AD736外文翻译

FEATURES Computes True rms value Average rectified value Absolute value Provides 200 mV full-scale input range (larger inputs with input attenuator) High input impedance: 1012 Low input bias current: 25 pA maximum High accuracy: 0.3 mV 0.3% of reading RMS conversion with signal crest factors up to 5 Wide power supply range: +2.8 V, 3.2 V to 16.5V Low power: 200 mA maximum supply current Buffered voltage output No external trims needed for specified accuracy AD737an unbuffered voltage output version with chip power-down also availableGENERAL DESCRIPTION The AD736 is a low power, precision, monolithic true rms-to-dc converter. It is laser trimmed to provide a maximum error of 0.3 mV 0.3% of reading with sine wave inputs. Furthermore, it maintains high accuracy while measuring a wide range of input waveforms, including variable duty-cycle pulses and triac (phase)-controlled sine waves. The low cost and small size of this converter make it suitable for upgrading the performance of non-rms precision rectifiers in many applications. Compared to these circuits, the AD736 offers higher accuracy at an equal or lower cost. The AD736 can compute the rms value of both ac and dc input voltages. It can also be operated as an ac-coupled device by adding one external capacitor. In this mode, the AD736 can resolve input signal levels of 100 V rms or less, despite variations in temperature or supply voltage. High accuracy is also maintained for input waveforms with crest factors of 1 to 3. In addition, crest factors as high as 5 can be measured (introducing only 2.5% additional error) at the 200 mV full-scale input level. The AD736 has its own output buffer amplifier, thereby pro-viding a great deal of design flexibility. Requiring only 200 A of power supply current, the AD736 is optimized for use in portable multimeters and other battery-powered applications. The AD736 allows the choice of two signal input terminals: a high impedance FET input (1012 ) that directly interfaces with High-Z input attenuators and a low impedance input (8 k) that allows the measurement of 300 mV input levels while operating from the minimum power supply voltage of +2.8 V, 3.2 V. The two inputs can be used either single ended or differentially. The AD736 has a 1% reading error bandwidth that exceeds 10 kHz for the input amplitudes from 20 mV rms to 200 mV rms while consuming only 1 mW. The AD736 is available in four performance grades. The AD736J and AD736K grades are rated over the 0C to +70C and 20C to +85C commercial temperature ranges. The AD736A and AD736B grades are rated over the 40C to +85C industrial temperature range. The AD736 is available in three low cost, 8-lead packages: PDIP, SOIC, and CERDIP. PRODUCT HIGHLIGHTS 1. The AD736 is capable of computing the average rectified value, absolute value, or true rms value of various input signals. 2. Only one external component, an averaging capacitor, is required for the AD736 to perform true rms measurement. 3. The low power consumption of 1 mW makes the AD736 suitable for many battery-powered applications. 4. A high input impedance of 1012 eliminates the need for an external buffer when interfacing with input attenuators. 