Direct Digital Synthesis Chip Research Articles

Precise, portable and wide band alternating current source for extremely low current values

Alternating current (AC) sources which provide currents in micro ampere ranges have become essential for testing of electronic components, simulation of sensors, eddy current analysis, small signal analysis of transistors, electro-cutaneous stimulation in therapeutics, current injection in medical imaging techniques etc. This manuscript proposes a precise voltage mode AC source for extremely low current values. A simple AC source with load in the feedback is optimised experimentally by compensating the capacitive effects (approx. 4.7 pF) by employing a novel combination of general impedance converter (gic) or Negative Capacitance Converter (NCC) circuits along with basic circuit. The design is proposed with precise value of 160 $$\upmu A$$ for applications including physiological measurements. It is seen that GIC circuit modification offers better consistency and performance in load analysis compared to NCC. Load analysis (10–2000 $$\Omega$$), frequency analysis (100 Hz to 1 MHz), stability analysis and reliability testing confirm the optimised and precise operation of the proposed current source. With very high degree of matching in theoretical and practical results, calculation of output impedance is also done and the value is fair enough. The hardware incorporates direct digital synthesis chip driven by a microcontroller for generation of sine wave, thereby reducing the need of bulky power supplies and function generators. This precise alternating current source is suitable for wide band portable applications.

A hybrid analog-digital phase-locked loop for frequency mode non-contact scanning probe microscopy

Non-contact scanning probe microscopy (SPM) has developed into a powerful technique to image many different properties of samples. The conventional method involves monitoring the amplitude, phase, or frequency of a cantilever oscillating at or near its resonant frequency as it is scanned across the surface of a sample. For high Q factor cantilevers, monitoring the resonant frequency is the preferred method in order to obtain reasonable scan times. This can be done by using a phase-locked-loop (PLL). PLLs can be obtained as commercial integrated circuits, but these do not have the frequency resolution required for SPM. To increase the resolution, all-digital PLLs requiring sophisticated digital signal processors or field programmable gate arrays have also been implemented. We describe here a hybrid analog/digital PLL where most of the components are implemented using discrete analog integrated circuits, but the frequency resolution is provided by a direct digital synthesis chip controlled by a simple peripheral interface controller (PIC) microcontroller. The PLL has excellent frequency resolution and noise, and can be controlled and read by a computer via a universal serial bus connection.

Low distortion signal generator based on Direct Digital Synthesis for ADC Characterization

<p class="Abstract"><span lang="EN-US">This paper presents a low distortion signal generator with a frequency range from 0 to 10 kHz using the direct digital synthesis (DDS) method for ADC characterization. The results show that the maximum distortion in the whole frequency range is -80.37 dB, the frequency resolution is 1.421 nHz (with a 48-bits DDS chip), the stability in frequency is 25 µHz/Hz and the amplitude stability is 13 µV/V.</span></p>

Design of an arbitrary waveform signal generator

Signal generator plays a very important role in communication, electronic measuring instruments, electronic circuits, automatic control, radar and other electronic systems. Direct Digital Synthesis (DDS) technology can easily control the frequency of the signal for direct synthesis of waveforms. This paper designed a signal generator with the amplitude and frequency modulation by using AD9850 as frequency synthesizer and AT89S52 single chip microcomputer (SCM) as the core. Detailed design principle and idea are discussed. AD9850 of the DDS chip is used to generate the waveform. The frequency data of external input can be transformed to frequency phase control words of chip by simple parallel or serial communication interface with the single chip microcomputer. Amplitude modulation is realized by the AD7520 chip. The system is not only simple in structure, easy to implement, but also convenient and cheap. It has a theoretical and practical value.

