A Memory-Based Direct-Digital Frequency Synthesizer for Fractional Synchronization

Direct Digital Frequency Synthesizer (DDFS) has long been perceived as a predominant solution for producing precise, variable frequency signals having very low distortion. The paper presents an epigrammatic and a comparative study of direct digital frequency synthesizers architectures. The direct digital frequency synthesizer presented are compared on the basis of two architectures namely, the read only memory (ROM) or look up table based architecture and the other co-ordinate rotation based digital computer that eliminates the usage of the large ROM based look up table. These architectures are compared in terms of the power utilization, SFDR, etc. A mixed signal ASIC designing approach is followed for the implementation approach.

Direct digital frequency synthesis (DDS) as an indispensable key technology for modern communication systems, is widely used in digital communications, satellite communications, aerospace and high-speed instrumentation. In practical applications, DDS technology is usually required to generate different kinds of communication signals. In view of the fact that there is no related research on spurious signals when DDS technology generates communication signals, this paper based on a DDS model that can generate arbitrary symbol rate communication signals, analyzes spurious signals of the structure in detail. The conclusions of this paper can be used for the spur evaluation and parameter selection in DDS engineering applications. At the same time, this paper provides a theoretical basis for the low spurious design of DDS, and has certain reference value for DDS to generate communication signals.

A ROM-less direct digital frequency synthesizer (DDFS) is implemented based on a new 8th-order polynomial approximation of a cosine function, where digital square circuits are used to realize the components of the polynomial. MATLAB tools are used to simulate the performance of the DDFS system, where the spurious free dynamic range (SFDR) is employed as the performance factor. For a DDFS with a superior quality, the higher the SFDR, the better the spectrum purity. To validate the performance of the DDFS, the Altera FPGA platform is used with Quartus II and ModelSim, where simulation results based on Verilog implementation are illustrated.

An experimental platform was developed to investigate the effects of audible sound (20 Hz to 20 MHz) on plant growth promotion, which included a microcontroller-based embedded system for audible sound adjustment and analysis. The direct digital frequency synthesis (DDFS) method was used to generate various waveforms of sound in the platform. Soundproof glass and mufflers were used to reduce background noise. The developed system was tested on various plants, including hydroponic tomatoes, celery and mung bean. The testing results showed that the developed platform could produce pure tone and mixing audible sound with high stability and accuracy, make octave analysis of the sound under experimental environments, and the background noise in the testing chamber of the platform was lower than 55 dB(A) when the compression engine was working. The developed experimental platform has a great potential on facilitating scientific research on acoustic biology effects on plants and collecting real-time experimental data. Keywords: plant growth, background noise, acoustic biology effect, direct digital frequency synthesis, sound sensor DOI: 10.3965/j.ijabe.20150805.1556 Citation: Cai W M, Zhu S M, Wang N, He H N, Ying B H. Design of an experimental platform to investigate the effects of audible sounds on plant growth. Int J Agric & Biol Eng, 2015; 8(5): 162－169.

This work presents a low power direct digital frequency synthesizer (DDFS) by using a new two-level lookup table algorithm. The algorithm uses trigonometric double angle formula to divide ROM lookup table into two parts. The ROM size of the proposed architecture is 25% less than that of conventional two-level table. The hardware complexity of the new DDFS architecture compared to the traditional two-level table DDFS can be omitted one multiplier. A synthesized 0.35-mu DDFS with a SFDR of -80dB, runs up to 100MHz and consumes 81-mW at 3.0v. The power efficiency is 0.81-mW/MHz, which represents an enhancement of more than 38% compared to the conventional DDFS

A quadrature direct digital frequency synthesizer (DDFS) was designed and implemented in a 1.2 µm CMOS process using two non-linear resistor string DACs. These DACs are used in place of the phase-to-amplitude ROM look-up tables and the linear DACs in a conventional quadrature DDFS to give a low power design. At 25 MHz clock frequency, the DDFS dissipates less than 4 mW at 3.3 V and has SFDR better than 55 dBc at low synthesized frequencies.

This paper presents an ultra-high-speed direct digital frequency synthesizer (DDS) microwave monolithic integrated circuit (MMIC) implemented in 1μm GaAs HBT technology. The DDS has the capabilities of direct frequency modulations with 8-bit frequency resolutions. Utilizing a Double-Edge-Trigger (DET) 8-stage pipeline accumulator with sine-weighted DAC based ROM-less architecture, this DDS MMIC can maximize the utilization ratio of GaAs HBT's high-speed potential. With an external clock output frequency of 5GHz, the DDS can output sine signal of up to 5GHz frequency giving an average Spurious Free Dynamic Range (SFDR) of 23.24dBc through the first Nyquist band. The DDS MMIC consumes 2.4W of DC power from a single -4.6V DC supply. Using 1651 GaAs HBT transistors, the total area of the DDS chip is 2.4 × 2.0mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

A low-power direct digital frequency synthesizer (DDFS) architecture is presented. It uses a smaller lookup table for sine and cosine functions compared to already existing systems with a minimum additional hardware. Only 16 points are stored in the internal memory implemented in ROM (read-only memory). The full computation of the generated sine and cosine is based on the linear interpolation between the sample points. A DDFS with 60-dBc spectral purity 29-Hz frequency resolution, and 9-bit output data for sine function generation is being implemented in 0.8-/spl mu/m CMOS technology. Experimental results verify that the average power dissipation of the DDFS logic is 9.5 mW (at 30 MHz, 3.3 V).