5. A low impedance input is available for those applications that require an input signal up to 300 mV rms operating from low power supply voltages. SPECIFICATIONS At 25C 5 V supplies, ac-coupled with 1 kHz sine wave input applied, unless otherwise noted. Specifications in bold are tested on all production units at final electrical test. Results from those tests are used to calculate outgoing quality levels.Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.THEORY OF OPERATIONAs shown by Figure 18, the AD736 has five functional subsections: the input amplifier, full-wave rectifier (FWR), rms core, output amplifier, and bias section. The FET input amplifier allows both a high impedance, buffered input (Pin 2) and a low impedance, wide dynamic range input (Pin 1). The high impedance input, with its low input bias current, is well suited for use with high impedance input attenuators. The output of the input amplifier drives a full-wave precision rectifier that, in turn, drives the rms core. The essential rms operations of squaring, averaging, and square rooting are performed in the core using an external averaging capacitor, CAV. Without CAV, the rectified input signal travels through the core unprocessed, as is done with the average responding connection (see Figure 19). A final subsection, an output amplifier, buffers the output from the core and allows optional low-pass filtering to be performed via the external capacitor, CF, which is connected across the feedback path of the amplifier. In the average responding connection, this is where all of the averaging is carried out. In the rms circuit, this additional filtering stage helps reduce any output ripple that was not removed by the averaging capacitor, CAV. TYPES OF AC MEASUREMENT The AD736 is capable of measuring ac signals by operating as either an average responding converter or a true rms-to-dc converter. As its name implies, an average responding converter computes the average absolute value of an ac (or ac and dc) voltage or current by full-wave rectifying and low-pass filtering the input signal; this approximates the average. The resulting output, a dc average level, is scaled by adding (or reducing) gain; this scale factor converts the dc average reading to an rms equivalent value for the waveform being measured. For example, the average absolute value of a sine wave voltage is 0.636 times VPEAK; the corresponding rms value is 0.707 VPEAK. Therefore, for sine wave voltages, the required scale factor is 1.11 (0.707/0.636). In contrast to measuring the average value, true rms measurement is a universal language among waveforms, allowing the magnitudes of all types of voltage (or current) waveforms to be compared to one another and to dc. RMS is a direct measure of the power or heating value of an ac voltage compared to that of a dc voltage; an ac signal of 1 V rms produces the same amount of heat in a resistor as a 1 V dc signal.Mathematically, the rms value of a voltage is defined (using a simplified equation) as This involves squaring the signal, taking the average, and then obtaining the square root. True rms converters are smart rectifiers; they provide an accurate rms reading regardless of the type of