Direct Digital Synthesis System Research Articles

ВИСОКОЛІНІЙНІ БАЛАНСНІ ДВОТАКТНІ ПІДСИЛЮВАЧІ ПОСТІЙНОГО СТРУМУ ІЗ НИЗКОЮ ПОХИБКОЮ ЗСУВУ НУЛЯ

It is known that push-pull DC amplifiers (PPDA), as a rule, have a high linearity of the transfer characteristic, a wide passband (hundreds of MHz and GHz units) at the level of unity gain, and a significant rate of change in the output voltage (at least thousands of volts per microsecond). Serial models of such integrated PPDA are produced by Analog Devices, Texas Instruments, Linear Technology, National Semiconductor and others. Due to the presence of these characteristics, PPDA are widely used in current-voltage, current-current, ADC, DAC, direct digital synthesis systems and multi-channel digital systems for processing and recording analog signals. Despite the high indicated static and dynamic characteristics of the PPDAs built on bipolar transistors, which have a significant additive error in the form of an input zero bias current of hundreds of nA and μA units. Often this can degrade the static parameters of these devices and systems. When the input zero bias current appears, there are basic currents of bipolar transistors in the input stages of the amplifiers. To reduce their influence in single-cycle current amplifiers, some special circuit methods are used. Which allow an order of magnitude to reduce the input zero bias current of the differential stage without affecting the bias voltage or speed. To reduce the input zero bias current in the PPDA, it was proposed to apply basic current compensation in the input stages, as well as to build the input stages on Shiklai composite transistors, which will significantly improve the accuracy of the circuit as a whole.

Високолінійний двотактний підсилювач-маштабатор струму на біполярних транзисторах із заземленим навантаженням

Traditionally, the vast majority of electrical amplifying devices are based on voltage or current amplifiers with voltage output. They are used as elements in the ADC and DAC, as well as in information-measuring and recorded systems, signal generators in direct digital synthesis systems. This is due to the well-established theory and practice of designing such amplifiers. At the same time, in some cases it is more expedient to have operational amplifiers with current output, which can work with a grounded load. Mentioned modern devices and systems are built using integrated circuits. It should be born in mind that most of the parasitic parameters of these circuits are capacitances, and the voltage according to the second switching law cannot jump abruptly on the capacitance, then the speed of the amplifying devices can be greater if all operations on the signals are performed using current amplifiers rather than voltage amplifiers. Therefore, to maximize the use of the frequency properties of bipolar transistors, it should be used as a current amplifier. A controlled current generator can be quite easily obtained on the basis of an operational amplifier by including loads in the feedback circuit, but in this case it cannot be grounded, which narrows its capabilities. It is proposed that controlled current generators with a grounded load are to be constructed on the basis of a push-pull amplifier and current mirrors included in the negative feedback circle on bipolar transistors. However, this approach is new, almost not considered in the scientific and technical literature, therefore the topic of the article devoted to the creation of highly linear push-pull amplifiers — current scalers on bipolar transistors with a grounded load is relevant. A new method for constructing controlled current-to-current generators implemented on bipolar transistors is analyzed, in which negative feedback is based on the removal of current using current mirrors. Mathematical expressions are obtained that make it possible to set the values of current amplification factors and determine the output resistance of a DC amplifier. Computer simulation of the characteristics of a DC amplifier was carried out, the results of which confirm the possibility of their use in high-precision electronic circuits, in particular in multi-bit (n = 16…20) ADCs and DACs.

Design and Study on Analog Modulation Signal Source Based on AT89C51 Microcontroller

At present, the analog signal source in a traditional sense is far away from being sufficient to meet the needs of the modern development. Besides, the emergence of the direct digital synthesis (DDS) technology brings about a new vitality to the electronics technology of the modern times. However, because of the characteristics of the digitization, the direct digital synthesis still has the problems (the limited the output frequency range and the large spurious output). For this reason, it is particularly important to solve these problems currently. In this paper, the author carries out an analysis on the circuit characteristics of the DDS system and the analog modulation signal source system, studies their performances and characteristics, and also makes a design on both software and hardware that are based on the analog circuit and AT89C51 microcontroller system. This system is mainly composed of the microcontroller control module, the frequency synthesis module and the multiplier module. The DDS frequency synthesizer can work stably and is easy to realize. Also, the high resolution of its output frequency can meet the requirements of people in the modern times.

A multi-harmonic RF system using a MA cavity

A magnetic alloy (MA)-loaded cavity has been installed in Heavy Ion Medical Accelerator in Chiba (HIMAC). A beam study with a new Direct Digital Synthesis (DDS) system has been performed. The DDS system can generate multi-harmonic RF that includes up to 3 different RF frequencies. The multi-harmonic RF is amplified by a solid state and final amplifiers. These harmonic frequencies are in the band width of the MA RF system. Beam acceleration was performed by the system, and the acceleration efficiency was improved by both dual and triple harmonic RF.

A direct digital synthesis system for acoustic wave sensors

Current designs for acoustic wave sensor system electronics are typically based on surface acoustic wave (SAW) oscillators, phase detectors, or phase-locked loops to measure changes in SAW velocity. The advantage of oscillators is a high resolution frequency output, as compared to phase detection systems which are more stable and can more easily provide amplitude information. Phase-locked loops (PLL) offer advantages of both the oscillator and phase detection systems but have the disadvantages of a fixed frequency range and the need for frequency counting circuitry. The objectives of this work were to study the performance of a direct digital synthesis (DDS) based PLL system with the advantages of a programmable frequency range, elimination of the need for frequency counting circuitry, and tolerance of large SAW sensor insertion losses. The DDS system tested had a resolution of 4 Hz and a range of 80 to 120 MHz in SAW humidity and temperature sensing applications indicating that the DDS based PLL is a practical electronic system for SAW sensors.

Using LabVIEW for the design and control of digital signal processing systems Simulation of the ultra slow extraction at COSY

For the ultraslow extraction system of the COler SYnchrotron COSY a direct digital synthesis system is being developed. LabVIEW from National Instruments has been chosen as a tool for the simulation of the digital signal processing algorithms as well as the generation of test sequences. In order to generate adjustable band-limited noise centered at a carrier frequency, alternative algorithms have been studied. LabVIEW permits the interactive variation of relevant system parameters by means of a graphical language in order to study the quality of the frequency band limitation as a function of noise parameters, digital accuracy and frequency range and to generate test sequences by means of a real-time function generator. Advantages and limitations of LabVIEW for such applications are discussed.