数字音频D类功放电源误差校正方法研究

为了实时校正供电电源噪声引起的数字音频D类功放输出误差,提出一种基于FPGA的电源误差校正方法。使用高精度ADC芯片将电源纹波信号转化为数字量后送入FPGA,校正模块根据电源纹波的大小对数字音频D类功放Sigma-Delta调制器输入值进行预校正处理,从而实现在功放输出端有效的抑制电源噪声。经过实际电路测试,该方法可以有效的抑制电源噪声对数字音频D类功放的影响,电源抑制比达到36.78 dB。     

Effect of dead time on closed-loop regulation

The steady-state performance of closed-loop regulation in the presence of random disturbance is found to be dependent on a crosspower term. Without dead time, this term is negative, resulting in good disturbance rejection. The presence of dead time will increase the crosspower term and may even reverse its sign, resulting in poorer performance. Furthermore, the closed-loop regulation may be worse than the open-loop, and a decrease in the controller gain may be needed to improve disturbance rejection.     

Detection of nonlinear distortion in audio signals

Nonlinear distortion of a signal passing through a system may be caused by a number of factors. One of those factors, a limiter like transfer function, is considered. The nonlinear distortion causes a change in the probability density function (PDF) of the signal. The PDF of the signal can be characterized by the coefficients of a fifth-order polynomial fitted to the PDF curve. The coefficients are used as a vector input to an artificial neural network trained to classify the vector as belonging to a distorted or undistorted audio signal. Results show that the artificial neural network is able to classify signals, with PDFs indicating the presence of significant high amplitude components, into distorted or undistorted. A low amplitude signal will not be distorted during its passage through a nonlinear system and therefore the output will be classified as "not distorted". This gives rise to, what seem to be, errors in the classification of signals. However, the technique developed identifies distortion in the signal and not in the system through which the signal has passed.     

低失真MnZn铁氧体中ZnO含量对磁特性的影响

为了提高非对称数字用户线(ADSL)接入系统的网络传输质量,采用传统氧化物陶瓷工艺制备了低失真MnZn铁氧体,并研究了在Fe2O3含量不变的前提下,ZnO含量与其磁特性的关系。结果表明:适量的ZnO可以提高起始磁导率μi,降低磁滞常数ηB。随着ZnO含量的增加,μi值先增大后减少,截止频率fr先减少后增加。当x(ZnO)为23%时,其μi=8 100,ηB=0.42×10–6/mT。     

Measurement of harmonic distortion in microwave photodetectors

The use of an offset phase-lock heterodyne system with a large dynamic range (>110 dB) for measuring photodetector (PD) harmonic distortion out to microwave frequencies is discussed. Up to 40 harmonics and second-harmonic levels only 17.8 dB below the fundamental were observed in high-speed PDs with only 1.7 mW incident. Measurements of harmonic power versus incident optical power are reported, along with associated PD bandwidth reduction     

Intermodulation and harmonic distortion in InGaAsP lasers

A theoretical and experimental study is presented of intermodulation and harmonic distortion in high-speed 1.3 and 1.5 ?m InGaAsP lasers modulated at frequencies up to 8 GHz. It is found that all lasers measured, including Fabry-Perot and distributed feedback lasers, generate approximately the same distortion levels for a given modulation depth and relaxation resonance frequency. There are minor differences between lasers, which result from differences in the damping of the small-signal resonance peak.     

Automatic topology selection and sizing of class-D loop-filters for minimizing distortion based on an evolutionary optimization kernel

This paper presents an optimization methodology for continuous time loop-filters design applied to Class-D amplifiers. The methodology is based on an evolutionary optimization approach which integrates both the topology selection and circuit sizing by automatically generating optimal sized topologies and performance tradeoffs for the Class-D amplifier. The presented approach is demonstrated on two cases: for the design of a half-bridge amplifier and for a fully differential BTL class-D loop filter topology that achieves less than 0.003% THD at 680?mW output power in typical 0.18???m CMOS technology.     

Generation of harmonic distortion at fibre connectors

Harmonic distortion generated by the Fabry-Perot resonator at fibre connectors is described. The maximum second-harmonic distortion is calculated as a function of end separation for GaAlAs lasers. A ?42 dB second-harmonic distortion is generated in 100 ?m end separation, which is harmful in analogue transmission systems.     

Theory of harmonic distortion at fibre connectors

A simple empirical model is proposed for the intensity transmissivity of the Fabry-Perot resonator. Using this model closed-form expressions are derived for the harmonic-distortion generated at fibre connectors.     

Second- and third-order harmonic distortion in DFB lasers

The second- and third-order harmonic distortion in distributed feedback (DFB) lasers is simulated using a time domain large signal dynamic model. The effects of the longitudinal spatial hole burning, nonlinear gain, spontaneous emission, and current leakage are included in the model. Composite second-order (CSO) and composite triple beat (CTB) are calculated for an 80 channel 60-540 MHz system with 3% modulation depth in each channel. The simulation results are compared with the experimental harmonic distortion measurements     

Frequency dependent harmonic distortion in a multiple-quantum-wellelectroabsorption modulator

The frequency dependence of the harmonic distortion in a multiple quantum-well electroabsorption waveguide modulator is demonstrated for the first time. Low-frequency measurements agree with calculation of the harmonic distortion based upon the static nonlinear relationship between the intensity and the applied voltage. However, observed harmonic distortion at RF frequencies is significantly larger than the observed harmonic distortion due to low-frequency modulation. The frequency dependence of the harmonic indicates that a mechanism other than the nonlinear intensity-voltage relationship dominates at high frequency     

Analysis of harmonic distortion in single-channel MOS integrated circuits

Presents a general analysis for the calculation of harmonic distortion in single-channel monolithic analog MOS integrated circuits. Power series expressions are obtained for basic stages often used in an analog MOS technology. These include the depletion load inverter, enhancement load inverter, depletion load source follower, enhancement load source follower, and the differential pair. From the power series expressions, the second-order harmonic distortion is calculated. These results are compared with data obtained from a test chip.     

