artykule przedstawione są projekt i wyniki badań konwertera czas-liczba o rozdzielczości 78 ps i niepewności pomiarowej poniżej 100 ps. Pomiar czasu realizowany jest z użyciem 32 liczników zliczających okresy szesnastofazowego zegara o częstotliwości 400 MHz. Ponieważ aktywne są obydwa zbocza zegara jest on równoważny pojedynczemu sygnałowi zegarowemu o częstotliwości 12.8 GHz, co umożliwia osiągnięcie średniej rozdzielczości ok. 78 ps przy interpolacji jednostopniowej. Budowa opisanego konwertera czasliczba pozwala na łatwe rozszerzanie zakresu pomiarowego, wynoszącego 164 žs, poprzez zwiększanie pojemności użytych liczników dwójkowych. Sterowanie procesem pomiarowym oraz wyznaczanie i przetwarzanie wyników pomiarów odbywa się z użyciem dwóch procesorów programowych NIOS II zintegrowanych z konwerterem w układzie programowalnym Stratix II firmy Altera.
EN
This paper describes design and test results of the time-to-digital converter with 78 ps resolution and accuracy below 100 ps. The time interval measurement is performed with the use of 32 binary counters counting periods of 16-phase clock of the 400 MHz frequency. Since both edges of the clock are active it is an equivalent of a single clock signal of 12.8 GHz frequency, which provides a mean resolution of about 78 ps in a single interpolation stage. The structure of the converter allows to extend its measurement range (164 žs) easily by increasing the capacity of used binary counters. The measurement as well as calculation and processing of obtained results are controlled by two soft-core processors NIOS II implemented together with the converter in a single programmable device from family Stratix II (Altera).
PL
Przedstawiono problemy projektowe dotyczące implementacji odwrotnościowej metody pomiaru częstotliwości w układzie FPGA. Analizowane są sposoby osiągania wysokiej dokładności przy relatywnie krótkim czasie trwania pomiaru, minimalizacji wartości czasu martwego, maksymalizacji częstotliwości powtarzania pomiarów oraz efektywnym szacowaniu miar statystycznych. Zaprezentowano wyniki badań karty pomiarowej z układem programowalnym Spartan3 (Xilinx), w którym zintegrowane zostały kompletny licznik czasu, pamięć FIFO i układ sterujący.
EN
This paper describes the design problems concerning implementation of the reciprocal method of a frequency measurement in an FPGA device. The following problems are examined: ways of reaching the high accuracy with a relatively short measurement time, minimization of the dead time, maximization of the frequency of measurement repetition, and effective calculation of statistics. Test results of a computer card for frequency measurement are presented. The card is equipped with the precise time counter integrated together with FIFO memory and a control system in the Spartan3 device (Xilinx).
PL
W artykule przedstawione są projekt i wyniki badań konwertera czas-liczba o rozdzielczości 75 ps i zakresie pomiarowym 5.5 ns. Konwerter został zrealizowany w układzie programowalnym Spartan3 firmy Xilinx. Do konwersji czasowo-cyfrowej zastosowano metodę skracania impulsu. W konwerterze wykorzystano cyfrowy detektor zboczy impulsu, który umożliwia kontrolowanie wartości rozdzielczości i uniezależnia mierzony czas trwania impulsu od niekorzystnego wpływu linii transmisyjnych i programowalnych matryc połączeniowych.
EN
This paper describes design and test results of the time-to-digital converter with 75 ps resolution and 5.5 ns measurement range. The converter is implemented in a single programmable device from family Spartan3 (Xilinx). The pulse-shrinking method is used for time-to-digital conversion. Digital pulse-edges detector is applied to control of the conversion resolution and to do measured width time of pulse independent from disadvantageous influence of transmission lines and programmable switch matrixes.
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