Frequency synthesizer has been used in numerous communication applications. This is acknowledged as the heart of the electronics systems. Numerically controlled oscillator (NCO) is the primary part of this frequency synthesizer, which helps in generating high precision & high frequency signal. One of the best suited methods to empower the NCO is CORDIC algorithm. CORDIC (Coordinate Rotation Digital Computer) algorithm is one of the well-known methods used for the trigonometric & arithmetic calculation and applications of digital signal processing. This algorithm can work with higher efficiency for the signal generation & hardware utilization. CORDIC architecture is used in the NCO, which is the central part of DDFS (Direct Digital Frequency Synthesis) to produce analog signal. Here in this paper, a sinusoidal waveform generator is implemented using an efficient 16-stage pipelined CORDIC architecture with a very small look-up table (LUT). The architecture is designed, and its RTL simulation is carried out using Xilinx Vivado. The purpose of the work is to improve the output frequency and the accuracy. The architecture had been implemented on a Xilinx Spatran-6 (XC6SLX9) FPGA & the final results showed that the proposed pipelined architecture is capable of generating a maximum output frequency of 157.684 MHz with less than 1% (approximately 0.34%) of error.

In this paper, we analyze the design and the possible optimization methods of the direct digital frequency synthesizer (DDFS) based on quadratic approximation. The goal is to design a DDFS with reduced hardware cost and very high spectral purity. For the DDFS based on quadratic approximation, there is a trade-off between the size of the memory and the approximation logic. We show that by exploring this trade-off, it is possible to design a DDFS which requires less hardware and features higher spectral purity than the previously presented solutions. By using the proposed design method, a DDFS that generates 16-bit sinusoidal waves with a spurious free dynamic range of 132 dBc (126 dBc if the phase is truncated) was designed.

This paper introduces a novel Direct Digital Frequency Synthesizer (DDFS) based on Complementary Dual-Phase Latch-Based digital design. Compared to conventional DDFS using Flip-Flop as synchronizing element, the proposed approach allows to double the sampling data rate while enhancing the clock skew tolerance and system latency. The design features a 24 bits pipelined Phase Accumulator (PA) and a 14×10 bits Phase to Amplitude Converter (PAC). The Phase to Amplitude Converter module is compressed using Quarter Wave Symmetry technique and is entirely made up of combinational logic inserted into 12 Complementary Dual-Phase Latch-Based pipeline stages. The logic is represented in the form of Sum of Product (SoP) terms obtained from a 14×10 bits sinusoidal Look-Up-Table. The proposed DDFS is designed and simulated based on TSMC 65nm CMOS standard-cell technology. A maximum data sampling rate of 6.8 GS/s and 0.022 W/ GS/s Power Efficiency (PE) is expected.

In order to test the working state of adaptive optics system, it is necessary to design an online sweep-frequency circuit module to test the frequency response of the adaptive system. Sweep-frequency signal generator based on Direct Digital frequency Synthesis (DDS) is one of the core components. But the classic DDS technology also has some drawbacks: the truncation error of phase, the truncation error of magnitude (caused by memory FWL) and high occupancy of ROM. These are also the optimization directions in this paper. This paper presents a FPGA-based DDS sweep-frequency signal generator suitable in adaptive optics. It has a low occupancy rate with ROM. And in the case of low-ROM, the paper reduces the noise generated by the truncation error of phase and the truncation error of magnitude of DDS sweepfrequency signal generator by method of linear interpolation. The results show that, when the reference frequency is 100 MHz, the frequency resolution can be as low as 0.025 Hz. It only takes up 0.5 KB ROM with the ROM compression ratio of 64:1 in the optimized scheme in the paper and has higher precision due to the method of linear interpolation than the unoptimized scheme, which can meet the engineering needs. Compared with other schemes, the scheme in the paper improves signal accuracy in the case of reducing the truncation error of phase, the truncation error of magnitude and the occupancy rate with ROM, but only adds a multiplication and division circuit, which is a practical solution.

Phase to amplitude conversion is an essential part in the technique of direct digital frequency synthesis. A novel theory of phase to amplitude conversion named curve approximation is proposed in this paper to solve the existing problems of present digital frequency synthesizers. It has more advantages over traditional phase to amplitude conversion methods, such as simple hardware circuit, fast conversion speed, low loss and high precision. A mathematical function approximating normalized waveforms is presented in the paper and then is corrected by a small ROM lookup table containing the difference between normalized waveform and curve approximation. It can be seen from MATLAB simulation that the given curve is essentially coincident with the normalized waveform. Frequency synthesizer based on DSP and MCU verifies the feasibility of curve approximation in direct digital frequency synthesis. Experimental result shows that this method has excellent performance.

An efficient communication system requires synchronization between the transmitter and the receiver, which is achieved by generating the same local carrier frequency. Direct Digital Frequency Synthesizer (DDFS) is one of the methods to generate various frequencies, centered around a reference frequency. This paper presents the comparison between the DDFS implementation using the look-up table (LUT) method and the CORDIC, a multiplier-less algorithm. The implementation has been carried out in Simulink and various parameters have been analyzed.

In this paper, we propose an application of new direct digital frequency synthesizer, which clock frequency is up to 3.2 GHz. The design can generate single signal, chirp signal, stepped-frequency signal and stepped-frequency chirp signal from dc to 1500 MHz. The conclusions are drawn after comparing the NEW DDS with AD9858: phase noise and spurious spectrum of the NEW DDS are better than AD9858.