Temperature dependence of storage time in silicon p+-n-n+ switching diodes and reduction of harmonic distortion

Using the reverse-recovery technique, storage times in p+-n-n+ diodes have been measured as a function of temperature. In all cases the effective lifetime for injected charge increases with increasing temperature within the interval 0 to 180°C. This result was found to reduce second-harmonic distortion in p+-n-n+ switches by as much as 6 dB at 2.5 MHz.     

Effect of gain control and modulation on harmonic nonlinear operators, with application to audio signal processing

Results are given concerning multiplication and gain control of harmonic operators, especially in the zeroth harmonic case. Various types of signal multiplication are considered, including analytic signal multiplication. These results facilitate the design of low-distortion signal processors, since many measurements of signal statistics used a control signals, e.g. correlations, are ideally zeroth harmonic.     

On the harmonic distortion coefficients of active-loaded amplifiers

Starting from the modified Ebers-Moll model which represents the Early effect more accurately than conventional models with the Early voltage, new expressions to calculate the harmonic distortion coefficients of active-loaded BJT amplifiers are derived and applied to the determination of the optimum operating point, where the total harmonic distortion is at a minimum. The results are not obtainable with SPICE, therefore derived expressions provide the possibility of completing the simulation with manual calculations.     

A 20-W stereo class-D audio output power stage in 0.6-/spl mu/m BCDMOS technology

This paper presents a highly power efficient 2/spl times/20-W class-D audio output power stage implemented in 0.6-/spl mu/m BCDMOS technology. The presented power stage is capable of driving 2/spl times/8-/spl Omega/ loads from a 20-V power supply at a power efficiency approaching 90%. Circuit details of thermal detection, over-current protection, and startup speaker click/pop are also presented. The performance of open-loop Class-D output stages are limited by the distortion mechanisms present within the power stage itself. A third-order PWM modulator was prototyped and used to dramatically improve the performance of the Class-D output stage by using feedback. The results of this work are also presented.     

Effect of dead space on the excess noise factor and time responseof avalanche photodiodes

The effect of dead space on the statistics of the gain process in continuous-multiplication avalanche photodiodes (APDs) is determined using the theory of age-dependent branching processes. The dead space is the minimum distance that a newly generated carrier must travel in order to acquire sufficient energy to cause an impact ionization. Analytical expressions are derived for the mean gain, the excess noise factor, and the mean and standard deviation of the impulse response function, for the dead-space-modified avalanche photodiode (DAPD), under conditions of single carrier multiplication. The results differ considerably from the well-known formulas derived by R.J. McIntyre and S.D. Personick in the absence of dead space. Relatively simple asymptotic expressions for the mean gain and excess noise factor are obtained for devices with long multiplication regions. In terms of the signal-to-noise ratio (SNR) of an optical receiver in the presence of circuit noise, it is established that there is a salutory effect of using a properly designed DAPD in place of a conventional APD. The relative merits of using DAPD versus a multilayer (superlattice) avalanche photodiode (SAPD) are examined in the context of receiver SNR; the best choice turns out to depend on which device parameters are used for the comparison     

Adaptive nondisruptive measurement of harmonic distortion forvoiceband data transmission

Volterra functional expansions are power series with memory that explicitly characterize the input/output relationship of a finite-memory single-valued nonlinear black box whenever the latter is time-invariant and stable. The purpose of this paper is to introduce and report on the strengths and weaknesses of two distinct Volterra-series-type classes of adaptive nonlinear techniques for the quantitative measurement of second- and third-order harmonic distortion present in the communications channel of a, possibly signal space coded, QAM data communication system. Our investigation was originated as part of a request for new nondisruptive impairment measurement algorithms that would reliably characterize in real-time the performance of voiceband modems over both D1 conditioned private lines and the direct-distance-dialing (DDD) public switched network. Though, contrary to earlier studies, we do not contemplate nonlinear distortion compensator design, experimental evidence obtained by implementing the simplest of our nondisruptive algorithms on a digital signal processor chip verifies that over a certain range of signal-to-second- and third-order intermodulation distortion ratios our measurements are consistent with those obtained via the disruptive digital four tone test under a variety of voiceband telephone channel impairment conditions. Unfortunately, our experiments also indicate that neither the digital four-tone test nor any of our nondisruptive techniques have chances to prove useful for greater than 5% of the existing voiceband channels. However, this is entirely due to the special nature of the telephone channel environment and is not likely to dilute the importance of our proposal for other types of nonlinear environments such as radio channels or satellite links     

Integral function method for determination of nonlinear harmonic distortion

The analysis of harmonic distortion is of prime importance for the analog and mixed integrated circuits. Recently we presented a new integral function method (IFM), based on a completely new principle, which allows the calculation of harmonic distortion using the DC output characteristic of devices or circuits. In this work we complement the integral function method to provide direct calculation of the following distortion figures: total harmonic distortion (THD), second harmonic distortion (HD2) and third harmonic distortion (HD3), voltage intercept points (VIP) and the intermodulation distortion (IMD). The comparison with the same distortion figures calculated by the Fourier coefficients (FC), by direct AC measurements and from FFT in simulators, indicates that results obtained by IFM give an excellent agreement in the full range of the analyzed active regions. The IFM combines simplicity and computer efficiency with accuracy and with the possibility to easily analyze the distortion when varying any of the circuit or device parameters.