waveform being measured. However, average responding converters can exhibit very high errors when their input signals deviate from their precalibrated waveform; the magnitude of the error depends on the type of waveform being measured. For example, if an average responding converter is calibrated to measure the rms value of sine wave voltages and then is used to measure either symmetrical square waves or dc voltages, the converter has a computational error 11% (of reading) higher than the true rms value (see Table 4). CALCULATING SETTLING TIME USING FIGURE 16 Figure 16 can be used to closely approximate the time required for the AD736 to settle when its input level is reduced in amplitude. The net time required for the rms converter to settle is the difference between two times extracted from the graph (the initial time minus the final settling time). As an example, consider the following conditions: a 33 F averaging capacitor, a 100 mV initial rms input level, and a final (reduced) 1 mV input level. From Figure 16, the initial settling time (where the 100 mV line intersects the 33 F line) is approximately 80 ms.The settling time corresponding to the new or final input level of 1 mV is approximately 8 seconds. Therefore, the net time for the circuit to settle to its new value is 8 seconds minus 80 ms, which is 7.92 seconds. Note that because of the smooth decay characteristic inherent with a capacitor/diode combination, this is the total settling time to the final value (that is, not the settling time to 1%, 0.1%, and so on, of the final value). In addition, this graph provides the worst-case settling time because the AD736 settles very quickly with increasing input levels.RMS MEASUREMENTCHOOSING THE OPTIMUM VALUE FOR CAV Because the external averaging capacitor, CAV, holds the rectified input signal during rms computation, its value directly affects the accuracy of the rms measurement, especially at low frequencies. Furthermore, because the averaging capacitor appears across a diode in the rms core, the averaging time constant increases exponentially as the input signal is reduced. This means that as the input level decreases, errors due to nonideal averaging decrease, and the time required for the circuit to settle to the new rms level increases. Therefore, lower input levels allow the circuit to perform better (due to increased averaging) but increase the waiting time between measurements. Obviously, when selecting CAV, a trade-off between computational accuracy and settling time is required. RAPID SETTLING TIMES VIA THE AVERAGE RESPONDING CONNECTION Because the average responding connection shown in Figure 19 does not use the CAV averaging capacitor, its settling time does not vary with the input signal level. It is determined solely by the RC time constant of CF and the internal 8 k resistor in the output amplifiers feedback path.DC ERROR, OUTPUT RIPPLE, AND AVERAGING ERROR Figure 20 shows the typical output waveform of the AD736 with a sine wave input applied. As with all real-world devices, the ideal output of VOUT = VIN is never achieved exactly. Instead, the output contains both a dc and an ac error component. As shown in Figure 20, the dc error is the