Direct Digital Synthesis Method Research Articles

Physical work principles of digital computational synthesizers of multiphase signals

Modern systems of radio engineering systems are very widely used in radar and radio communications. An important component of the work of radio systems is the creation of diagnostic equipment with high resolution, noise immunity, improved security and reliability, which become more accessible with the advent of digital computer frequency synthesizers. Digital computer synthesizers using the direct digital signal synthesis method are the main nodes of modern diagnostic equipment for radar and radio communication systems. The article considers a number of advantages of digital computing synthesizers, which include a wide range of synthesized frequencies, an extremely small step of the frequency grid, extremely fast frequency tuning speed, phase continuity during frequency tuning, low phase noise, a simple algorithm for generating complex signals, the possibility of independent amplitude control, phase and frequency of the synthesized signal. The principles of construction and structural and circuitry solutions of digital computational synthesizers based on the method of direct digital synthesis of frequencies and signals are given. The principle of constructing structures of digital multiphase signal synthesizers is proposed, in which the initial phases of the synthesized signals can be set in software. Structural diagrams of digital computational synthesizers based on digital code storage devices and with an M-shaped law of frequency variation which allow synthesizing signals with amplitude, frequency and phase modulation in the frequency range from 0.001 to 400 MHz are presented.

Application high-speed digital-to-analog converters for direct digital synthesis of high-frequency radio signals

The main features of high-speed digital-to-analog converters designed for direct digital synthesis of radio frequency signals in the UHF and microwave ranges are presented. A block diagram of a digital signal generator based on high-speed DACS is proposed. These DACs are designed to create digital signal generators that work based on the direct digital synthesis method. The main specialized modes of operation of high-speed digital-to-analog converters that allow efficient use of extra components of the spectrum are studied. Images of the main frequency of synthesis occur when the signal is restored from digital to analog form. Special operating modes of high-speed DACS allow you to create broadband and ultra-wideband signals. The use of high-speed digital-to-analog converters in special modes of operation makes it possible to simplify the block diagrams of digital signal generator. The scheme is simplified by reducing the number of cascades of the output frequency multipliers.

Primary Standard of the Unit of Frequency Deviation. New Opportunities and Prospectives

The possibility of expanding working frequency ranges and increasing the precision of State Primary Special Standard of the unit of frequency deviation GET 166–2004 is considered. Methods and means of measuring the frequency deviation that may be incorporated into the improved GET 166–2004 are proposed. Results of studies of the following four independent methods of measuring frequency deviation are presented: method of electronic computer frequency meter; method of direct digital synthesis; method of Bessel function zeros; and method of measuring the extremal values of the period.

Features of direct digital synthesis applications for microwave excitation signal formation in quantum frequency standard on the atoms of cesium

Features of direct digital synthesis applications in quantum frequency standard on the atoms of cesium are considered. A new design of a frequency synthesizer based on direct digital synthesis method and magnetic field stabilization system are presented. Experimental research of frequency synthesizer showed improvement parameters of a microwave excitation signal, such as step frequency tuning, time frequency tuning, range of generating frequencies and spectral characteristics. Magnetic field stabilization system eliminates one of the most important perturbing factors affecting on long-term frequency stability. Experimental research of metrological characteristic of quantum frequency standard showed improvement long-term frequency stability by 15%.

Study of Phase Shift Control in High-Speed Ultrasonic Vibration Cutting

High-speed ultrasonic vibration cutting (HUVC) applies an ultrasonic vibration to a cutting tool transverse to the cutting direction. The advantage of this method is that the high-speed cutting exceeds the critical cutting speed restrictions of ultrasonic vibration cutting. However, irregular dimple arrays are machined on the work-piece surface, increasing the surface roughness. In this paper, a phase shift control method is proposed, which aims to overlap dimples in a regular pattern to decrease the surface roughness for HUVC. First, this paper investigates the theory of phase shift control to guarantee the surface quality of HUVC. Then, a closed-loop direct digital synthesis (DDS) system is designed to keep the phase shift of the machined dimples stable and controllable. A contrast experiment is conducted to compare the performance of the closed-loop DDS and the open-loop DDS methods in HUVC process. The results show that the closed-loop DDS method can render the dimple phase stable and controllable during the HUVC process. The phase shift value influences the surface roughness. Setting the phase shift to 0.94π with an appropriate feed-rate, the surface roughness is reduced to 0.303, compared to a surface roughness of 0.785 when using the open-loop DDS method.

