Digital Waveform Generator Research Articles

ISRO's programmable digital waveform generator

One of the major and common requirements for all active microware sensors is generation of the transmit modulation signal-like chirp/LFM signal, MSK, etc., which can be generated by analog or digital means. With the increasing demands of side bandwidth, longer duration chirp signals in radar systems, digital signal generation, and processing has emerged as a preferred alternative. Design and development of programmable and generic digital waveform generator (DWG) system based on Xilinx Virtex XCV600 FPGA and high-speed DAC is carried out at the Space Applications Center. ISRO is to generate required transmit chirp signal of high time-bandwidth product (~ 1000) for ISO's microwave radar sensor missions. This gives a detailed description of the design requirements, implementation details, salient performance features, and test results of this programmable and generic digital waveform generator (DWG).

Multi-frequency EIT system with radially symmetric architecture: KHU Mark1

We describe the development of a multi-frequency electrical impedance tomography (EIT) system (KHU Mark1) with a single balanced current source and multiple voltmeters. It was primarily designed for imaging brain function with a flexible strategy for addressing electrodes and a frequency range from 10 Hz–500 kHz. The maximal number of voltmeters is 64, and all of them can simultaneously acquire and demodulate voltage signals. Each voltmeter measures a differential voltage between a pair of electrodes. All voltmeters are configured in a radially symmetric architecture in order to optimize the routing of wires and minimize cross-talk. We adopted several techniques from existing EIT systems including digital waveform generation, a Howland current generator with a generalized impedance converter (GIC), digital phase-sensitive demodulation and tri-axial cables. New features of the KHU Mark1 system include multiple GIC circuits to maximize the output impedance of the current source at multiple frequencies. The voltmeter employs contact impedance measurements, data overflow detection, spike noise rejection, automatic gain control and programmable data averaging. The KHU Mark1 system measures both in-phase and quadrature components of trans-impedances. By using a script file describing an operating mode, the system setup can be easily changed. The performance of the developed multi-frequency EIT system was evaluated in terms of a common-mode rejection ratio, signal-to-noise ratio, linearity error and reciprocity error. Time-difference and frequency-difference images of a saline phantom with a banana object are presented showing a frequency-dependent complex conductivity of the banana. Future design of a more innovative system is suggested including miniaturization and wireless techniques.

X-band experimental airborne radar – Phase II: synthetic aperture radar and ground moving target indication

Defence Research and Development Canada, Ottawa, has completed Phase II of a multifunction X-band wideband experimental airborne radar. The system consists of a high average power transmitter, a digital waveform generator, two wideband 8-bit channels for synthetic aperture radar (SAR)/inverse synthetic aperture radar and two narrowband 14-bit channels for ground moving target indication (GMTI). The reflector antenna uses a novel multimode feedhorn to derive two phase centres displaced in azimuth. The radar was designed to support research into SAR imaging of fixed and moving targets (ocean and land), time–frequency analysis of moving targets, clutter suppression for GMTI radar and ocean surveillance for small and large target detection. Highlights of the data collection capabilities, include a swath width 16 K points wide in the single-channel SAR modes, 8 K points wide in the two-channel integrated SAR–GMTI modes and 4 K points wide in the GMTI surveillance modes. The architecture of the radar, its modes of operation with respect to the SAR and GMTI data collection capabilities, the MATLAB-based GMTI processor, and the real-time kernel developed for the SAR processor are discussed; and results from its high resolution stripmap, landspot, seaspot and GMTI modes are presented from trials in July 2003.

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.

Wavelength modulation absorption spectroscopy with 2 f detection using multiplexed diode lasers for rapid temperature measurements in gaseous flows

Multiplexed fiber-coupled diode lasers are used to probe second-harmonic line shapes of two near-infrared water absorption features, at 1343 nm and 1392 nm, in order to infer temperatures in gases containing water vapor, such as combustion flows. Wavelength modulation is performed at 170 kHz, and is superimposed on 1-kHz wavelength scans in order to recover full second-harmonic line shapes. Digital waveform generation and lock-in detection are performed using a data-acquisition card installed in a PC. An optimal selection of the modulation indices is shown to greatly simplify data interpretation over extended temperature ranges and to minimize the need for calibration when performing 2 f ratio thermometry. A theoretical discussion of this optimized strategy for 2 f ratio thermometry, as well as results from experimental validations in a heated cell, at pressures up to atmospheric, are presented in order to illustrate the utility of this technique for rapid temperature measurements in gaseous flow fields.