difference between the average of the output signal (when all the ripple in the output is removed by external filtering) and the ideal dc output. The dc error component is therefore set solely by the value of the averaging capacitor used. No amount of post filtering (that is, using a very large CF) allows the output voltage to equal its ideal value. The ac error component, an output ripple, can be easily removed by using a large enough post filtering capacitor, CF. In most cases, the combined magnitudes of both the dc and ac error components need to be considered when selecting appropriate values for Capacitor CAV and Capacitor CF. This combined error, representing the maximum uncertainty of the measurement, is termed the averaging error and is equal to the peak value of the output ripple plus the dc error.As the input frequency increases, both error components decrease rapidly; if the input frequency doubles, the dc error and ripple reduce to one quarter and one half of their original values, respectively, and rapidly become insignificant.AC MEASUREMENT ACCURACY AND CREST FACTOR The crest factor of the input waveform is often overlooked when determining the accuracy of an ac measurement. Crest factor is defined as the ratio of the peak signal amplitude to the rms amplitude (crest factor = VPEAK/V rms). Many common waveforms, such as sine and triangle waves, have relatively low crest factors (2). Other waveforms, such as low duty-cycle pulse trains and SCR waveforms, have high crest factors. These types of waveforms require a long averaging time constant (to average out the long periods between pulses). Figure 8 shows the additional error vs. the crest factor of the AD736 for various values of CAV.APPLICATIONS CONNECTING THE INPUT The inputs of the AD736 resemble an op amp, with noninverting and inverting inputs. The input stages are JFETs accessible at Pin 1 and Pin 2. Designated as the high impedance input, Pin 2 is connected directly to a JFET gate. Pin 1 is the low impedance input because of the scaling resistor connected to the gate of the second JFET. This gate-resistor junction is not externally accessible and is servo-ed to the voltage level of the gate of the first JFET, as in a classic feedback circuit. This action results in the typical 8 k input impedance referred to ground or reference level. This input structure provides four input configurations as shown in Figure 21, Figure 22, Figure 23, and Figure 24. Figure 21 and Figure 22 show the high impedance configurations, and Figure 23 and Figure 24 show the low impedance connections used to extend the input voltage range. 中文翻译运算真有效值RMS平均整流值绝对值提供满量程200mV范畴内输入电压(较大输入的输入衰减器)高输入阻抗:1012低的输入偏置电流:25 pA最大值精度高:0.3 mV0.3%的读入波顶因数的有效值转换提高到5宽供电范畴:+ 2.8V,3.2V到16.5 V低功率:最大200mA就可正常运营缓冲输出电压没有外部合同需要规定精确性AD737-是一种芯片断电也可使用的非缓冲电压输出的版本总体描述AD736是一种低功率、精密、真有效值单块集成电路的直流转换器。它是通过激光修正提供一种最大误差0.3 mV0.3%的读如与正弦波的输入。此外,它在很宽的范畴内测量输入波形仍能保证高精度，输入波形,涉及脉冲占空比可变和相控正弦波。这个芯片低成本、体积小使它很以便在非有效值精密整流器在许多应用里有了很大的提高。比较这些芯片, AD736能提供更高的精确度以相似或更低的成本。AD736可以计算交流电和直流电两种输入电压的有效值。它也可以添加一种外部电容器作为一种交流耦合的操作设备。在这种状况下, AD736可以解决输入信号有效值等于或少于100uV,虽然温度和电压变化。高精度也保证输入的波形在1到3的峰值因子。此外,高达5波顶因数可以测量(引起附加的误差仅为2.5%)满量程200mV的水平。AD736有它自己的输出缓冲放大器,从而大大提高设计的灵活性。