The main metrological characteristics of generators on the basis of a method of direct digital synthesis of signals

The main metrological characteristics of generators on the basis of a method of direct digital synthesis of signals

Low Cost Laboratory Type Signal Generator Using DDS Method

Everyone who is an amateur or student interested in electricity or electronics needs a signal generator that can produce different types of signals that must be located at the front edge. This requirement can often be met by equipment in the laboratories or signal generators received at high prices under the project. This study focuses on the design of a low cost signal generator having high accuracy and sensitivity. In previous studies, DDS (Direct Digital Synthesis) method was implemented with FPGA and other high cost microcontrollers. With this study, the design of the high-accuracy signal generator has been made simpler and more cost-effective thanks to the PIC microcontroller, which can be found easily in the market. The device designed in the study is a digital signal generator that produces sine, triangle and square wave which are created using decimal numbers in the microcontroller and converted to analog signal via DAC (Digital to Analog Converter). Also, the digital potentiometer on the device, which is used as feedback in the circuit, allows us to control the output signal. This study provides a solution for producing a low cost laboratory type signal generator having high sensitivity, however this solution is not a new method. Satisfactory results have been achieved from the implementation circuit.

New microwave excitation signal generating circuit for quantum frequency standard on the atoms of caesium Cs133

In this work the study, design, development and experimental results of a new microwave excitation signal generating circuit are presented. New design of this circuit is based on the method of direct digital synthesis. The results of theoretical calculations and experimental researches show that the new design not only has a high precision, but also has an improvement in the spectral characteristics of the output signal. Range of generated output frequencies is expanded, that leads to the possibility of detuning the frequency of the neighboring resonance of spectral line and adjust the C-field in quantum frequency standard. Experimental research of the metrological characteristics of the quantum frequency standard on the atoms of caesium with a new functional unit showed an improvement in the daily frequency stability.

Dependence of microwave-excitation signal parameters on frequency stability of caesium atomic clock

New scheme of the microwave – excitation signal for the caesium atomic clock is based on method of direct digital synthesis. The theoretical calculations and experimental research showed decrease step frequency tuning by several orders and improvement the spectral characteristics of the output signal of frequency synthesizer. A range of generated output frequencies is expanded, and the possibility of detuning the frequency of the neighboring resonance of spectral line that makes it possible to adjust the C-field in quantum frequency standard is implemented. Experimental research of the metrological characteristics of the quantum frequency standard on the atoms of caesium – 133 with new design scheme of the microwave – excitation signal showed improvement in daily frequency stability on 1.2*10-14.

New means of generating a low-frequency sine-wave signal with a low harmonic distortion coefficient and the problems of providing metrological backup

The problem of constructing precision apparatus for generating a sine-wave signal based on the direct digital synthesis method is considered. A block diagram and the basic technical characteristics are presented, and the individual units of the G3-135, G3-136, and G3-137 generators, the harmonic distortion coefficients of which are less than 0.001%, are described. The results of tests of the generators at the achieved value of the harmonic distortion coefficient are presented.

A Reinforcement-Learning-Based Fuzzy Compensator for a Microcontroller-Based Frequency Synthesizer/Vector Voltmeter

This paper presents the development of an intelligent fuzzy-based compensation scheme, utilizing reinforcement learning methodology, which can be used to compensate the reading of an unknown voltage, in vector form. This compensator is implemented online, in real time, with an indigenously developed microcontroller-based scheme that can be used both as a frequency synthesizer and as a vector voltmeter. This frequency synthesizer/vector voltmeter is developed using a direct digital synthesis method for the frequency synthesizer and a synchronous detection technique for the vector voltmeter. The developed fuzzy compensator has been tested in both offline and online modes, and in both cases, it has been found to significantly improve the accuracy of the measurement compared to those obtained with an uncompensated vector voltmeter. It has been shown that the final compensated measurements are in close agreement with the true unknown voltages under measurement.

Direct digital synthesis based - function generator with digital signal modulations

This paper focuses on signal generation with digital modulations, especially on the possibility of using the direct digital synthesis method. The specific structure of the function generator is explained. The developed construction is designed as a laboratory device. Realization enables to operate this device in two ways, via the user interface in the PC through the USB bus or by the display and keypad located directly on the product. Furthermore, this paper deals with results of measurement digital modulation generating, signal distortion and the test measurement in frequency and time domain.

Optical-fiber finger photo-plethysmograph using digital techniques

This paper presents digital techniques to design an optical-fiber photo-plethysmograph. This noninvasive method is based on the measurement of the intensity of an infrared-light beam, which penetrates the index finger. Sinusoidal modulation of the light-beam by driving an infrared LED is proposed. The method of direct digital synthesis is used to produce a very stable sinusoidal waveform. Optical fibers are used to transfer the light to and from the sampling point. Synchronous amplitude demodulation is used here instead of using analog low-pass filters, so the information concerning the amplitude is almost noiseless. Off-line frequency analysis of the peripheral volume pulse-wave signal is performed. The power content in the harmonics of this pulse wave may be a useful measure of aging and vascular disease.

