Direct Digital Synthesis Technique Research Articles

Quadrature direct digital frequency synthesis using fine-grain angle rotation technique

An area- and power-efficient quadrature direct digital frequency synthesis technique called fine-grain angle rotation is presented. To reduce the large bitwidth requirement of the angle rotation, multiple start points are introduced and the angle rotation is applied to the remaining small angle. A prototype chip occupies 0.16 mm2 in 0.25 µm 1P5M CMOS technology and consumes 90 mW at 400 MHz clock frequency, which is a significantly improved performance compared to previous state-of-the-art chips.

Analysis and design of a frequency-hopped spread-spectrum transceiver for wireless personal communications

Personal communications services (PCS) require low-power radio technologies. One such transceiver architecture employing frequency-hopped spread-spectrum techniques is presented. System features such as antenna diversity with equal-gain combining and sequential hop combining are incorporated into the transceiver design to achieve robust wireless digital data transmission over fading channels. A direct-conversion architecture from radio frequency (RF) to baseband reduces the overall power consumption by eliminating intermediate frequency (IF) components. High-rate frequency hopping with frequency-shift keying (FSK) modulation is implemented using a direct digital frequency synthesis technique. A multiplierless correlation FSK detector, suitable for direct-conversion receivers, has been designed for quadrature noncoherent detection. Robust acquisition algorithms based on energy detection and pattern matching and tracking architectures using digital phase-locked loops are also described for system synchronization. The proposed transceiver is well-suited for low-power PCS applications and other portable wireless communications.

An automatic calibrator for wattmeters with harmonic analysis capability

This paper deals with a three-phase phantom-power generator, which is designed for calibrating digital wattmeters with harmonic analysis capability. The calibration of such instruments is a critical task due to the lack of suitable calibrators. Fortunately, the calibration procedure can be limited to the first harmonic components when digital wattmeters are employed to characterise electrical machines, so that also simple calibrator design can be adopted. This paper describes a three-phase calibrator arrangement which is able to generate an arbitrary spectrum up to 5 kHz and a phantom power variable up to 3 kVA per phase. The uncertainty on the power associated to the first harmonic components is of about 0.1% in nonsinusoidal conditions. The calibrator employs a Direct Digital Synthesis technique, so that a frequency change of the output signal can be obtained without modifying the sampling frequency. Such a technique also permits to generate the frequency modulated signals that are often encountered at the output of static power converters that feed electrical machines.

Development of a SAR digital system

A data acquisition system for an airborne SAR (Synthetic Aperture Radar) was designed and implemented. DSP is used for the first time in the implementation of a SAR data acquisition system. A novel precision programmable timer using the DDS (Direct Digital Synthesis) technique was designed, built, and successfully tested to provide increased flexibility, reliability and stability.

An 0.8-μm CMOS mixed analog-digital integrated audiometric system

This paper presents a dual-channel fully integrated audiometric system, which generates the complete set of audio and control signals required for exhaustive audiometric tests. The system includes a novel signal generator, based on the direct digital synthesis technique, which fulfils the requirements of advanced audiometric tests. The proposed system faces two different problems, namely, the generation of a finely tunable pure sinewave and the generation of noise signals with a controlled spectrum. To achieve tuning capabilities down to 1 Hz at 20 kHz and 15 /spl mu/Hz at 100 Hz, a fractional division of a 40-MHz master clock based on noise-shaping techniques is performed. Moreover, for noise generation, a novel circuit based on pseudorandom sequences combined with analog switched-capacitor filters is used. The chip is fabricated in a 0.8 /spl mu/m CMOS process and occupies a 24.2 mm/sup 2/ silicon area. It consumes 45 mW from a single 5 V power supply and achieves less than -90 dB crosstalk between the channels.

Sinewave modulation for data communication by direct digital synthesis and sigma delta techniques

AbstractDirect digital synthesis and sigma‐delta techniques have been proposed in recent years to realize sinewave generators and modulators for data communication. This paper explains the basic principles behind these techniques and presents schemes which implement popular modulation methods such as frequency shift keying, phase shift keying and amplitude modulation. The schemes are mostly implemented with digital circuits. They ensure a high degree of flexibility and are fully compatible with VLSI integration technologies. Experimental results obtained on integrated semicustom devices have demonstrated the validity of this approach.

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 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

Device for rapid manipulation of frequencies in NMR

A direct digital synthesis technique has been used to accomplish rapid changes in transmitter frequency in NMR without loss of phase coherence.