A pseudorandom pink noise for the computer-based measurements of linear responses

We propose a nonbinary pseudorandom sequence for the measurement of linear responses. Compared with a maximal length shift register sequence (m sequence), this sequence is more suitable for digital processing based on computers; with the use of discrete Fourier transforms, the response functions are reproduced without approximations from digitally sampled data because the input power spectrum is pink, i.e., completely flat in a given frequency range and 0 otherwise. In practice, the new sequence is simply the sum of harmonics with arbitrary phases and is produced readily with digital wave form generators. For reducing the peak power of this sequence, the amplitude distribution is better to be bimodal rather than Gaussian. For demonstrating its feasibility with common digital hardware, the magnetic resonance of Rb atoms in a sub-MHz region was measured successfully. With the use of the fast Fourier transform algorithm, our software task was only 0.4% of that for the cross-correlational calculation based on an m sequence.

Musical tone electronic synthesizer and method

A tone generator (501) for a musical synthesizer has digital waveform generators (602,603) arranged such that a proportion of an output from a waveform generator (602) is supplied to a phase modulating input of a next waveform generator (603), wherein a proportion of the output from the last waveform generator in a chain (603) of serially connected waveform generators is supplied to a phase modulating input of the first waveform generator (602) in said chain, thereby providing a degree of recursion. Outputs from a plurality of waveform generators are supplied to a ring modulator (604) for generating harmonic sums and differences of frequencies produced by said recursion. A variable precision waveform lookup table (803) may be used to select a particular harmonic characteristic of tone and a frequency doubler (1001) may be included in the feedback loop to enable tones containing predominantly odd harmonics to be generated.

Equipment for selective excitation in NMR spectroscopy: enhanced techniques for radio-frequency modulation and digital pulse-shape generation

This paper describes readily constructed electronic equipment for generating shaped pulses for use in nuclear magnetic resonance spectroscopy. A radio-frequency modulator is controlled by the analogue waveshape supplied by a digital waveform generator. The modulator makes use of a double-balanced mixer in a circuit, which extends its linear range. Both the modulator and the digital section embody enhancements over conventional techniques. The equipment was designed to be integrated into Bruker spectrometers controlled by ASPECT computers; modification to accept data from other machines should not involve major changes. The analogue output of the waveform generator could also be used to control field gradient pulse shapes.

Optimal waveform selection for tracking systems

Investigates adaptive waveform selection schemes where selection is based on overall target tracking system performance. Optimal receiver assumptions allow the inclusion of transmitted waveform specification parameters in the tracking subsystem defining equations. The authors give explicit expressions for two one-step ahead optimization problems for a single target in white Gaussian noise when the tracker is a conventional Kalman filter. These problems may be solved to yield the most improvement possible in tracking performance for each new transmitted pulse. In cases where target motion is restricted to one dimension, closed-form solutions to the local (one step ahead) waveform optimization problem have been obtained. The optimal waveform selection algorithms in the paper may be included with conventional Kalman filtering equations to form an enhanced Kalman tracker. Simulation examples are presented to illustrate the potential of the waveform selection schemes for the optimal utilization of the capabilities of modern digital waveform generators, including multiple waveform classes. The extension of the basic waveform optimization scheme to more complex tracking scenarios is also discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

New aspects of rotational field and flux measurement in electrical steel

A system for measurement of rotational power loss is described comprising a 2-channel digital waveform generation, a 4-channel data acquisition board and gain controlled amplification circuitry. This paper also describes the theory, development and testing of a simple and accurate means of measuring localised rotational flux density which avoids the need to drill holes in samples for search coils. The results of measurements on non-oriented, grain-oriented and amorphous material are presented and the difference between the measured rotational loss for clockwise and anticlockwise rotation of the flux is discussed.

Wide-range oscillator with digital control for digital waveform generation

A variable frequency oscillator with precise digital control over a very wide frequency range has been developed. Two standard VCO chips are used to form two independent phase-locked loops; one adjusted to cover the lower frequency range and the other the higher frequency range. A simple decoder circuit selects the output from the appropriate VCO and also ensures a smooth crossover in the intermediate frequency range. The output is synchronised with a low frequency reference input and is ideally suited for use as a clock in variable frequency digital sinewave generation circuits.

A 270-kb/s 35-mW modulator IC for GSM cellular radio hand-held terminals

The modulator IC is a mixed analog/digital transceiver component in a chip set that is designed for the hand-held terminals of the pan-European 900-MHz Groupe Special Mobile (GSM) digital cellular radio network. The concept of the radio-frequency environment in which the circuit is used is explained, focusing on the differences in existing systems. The architecture and different functions of the modulator circuit and details of the digital and analog processing in the transmission mode are discussed. The receiving mode, which is mostly based on analog processing, is highlighted. The device generates Gaussian minimum-shift-keying (GMSK) modulation and converts the received signal to 8-b words after filtering. The modulator IC uses digital waveform generation and a quadrature signal representation. This device is implemented in a 1.5- mu m CMOS technology. The power consumption is less than 35 mW from a 5-V supply.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Programmable digital waveform generator