Suspended sediment and dye concentration measurements using a digital technique

This paper presents a new digital technique for measuring the concentration of the suspended sediment and dye materials in fluids. The method is based on the measurement of the attenuation of a sinusoidally modulated light beam penetrating a small sample volume of the fluid. The method of direct digital synthesis is used to produce a sine wave in the input stage, giving a high stability in the amplitude and frequency of the light-beam modulating waveform. This sinusoidal waveform drives six infrared or colour light emitting diodes, depending on the material to be detected. The system facilitates optical fibres to transfer the optical signal to and from the sampling point. The collected light is converted through photodiodes to an attenuated sinusoidal electrical signal. In contrast to the conventional optical sediment detection devices, here synchronous amplitude demodulation is used instead of conventional analogue low-pass filters. Therefore, the information concerning the amplitude is pure and a very high signal to noise ratio can be achieved. The use of a sinusoidal waveform instead of rectangular pulses having high harmonic content results in less influence on the receiver from higher frequencies. The above improvements resulted in a high resolution instrument.

A low-cost wide-frequency-range three-phase sine-wave signal generator using direct digital synthesis technique

This design note describes a three-phase sine-wave signal generator. The waveforms are digitally synthesized by using three weighting resistor networks and high-speed CMOS switches. The phase differences between the three sine waves are kept precisely at 120 degrees . This low-cost direct digital synthesis method provides excellent amplitude and frequency stability, small distortion and a wide frequency range, up to 3.3 MHz.

A general purpose differential digital modulator implementation incorporating a direct digital synthesis method

A highly versatile digital modulator that uses a direct digital synthesis method to perform signal modulation is described. In contrast to the customary methods of implementing I-Q modulation schemes utilizing in-phase and quadrature branches, this design approach is based on directly accessing many of the digitally stored carrier modulating symbols according to the information bearing input signals. Apart from the digital-to-analog converter, all the previous stages are digital. To demonstrate the concept, a differential 16-QAM modulator was implemented. The technique lends itself to VLSI implementation. It can be considered as a digital implementation of a digital modulator. >

A digital interface for phase control of PTS-300 synthesizers

Modern NMR spectrometers must be equipped to generate accurate, fast, reproducible radiofrequency phase shifts of essentially arbitrary angles under pulse programmer control. Many designs for phase shifting circuits have been used: analog circuits using delay lines ( I), RC networks (2)) hybrid networks (3)) digital designs based on clocked logic (4-7) or packaged phase shift units (S), high-speed analog designs using double-balanced mixers (9), and circuits using direct digital synthesis (DDS) techniques. The DDS designs using lookup tables have other advantages such as rapid phase-continuous frequency switching. Adding a phase shift option to such a circuit is relatively straightforward. Digital frequency synthesizers produced by Programmed Test Sources, Inc., are popular with designers of NMR spectrometers. In our homebuilt spectrometer we have used two PTS-300 synthesizers equipped with the “Type 2” frequency generation scheme that allows phase shifts in 0.225’ steps (2n/ 1600) using the DDS method. In this Note we describe a simple interface that allows the phase shift options of the PTS to be implemented in a convenient way. The design has the advantage that it allows the step size of the phase shifts to be preset, so that phase shifts can be expressed in multiples of a basic increment rather than in multiples of the basic resolution. The design can readily be adapted to other situations where such a feature is desirable. The PTS-300 uses 12 binary lines to encode the phase shift. Four lines specify the phase shift in multiples of 0.225” using binary coded decimal (BCD), and another four lines specify the phase shift in multiples of 2.25”, also using BCD. The final 4 lines specify the phase shift in multiples of 22.5”, but in contrast to the other lines, these 4 are coded in binary in the range 0 to 15 ,0 (in the older models the top 4 lines are also in BCD, giving 0.36” resolution). The relation between the desired phase shift and the requisite binary code is thus rather involved, although of course

Design and flight testing of digital direct side-force control laws

Three-input/three-output command augmentation control laws have been designed and tested in flight using Princeton's Variable-Response Research Aircraft. Controllers were based upon algebraic model-following, a fast and efficient method of direct digital synthesis for advanced control modes. Pilot opinions of several command modes and controller-to-command pairings are presented in this paper. Flat turns, lateral translation, and roll control were investigated. Of the command modes tested, foot pedals-to-yaw rate, lateral stick-to-roll rate, and thumb lever-to-sideslip angle provided the best overall ratings.