A radio-frequency source using direct digital synthesis and field programmable gate array for nuclear magnetic resonance

A radio-frequency (rf) source for nuclear magnetic resonance (NMR) is described. With the application of direct digital synthesis (DDS), the rf source has the ability to yield rf pulses with short switching time and high resolution in frequency and phase. To facilitate the generation of a soft pulse, a field programmable gate array (FPGA) cooperating with a pulse programmer is used as the auxiliary controller of the DDS chip. Triggered by the pulse programmer, the FPGA automatically controls the DDS to generate soft pulse according to predefined parameters, and the operation mode of the pulse programmer is optimized. The rf source is suitable for being used as transmitter in low-field (<1 T) NMR applications, for example, magnetic resonance imaging and relaxation measurement. As a compact and low-cost module, the rf source is of general use for constructing low-field NMR spectrometer.

An accessible electrical impedance tomograph for 3D imaging

A new electrical tomograph that is designed specifically for low-cost and accessibility is described. It offers a unique environment for three-dimensional (3D) electrical impedance imaging. Using a cross-bar switch, the hardware can support ad hoc measurement strategies and is linked to control software, which integrates the complete process from 3D finite element modelling through to image reconstruction and generation of movie files. Digital signal processing algorithms are used to derive measurements of complex impedance from the measurement of amplitude and phase difference between the driven and received signals. This is achieved by rapid sampling of sinusoidal signals having frequencies between 1.0 Hz and 1.0 MHz. The instrument can deliver about 100 measurements per second, corresponding to a typical 16-electrode tomography frame, and is targeted at processes with modest dynamics or for laboratory development of tomographic applications and algorithms. The latest version (LCT2) is described here and uses a USB2 link to provide data transfer rates up to 20 MBytes per second. Sinusoidal excitation signals are derived using a direct digital synthesis chip. Voltage measurements are digitized to 16-bit accuracy and the standard system can accommodate 64 electrodes. The software embraces the EIDORS-3D soft-field reconstruction algorithms and the resulting impedance imaging capability of the device and characterization of the signals are described.

A DDS Waveform Generator for Electromagnetic Non-Destructive Testing

A direct digital synthesis (DDS) waveform generator for electromagnetic non-destructive testing (NDT) is presented in order to improve the measurement quality. The advantage and disadvantage of analogue and digital circuit waveform generators are analyzed. The DDS technique is preferred. The principle of DDS technique is introduced and the hardware and software design of a DDS waveform generator is described. The characteristics of the waveform generator based on a DDS chip AD7008 are that the signal frequency is of high stability, high precision and high resolution. Furthermore, the amplitude, frequency and phase can be continuously adjusted. An experimental electromagnetic NDT system is built and the testing results are analyzed. The system uses digitally generated sine waves as exciting, reference and demodulation signals. Experimental results show that the DDS waveform generator improves the signal-to-noise ratio. This kind of wave generation circuit is used not only in NDT but also in other instruments, such as electrical impedance tomography (EIT), which need signals with high stability, high precision and high resolution.

A complete digital radio-frequency source for nuclear magnetic resonance spectroscopy

A complete digital radio-frequency source suitable for broadband nuclear magnetic resonance applications is described. The use of a complete direct digital synthesis chip makes the design not only as a frequency- and phase-continuous tunable radio-frequency source, but also as an arbitrary wave form generator. This rf source is capable of generating a signal with frequency from dc up to 135 MHz directly. The whole design is mounted on a printed circuit board that can be inserted into one of the industry standard architecture slots in the personal computer and is controlled by the software. Details about the implementation and characteristics of the whole design are discussed in this article.

A digital approach to an FM exciter

A digital approach to an FM exciter is presented that provides several advantages over previous analog techniques. This approach, called direct digital frequency modulation (DDFM), is centered around a direct digital synthesis (DDS) chip which allows true digital generation of the FM signal. The DDS chip is a perfectly linear modulator with superior phase-noise characteristics over the current analog voltage-controlled oscillator (VCO) approach. The DDS modulator drives a low-noise phase-locked loop (PLL) which allows upconversion to any FM channel without manual tuning. The exciter demonstrates superior microphonics immunity by separating the frequency tuning from the modulation path, thus allowing wider PLL bandwidths. The exciter can accept either the existing composite analog format or can interface with future digital sources.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>