《恒流源在高精度数字多用表中的设计与实现外文翻译》由会员分享，可在线阅读，更多相关《恒流源在高精度数字多用表中的设计与实现外文翻译（6页珍藏版）》请在金锄头文库上搜索。
1、附录1 英文参考资料The constant current source in high precision digital design and implementation of multiple tables The constant current source in instrumentation, electronic equipment and high-tech science and technology is an important component of. In high precision digital multimeter, has the basic fun
2、ction of the resistance measurement, and the method of resistance measurement is usually through a resistance voltage (R-U) conversion circuit, which adopts the method of constant current source.Precision constant current source resistance measurement accuracy depends largely on the flow through the
3、 measured resistance, when the constant current source with high accuracy, stable voltage measured resistance, can improve the measurement accuracy of resistance. Therefore, the design of a good stability, high accuracy of the constant current source is very important.According to the actualneeds,in
4、 the device selection,considering the influence ofnoise,Wen Piao,design aconstant current sourcewith good stability.1 constant current source is introducedThe basicfunction of a constant current sourceis toeliminate or reducethe power supply voltage,load resistance and theinfluenceof environmental t
5、emperature on theoutput current.The constant current sourceaccording to the adjustmentof different ways,can be divided into directand indirectadjustment ofconstant current sourceadjustableconstant current source.Directadjusting typeconstant current sourcecircuit is simple,the mainpower supplyandcons
6、tant currentdevices,using thenonlinear characteristicof constant current devicesare used to directly adjustthe load current.For example,a constant current diode,but itscurrent valueis limited andstabilityis poor.The indirectadjustmentis a constant currentcircuit composed of electronic tubes, transis
7、tors and other electronic componentstogether constitutethe.For example,feedback OPamplifier based onconstant current source,the use of suchcircuitcan produceexcellentperformanceconstant current source.1.1basic structurefeedbackconstant current sourceFeedback constant current source through thenegati
8、ve feedback effect, to make comparison between the amplifier two input voltage are equal,so as to maintain aconstant output current. This circuit is connected in series with the load change on the adjustment ofthechange of resistanceto compensatethe output current,so it is also called the series adj
9、ustable constant current source. Itmainly consists of a reference voltage source, a comparison amplifier,adjust thesampling resistancepipe,and other parts.Specific work process:through the sampling resistor to the output current into a voltage feedback amplifier input, to compare, in comparison with
10、 the reference voltage, the voltage error amplifier amplified to control the resistance adjusting pipe to adjust the output current, maintain constant output current.1.2basiccircuit modelThere are many specific forms of feedback circuit of constant current source,according to the loadconnection mode
11、of constant current source,divided into loadgrounding typeand loadof floatingtype,because ofthe constant current sourceis designed for the application of digital multiresistance measurement function in the table, and the digital multimeter in measuring electric wirewhen the black pen and sheet resis
12、tance digital multimeter internal circuit board is connected, so the measuredload resistanceat one endis grounded,so thedesignof the constant current sourceshould begrounded loadtype.2 constant current source circuitdesignOn the basis of the design of high precision digital multi function meter meas
13、uring resistor, the resistance profile of different needs of different constant current source, and therefore need to design a 4 constan current output of the constant current source circuit.Combined with the design offeedback constant current source principle, by different samplingresistance value,
14、so as to achieve4differentconstant current sourceoutput.Inthe design of constant current source,a reference voltageselection is very important,itdirectly affects thestabilityof the constant current source.The reference voltagerequirements ofhigh precision,smalltemperature drift,need to choosethe ref
15、erence voltagechipwith low noise.Based on the above requirements, considering the choice of Linear Technology Corporation shunt voltage reference chip LM399, typical output voltage reference value 6.95V. It has the following characteristics: drift coefficient, 0.5ppm/C; dynamic resistance is small,
16、the maximum of 1 ohm;noise voltage effective value of maximum 20 V initial accuracy of2%.LM399 internal thermostatic heater, can improve the effect of temperature drift, stable performance for a long time. The constant current source circuit in the amplifier offset voltage,temperature drift,noisevoltagewill affect theaccuracy of theconstant cur
