A look-up-table digital predistortion technique for high-voltage power amplifiers in ultrasonic applications

In this paper, we present a digital predistortion technique to improve the linearity and power efficiency of a high-voltage class-AB power amplifier (PA) for ultrasound transmitters. The system is composed of a digital-to-analog converter (DAC), an analog-to-digital converter (ADC), and a field-programmable gate array (FPGA) in which the digital predistortion (DPD) algorithm is implemented. The DPD algorithm updates the error, which is the difference between the ideal signal and the attenuated distorted output signal, in the look-up table (LUT) memory during each cycle of a sinusoidal signal using the least-mean-square (LMS) algorithm. On the next signal cycle, the error data are used to equalize the signal with negative harmonic components to cancel the amplifier's nonlinear response. The algorithm also includes a linear interpolation method applied to the windowed sinusoidal signals for the B-mode and Doppler modes. The measurement test bench uses an arbitrary function generator as the DAC to generate the input signal, an oscilloscope as the ADC to capture the output waveform, and software to implement the DPD algorithm. The measurement results show that the proposed system is able to reduce the second-order harmonic distortion (HD2) by 20 dB and the third-order harmonic distortion (HD3) by 14.5 dB, while at the same time improving the power efficiency by 18%.     

Chirp信号发生器的设计与实现

本文利用DDS技术在FPGA平台上设计实现了一种Chirp信号发生器,该信号发生器能产生标准的Chirp波形和正余弦波形,通过PC机软件可调整波形的类型、频率和相位。该信号发生器输出频率范围为0．01Hz-25MHz,频率分辨率为0．01Hz,具有控制灵活,输出稳定的优点。     

捷变正弦信号源波形建立时间的精确测量

针对正弦信号源捷变状态切换后的建立时间、开机后波形建立时间以及过载恢复时间等的精确测量问题,提出了一种基于局域波形四参数拟合的测量分析方法,然后将拟合模型参数拓展到全局,进而获得拟合回归波形与过渡过程波形的回归残差波形。该波形的收敛过程反映了正弦波建立过程中的残差收敛变化过程。以它为目标对象,加上主观设定的建立时间的条件判据,可以获得正弦建立时间的起始和终止两个时刻点,最终获得完整的正弦信号建立时间。在两组不同条件下的状态切换实验结果,验证了该方法的有效性和可行性。该方法也可以推广应用到脉冲调频、脉冲调幅、脉冲调相、捷变频信号的建立时间测量评价中。     

A multiphase direct-digital-synthesis sinewave generator forhigh-accuracy impedance comparison

In this paper we report on the realization and characterization of a multiphase sinewave generator based on the direct-digital-synthesis technique using the latest Analog Devices direct-digital-synthesizer model AD9853. The generator is intended for use in high-accuracy impedance intercomparison setups; thus, particular attention is paid to the stability and distortion of the sine wave output signal. The sinewave frequency can be tuned in the range from 16 Hz to 16 kHz with a resolution <10 μHz and with a relative frequency short-term stability of 10^-7, whereas the sinewave long-term amplitude stability is better than 10^-6 at full amplitude output. Signal amplitude, frequency, and phase are monitored and set by means of a personal computer     

Josephson-Voltage-Standard-Locked Sine Wave Synthesizer: Margin Evaluation and Stability

This paper describes a Josephson-voltage-standard-locked synthesizer where a commercial digital-to-analog converter is used as a sine wave generator. The output amplitude of the generator is controlled by the calculable fundamental of the stepwise waveform generated by a SINIS Josephson junction array. Such a system combines the versatility of a commercial source with the stability and accuracy of the Josephson standard. By discarding the measurements performed during the transients, broad voltage steps of 1.7 mA were obtained up to frequencies of 500 Hz.      

光纤水听器调制激光光源的一种实现方法

在干涉型光纤水听器的信号检测技术中,采用相位载波零差检测方式,直接调制激光光源,具有明显的优越性。提出了一种实现方法,通过产生高频正弦波,对激光光源(多量子阱分布反馈激光器),进行直接驱动调制。光源调制输出波形精确多样(正弦波、三角波(包括锯齿波)和方波),输出频率大范围(0～20MHz),连续可调。实验表明达到了水听器对光源的要求。此调制技术也可在光纤通信等其它领域得以应用。     

Digital spectra of nonuniformly sampled signals. II. Digitallook-up tunable sinusoidal oscillators

For Part I see ibid., vol.37, no.2, June 1988. The author presents theories and applications of a digital spectrum analysis technique for a class of nonuniformly sampled signals. The structure of the harmonic components present in a digitally synthesized sine wave is analyzed using a table look-up method. The digital table look-up method offers several desirable features, such as high-frequency stability and precision control of both the frequency and the phase of the generated sine wave. However, undesirable spurious harmonic components are generated when one tries to tune to different frequencies by manipulating the memory-addressing mechanism rather than loading a new waveform sample into the waveform memory, which is generally time-consuming and sometimes infeasible. The frequencies, amplitudes, and phrases of all the spurious harmonic components are derived in closed form     

