Two Wire 4～20mA Current Converter Design

The two wire 4~20 m A current converter plays an important role in the conversion and transmission of electric signal,which converts the input voltage signal into the output current signal.The weak voltage signal is susceptible to interference during transmission,while the milliampere current signal is less susceptible to interference during transmission,and the voltage signal is attenuated due to the voltage drop across the distributed resistance of the transmission line,and the transmission line resistance also changes when the temperature changes,so the current signal is more stable than the voltage signal and is more suitable as a transmission signal.The data signal collected at the industrial site is voltage signal,which need to be converted into current signal by the current converter before it can be accurately transmitted to the control room from a long distance.Therefore,the current converter plays an important role in the process of electric signal conversion and transmission.It can be applied to various industrial fields such as remote pressure &temperature sensor,remote data acquisition,etc.,so the research on the current converter is very important.In this paper,the current converter chip is deeply studied.Based on the 2μm+40V Bipolar process,the two wire 4~20m A current converter for long distance signal transmission is designed.Based on the design goals and the conventional current converter circuit structure,the expected design specifications of the main parameters were established.The circuit system architecture design of the two wire 4~20m A current converter is completed,and each sub-module was divided,and the role of each sub-module in the two-wire current converter circuit system is defined.On this basis,the transistor-level circuit designs of the common base op amp,low output impedance op amp,high swing op amp,current source circuit,bias circuit,voltage regulator circuit and ESD protection circuit module are completed.Using spectre simulation tool to simulate and optimize each module circuit and system circuit of the current converter,and determine the parameters of the triode,diode,resistor,capacitor and other devices in each module circuit to obtain the current converter circuit that meets the expected design specifications.Use the Virtuoso Layout Editor tool to complete the current converter layout design,then use Calibre to complete the DRC,LVS,ERC and other inspections of the layout.Extract the parasitic parameters of the layout and use the ocean script to complete the circuit of post simulation and verification,and optimize the layout.Finally the wire 4 ~ 20 m A current converter that meets the requirements is finished.The simulation results show that the current converter can stably convert the input signal to4-20 m A current under the supply voltage of 15~36V and ambient temperature-40~85℃.The input voltage signal range that needs to be converted can be adjusted by adjusting the external resistance.The maximum deviation of zero output is 32.99μA,and the deviation of output range is up to 99μA.All parameters meet the expected design goals.