只需要200A供电电流, AD736使便携式万用表和其她电池驱动的应用得到优化。AD736容许两个信号输入端子可以选择:一种高阻抗场效应管输入(1012)直接接口与高Z输入衰减器和低阻抗输入(8 k),这样可以容许测量300mV输入值从最低的电源电压+ 2.8 V,3.2 V。两个输入可以是使用单端或双端。AD736有1%的错误读入带宽，超过10KHZ的输入振幅从20 mV有效值到200mV 有效值然而只消耗1 mW。AD736有四个性能级别AD736J和AD736K的额定级别是在0到+ 70C 、 20C到85C商业级温度范畴。AD736A和AD736B的额定级别在40到85C 工业级温度范畴。这个AD736是可运用的在三种低成本、8脚:PDIP,SOIC,CERDIP封装。产品亮点1.AD736可以计算平均矫正值、绝对值、真有效值等多种输入信号。2. AD736只需一种外部组件,一种平均电容、就可以进行真有效值的测量。3.低功耗1 mW使AD736适合许多电池驱动的应用。4.一种高阻抗1012的输入，当输入与衰减器连接时不需要外部的缓冲。5.一种低阻抗的输入可供那些需要一种输入信号达到300 mV有效值在低电压下运营的应用。规格 使用温度25C5 V、交流耦合 1KHZ正弦波输入,除非另有注明。阐明书是在大胆的测试所有的产品单元后完毕的。这些测试成果用于计算出厂质量。超过最大额定值也许对设备导致永久性的损坏。这是额定值仅供参照,在高于额定值或其她的环境下设备的功能正常运营是不可取的。在最大额定值下使用,也许影响器件的可靠性。工作原理如图18所示，AD736有五个功能分段:输入放大器,全波整流器(FWR)、有效值的核心、输出放大器、偏压部分。若场效应管输入放大器都容许的高阻抗,缓冲输入(Pin 2)和一种低阻抗、宽动态范畴输入(Pin 1)。高阻抗输入,以其低的输入偏置电流,很适合使用高阻抗输入衰减器。输入放大器的输出驱动全波精密整流器,进而带动有效值核心。基本的有效值操作就是平方,平均值,开平方在内部核心运营，使用一种外部平均电容器，CAV。没有CAV ,整流后的输入信号穿越核心未被解决,由于已经完毕平均响应连接 (参见图19)。最后一节、输出放大器、缓冲器输出从核心容许可选择低通滤波通过外部电容器、CF连接通过反馈放大器。在平均响应的联系,在这里所有的平均值运算被执行。在有效值电路中,该附加滤波阶段有助于减少输出信号中没有被平均电容过滤掉的脉动。交流测量的类型AD736可以测量交流信号通过操作要么是平均响应整流器或一种真有效值的直流转换器。正如其名字所示,一种平均响应整流器计算交流电压得平均绝对值(或交流和直流)或者目前的全波整流或低通滤波输入信号，这个接近平均值。输出成果,一种直流平均级别,按增长(或减少)增益来平衡;这种平衡因素转换的直流平均读入到一种真有效值等价于波形的测量。例如,一种正弦波电压的平均绝对值是VPEAK 0.636倍,相应的有效值是0.707VPEAK。因此,对于正弦波电压,所需的平衡因素是1.11(0.707/0.636)。与测量平均值形成对比,真有效值的波形测量是一种世界通用方式,容许选择所有类型的电压(或电流)波形被比作一种到另一种和到直流。有效值就是在相似的电阻上分别通以直流电流和交流电流，通过一种交流周期的时间，它们在电阻上所损失的电能相等。1V的交流与1V的直流在同一电阻上产生相似的热量。数学的均方根值电压值的定义(使用一种简化方程)这涉及把信号平方,做平均值,然后在做平方根的计算。真有效值的转换器是机灵的整流器;她们提供一种精确的真有效值读取无论是哪类波形的测量。然而,平均响应转换器当她们的输入信号偏离事先标定的波形会浮现误差;产生误差的大小取决于波形的被测形式。例如,如果一种平均响应转换器被校准去测量正弦波电压,然后又用于测量对称方波和直流电压，转换器就会产生(读入)高于真有效值11%的计算误差(见表4)。计算稳定期间使用图16图16可以用来得到粗略的估计AD736解决输入电平振幅下降所需的时间。真有效值转换器来解决两次提取图形之间的差别所需的净时间 (初始时间减去最后稳定期间)。例如,考虑如下条件: 一种33F平均电容器,一种初始有效值为100mV的输入电平,和一种最后(减少)1 mV输入电平。从图16,初步建立时间(这里的100mV的线与33F的线相交)大概是80毫秒。相应的达到新的或最后输入的1 mV电平所需的稳定期间约为8秒。因此,电路来解决新值的净时间是8秒减80毫秒,即7.92秒。注意到电容器/二极管组合所固有的衰减平滑特性,这是总稳定期间到最后值(即不是稳定期间到1%,0.1%,等等,最后值)。此外,本图提供了最坏状况的稳定期间，是由于AD736解决递增的输入电平非常迅速。CAV有效值(RMS)测量的最佳选择由于外部平均值电容器CAV,在有效值计算时保存整流输入信号 ,其值直接影响有效值的测量精度,特别对于低频来说。此外,由于平均电容器在有效值核心穿过一种二极管。当输入信号减小时，平均时间常数以指数形式增长。这意味着只要输入电压减少,误差由于非抱负的平均而值减小 ,而电路所需解决新的有效值电压的时间增长了。因此,低输入电平使电路工作的更好(由于平均值增长),增长了测量操作时的等待时间。很明显,当选择了CAV,精确计算与需要达到的稳定期间是一种平衡关系。通过的平均响应连接的迅速建立时间由于在图19展示出的平均响应关系没有使用CAV平均电容器,其稳定期间不随输入信号电平变化。它仅由RC时间常数的CF和内部8 k电阻在输出放大器的反馈途径上而决定。直流误差、输出的波纹,和平均误差图20显示了典型的AD736正弦输入的输出波形应用。所有都是真实的设备,抱负的输出VOUT = VIN是永远不能达到这样的。相反,输出既具有直流输和交流误差的构成部分。如图20时,直流误差是区别于平均输出信号(当所有的输出脉动都被外部滤波掉了)和抱负的直流输出。直流误差的构成仅仅是平均值由于电容的使用。虽然再多的后置滤波(也就是用一种非常大的CF)容许输出电压等于抱负值。交流误差构成,一种输出脉动,可以被很容易被消除通过使用一种足够大的滤波电容器、CF。在大多数状况下,直流和交流误差的成分需要被考虑当选择合适的电容器CAV和电容器CF的值时。这综合误差,代表着最大的不拟定度量,是所谓的平均误差它等于输出脉动的峰值加上直流误差。当输入频率的升高,两者误差部分迅速减少;如果输入频率加倍,直流误差和脉动减小到四分之一和原始值的一半，迅速成为无关紧要的因素。交流测量精度和振幅因数当决定一种交流测量的精确度输入波形的振幅因数常常被忽视。振幅因数被定义为最大信号振幅与有效值振幅之比 (振幅因数= VPEAK / V rms)。许多常用的波形,如正弦波和三角波,有相对较低的振幅因数(2)。其她波形,如低频宽比脉冲序列和可控硅波形,具有高振幅因数。这些类型的波形需要很长的平均时间常数(在脉冲之间需要很长的周期达到最后的平衡)。图8显示附加的误差对比，对于多种各样的CAV值的AD736振幅因数。应用输入的连接AD736的输入类似一种带着同向和反向的运算放大器。输入级是结型场效应管(JFET)可以由1脚和2脚输入。指定为高阻抗输入、脚2直接连接到结型场效应管（JFET）门。脚1是低阻抗输入由于缩放电阻连接到第二个结型场效应管(JFET)门。门电阻没有在外部连接,是不容易servo-ed外部的电压水平的门,第一JFET,像一种典型的反馈电路。这个功能导致典型的8 k输入阻抗波及到地或参照电平。该输入装置提供了四个输入配备如图21,图22,图23,图24。图21图22展示高阻抗配备,图23和图24展示低阻抗关系用于扩展输入电压范畴。