正弦声信号在钻柱中传播的有限差分法模拟

将钻柱简化为理想周期性管结构,利用有限差分方法,对不同频率的正弦声信号在周期性管结构中传输过程中,存在透射系数及衰减系数差异较大的现象进行数值模拟与分析,得到不同频率的正弦声信号穿过周期性管结构后信号的时域及频域分布。分别对400 Hz和500 Hz的正弦声信号在周期性管结构中传输进行了模拟。模拟结果表明：处于带通频率的正弦声信号在周期性管结构中传播波形失真小,频谱变化小,传播性能良好;带阻频率的正弦声信号在周期性管结构中传播波形失真严重,频谱变化很大,几乎不能通过。模拟结果与同类研究成果有较好的一致性。验证该模型和所采用的数值方法的有效性,为钻柱中声信号传输的数值模拟及与其类似的实际问题的数值模拟提供参考。     

基于DSP的航空测试交流电源

介绍了一种基于DSP的航空测试交流电源.该交流电源不仅能够输出飞机交流用电设备在不同工作状况下的频率幅值可调的正弦电压,而且能够输出周期性畸变电压.该电源采用数模混合控制及重复控制方法,数字部分实现高精度的波形发生器和电压有效值控制;模拟部分采用电压电流瞬时值控制,提高响应速度.最后给出测试波形.     

Digital Walsh-Fourier Analysis of Periodic Waveforms

A digital process is described for obtaining the Walsh-Fourier series of a periodic waveform, which requires at most two cycles of the waveform under measurement. The first cycle of the periodic waveform is required for the determination of period. The coefficients of the Walsh-Fourier series are obtained during the second cycle only, and they are available at the end of the cycle. Given the Walsh-Fourier coefficients of the periodic wave, the individual sine and cosine components of its Fourier series may be obtained using conversion formulas. Special features of the process are that there are no theoretical low-frequency limitations, and for an instrument with an internal clock whose frequency lies in the range 1 Hz to 1 MHz, the fundamental frequency component of a signal that can be analyzed would be in the range 1 cycle in 11.6 days to 60 Hz. Also, whereas the digital processes required to obtain a Fourier series directly are complicated by the need to multiply sample values of voltage by sines and cosines, which are themselves functions of time, determination of Walsh-Fourier coefficients is achieved very simply by using gating circuits. Generation of the required Walsh functions for a periodic signal of any fundamental frequency within the design range has been achieved.     

Synthesising gene clock with toggle switch and oscillator

The usefulness of a genetic clock lies in its role to stimulate a sequence of logic reactions for sequential biological circuits. A clock signal is a periodic square wave, its amplitude alternates at a steady frequency between fixed minimal and maximal levels. Transition between the minimum and the maximum is instantaneous for an ideal square wave; however, the function is unrealisable in physical bio‐systems. This research develops a new genetic clock generator based on a genetic oscillator, in which, a sine wave generator is adopted as a signal oscillator. It is shown that combination of a genetic oscillator with a toggle switch is able to generate clock signals forming an efficient way to generate a near square wave. In silico study confirms the proposed idea.Inspec keywords: genetics, oscillators, biological techniques, square‐wave generators, switchesOther keywords: toggle switch, genetic clock, logic reaction sequence, sequential biological circuits, clock signal, periodic square wave, physical biosystem, genetic clock generator, sine wave generator, signal oscillator, genetic oscillator     

Limitation of the frequency stability by local oscillator phase noise: new investigations and natural improvements

In frequency standards in which the atoms have a continuous interaction with the probe signal, local oscillator phase noise may limit medium term frequency stability. This spurious effect cannot be suppressed whenever there Is any truncation in the spectrum of the resonator response. Nevertheless, a simultaneous processing of the probe signal, similar to that of the NIST, and of the resonator response (by means of an appropriate demodulation) makes it possible to reduce this limiting effect. Previously achieved with a square wave frequency modulation, this result is now extended to various frequency modulations. An uncontrolled distortion in the demodulation waveform may significantly degrade the performance. For the case of a square wave phase modulation, the limiting effect also exists, but it is smaller than for a frequency modulation. When the phase noise of the local oscillator is naturally "not flat", it is possible to easily reduce the spurious effect: using the quasi-static approximation, one can calculate various optimized demodulation waveforms and the corresponding improvements. For the simplest optimized demodulation (f (M), 3f(M)), theoretical predictions are experimentally confirmed for flicker phase noise and flicker frequency noise.     

Spectrally pure excitation signals: only a dream?

For accurate testing of a nonlinear device-under-test (DUT), the spectral purity of the input signal is utterly important. This paper describes a method to create very pure signals, such as sine waves, dual-tones, or multitones, using only power measurements. The signals are generated with an arbitrary waveform generator. Any unwanted spectral line is removed, independent of its exact origin. This allows to apply the correct signal to the DUT, even if the signal source is not perfect or is followed by filters or amplifiers with a small nonlinear distortion. Measurements are used to demonstrate the capabilities of the method.     