The transputer is useful not only as a parallel processing element, but also as an embedded controller. The paper describes a digital waveform generator based on the transputer. By executing a program written in a high-level language, a transputer aided by a single-chip counter generates complex digital signals with precise state times ranging from 200 ns to infinity in 50 ns increments. The duration of each output state is determined by data rather than by program execution speed: this simplifies programming. Repetition and concatenation of sequences of output states may also be encoded into data structures, which are interpreted by an invariant program. The transputer is controlled with a single serial link, and is easily integrated into a network of transputers or any system capable of communicating with a byte serial protocol. The control of focal plane arrays for astronomy is presented as a demonstration of the flexibility of the device. Fabrication cost, size and power consumption are greatly reduced relative to traditional bit-slice designs.

Digital waveform generation by fractional addressing.

This article concerns the generation of waveforms by a digital oscillator in which sampled data in a memory buffer are recycled. The buffer contains a fixed waveform and the output sample rate is also fixed. Despite these constraints, the oscillator is capable of arbitrarily high frequency resolution if the technique of fractional addressing is used. However, fractional addressing introduces distortion. This article gives a theory of fractional addressing, resembling the theory of diffraction in crystal lattices with a basis. The theory shows how the spectrum of the distortion components can be calculated and how the distortion can be minimized. Attention is called to numerous symmetries in the distortion spectrum. These symmetries are especially interesting if the purpose of the system is to make use of the distortion components to create inharmonic signals. Of particular importance is the gamma p symmetry theorem, which makes it possible to derive simple formulas for the level of the largest distortion component and for the total distortion power.

A low-cost 10-channel S-100 compatible counter-timer circuit

A 10-channel counter-timer circuit designed to monitor the rates of particle detectors is presented. It utilises two Am9513 'System Timing Controller' chips together with ancillary logic and is compatible with the IEEE-Std-696/S-100 computer bus. Input signals of up to 6.9 MHz on 10 twisted-pair lines can be counted with 16-bit accuracy. Alternatively, the circuit can be reconfigured by software to form two 80-bit counters. It is also capable of a wide range of time interval measurements, sequencing and digital waveform generation.

System for testing wattmeters under nonsinusoidal conditions

Electrical and electronic power meters, due to nonlinear principles of operation, can exhibit, under nonsinusoidal conditions, errors that are not predictable from their frequency characteristic. A minicomputer-based calibration system to produce such test conditions is described. It relies on a two-phase digital arbitrary waveform generator as a waveform source and on a sampling rms/power meter as a monitoring instrument. At 120-V 5-A sinusoidal operation the “phantom” power can be reproduced with accuracy ±100 ppm at 50 or 60 Hz and ±200 ppm for frequencies up to 1 kHz.

A Precision Phase Angle Calibration Standard for Frequencies up to 50 kHz

A Phase Angle Calibration Standard covering a frequency range from 2 Hz to 50 kHz has been designed and constructed. Digital waveform generation is used to provide sinusoidal analog outputs having precisely settable phase angles. Output voltages are independently adjustable from 0.5 to 100 V rms on both channels. An auto-zero feed back loop compensates for differential phase errors of the output amplifiers.

An acoustic pulse generator for wind instrument bores

An inexpensive piezoelectric transducer described earlier [M. I. Ibisi and A. H. Benade, J. Acoust. Soc. Am. Suppl. 1 72, S63 (1982)] is driven by an arbitrary (digital) waveform generator. The width and shape of the volume velocity pulse generated are controlled by Wiener (least‐mean‐squares) filtering [A. C. Holly, J. Acoust. Soc. Am. 75, 973–976 (1984)]. Using a Harming pulse, or one cycle of a raised sinusoid, we have examined the reflected and transmitted waves that arise at simple discontinuities in bores. One particularly unusual result is an exponentially growing wake in the pressure response to a volume velocity pulse generated at the closed large end of a cone. This wake is required to satisfy the conservation of mass in a closed system, as is also the case for the exponentially decaying wake that arises at the closed small end of a cone [R. D. Ayers, L. J. Eliason, and D. Mahgerefteh, J. Acoust. Soc. Am. Suppl. I 74, S29 (1983).]

Long duration aperiodic musical waveform generator

First Page

Digital waveform generator having constant signal to noise ratio

An electronic musical instrument includes a p-bit memory sequentially storing the resolution contributing bits of a sequence of n-bit samples, the n-bit sequence representing a percussive-type waveform. The p-bit memory is sequentially addressed with each stored sample being suitably scaled for reestablishing the magnitudes of the corresponding n-bit samples, the scaled samples being coupled through a digital to analog converter for producing an output signal representing the percussive waveform and having a uniform signal to quantizing noise ratio.