The use of DFT windows in signal-to-noise ratio and harmonicdistortion computations

The discrete Fourier transform (DFT) can be used to compute the signal-to-noise ratio (SNR) and harmonic distortion of a waveform recorder. When the data record contains a non-integer number of cycles of the sine wave, energy leaks from the sine wave and its harmonics to adjacent frequencies. A.L. Benetazzo et al. (1992) describe a windowed DFT method for computing the RMS value of a sine wave from the magnitude of the main lobe of its DFT and recommend the use of minimum energy windows. We present criteria for choosing the DFT window. A constraint for the window coefficients is derived to insure that quantization error does not influence the estimate of the amplitude of a sine wave from the main lobe of its DFT     

A New Low Cost Linear Resolver Converter

A new low cost converter topology is proposed for sinusoidal position encoders. The converter enables determination of the angle from the sine and cosine signals of the encoder. When used with resolvers, the implementation of the present scheme takes advantage of the available excitation signal used to operate the device. This trigonometric reference signal is optimally used to generate an analogue signal equivalent to a digital look-up table (LUT). This enables determination of the mechanical angle without using LUT, A/D, and D/A converters. The scheme is optimized in order to achieve highest possible precision. Beside simplicity of its implementation, the proposed converter offers the advantage of robustness to amplitude fluctuation of the transducer excitation signal. The converter was implemented using ordinary low-cost analog components. The theory of operation, computer simulation, and experimental results are given.      

基于傅里叶变换的正弦信号源波形失真评价方法

介绍了一种直接利用经典傅里叶变换技术评价正弦信号源波形总失真度的过程和方法。借助于周期的精确测量技术,实现基波参数的精确测量。用时域能量方式计算失真,其内涵全面,包括了谐波、杂波、噪声等全部影响,并对测量系统本身的影响进行了补偿。同时,对不同条件下的失真度测量误差进行了分析,用一组仿真数据的实验结果,验证了正确性及可行性。所述方法可用于正弦信号波形失真度的精确测量和计量校准,尤其适用于大失真度的测量。     

全数字PGC解调的载波相位超前技术

分析相位载波(PGC)解调中载波相位延迟产生的影响,表明载波相位延迟引起解调输出幅值衰减,严重时导致解调输出恒为零.提出采用载波相位超前技术消除其不利影响.在全数字PGC 解调系统中,采用余弦查找表(LUT)方式生成载波数字波形,通过在LUT 的地址输入端引入固定偏置,生成相位超前的载波,补偿解调系统中固有的延迟,达到消除不利影响的目的.固定偏置可以通过对解调系统进行分析和测试获得.实验结果表明,载波相位超前技术是有效的.     

Optical-fiber finger photo-plethysmograph using digital techniques

This paper presents digital techniques to design an optical-fiber photo-plethysmograph. This noninvasive method is based on the measurement of the intensity of an infrared-light beam, which penetrates the index finger. Sinusoidal modulation of the light-beam by driving an infrared LED is proposed. The method of direct digital synthesis is used to produce a very stable sinusoidal waveform. Optical fibers are used to transfer the light to and from the sampling point. Synchronous amplitude demodulation is used here instead of using analog low-pass filters, so the information concerning the amplitude is almost noiseless. Off-line frequency analysis of the peripheral volume pulse-wave signal is performed. The power content in the harmonics of this pulse wave may be a useful measure of aging and vascular disease     

一种基于残周期正弦波拟合的相位差测量方法

针对不足一个波形周期的相位差测量,提出使用残周期正弦波拟合算法实现的技术方法,给出了原理和实现过程。针对该条件下相位差的测量不确定度,给出了使用波形局域失真和噪声信号比方式,以实际估计参数条件下的仿真计算进行评估的模式。最后,使用激光测振仪校准中的三个相位之间的相位差进行了实验验证,结果表明,在约0.5个周期条件下获得的相位差与多周期条件下的相位差仅仅相差1°左右,证明了该方法的有效性和可行性,为正弦相位差测量提供了一种新的实现方式。     

基于增量式光电编码器细分的自适应滤波技术研究

利用光栅副调制原理,在建立了光栅副调制几何光学模型与物理光学模型的基础上,提出了一种针对增量式编码器细分的自适应滤波方法。分析莫尔条纹光电信号输出波形不确定的原因,通过自适应滤波方法将高频信号滤除保留基频信号。自适应滤波效果等价于一个中心频率为基频的窄带带通滤波器,当基频随机变化时其通带也会随之改变。实验证明采用这种自适应滤波技术可以较好地滤除计数信号中除基频外所有高频分量,使莫尔条纹光电信号输出波形趋近于标准正弦波,将信号失真量减小了约7/8。