The Design Of High Performance Current Transmitter

After collecting physical parameters such as temperature,pressure and velocity,the detection process parameters are usually converted to standard analog electrical signals for transmission.There are two ways to communicate analog signals,one is voltage and the other is current.The transmission of voltage signals in the long distance is susceptible to interference from external noisy environment,and parasitic resistance of transmitter output,transmission lines and loads will cause voltage signal loss,resulting in voltage signals distortion.In addition,most industrial inverters and process controllers operate in the form of voltage.In order to avoid these problems,a current transmitter is usually used to transfer voltage signals to current signals for transmission.Based on the in-depth study of the basic principle of the current transmitter,a low-power and high performance current transmitter using bipolar technology is designed for long-distance transmission.The design of the regulator,the biasing circuit,the current source circuit and the system circuit is completed.A band gap reference is used in the regulator to improve the voltage stability.Temperature compensation and emitter follower are used in the biasing circuit to improve the output accuracy.Temperature compensation and feedback control loop are used in the current source to improve the accuracy and stability.The simulation results show that every sub_circuits meets the design specifications.On this foundation,the system circuit in transistor level is designed and the layout succeeded in DRC and LVS.Finally,the netlist file containing parasitic parameters is extracted by using Calibre PEX,and the post-simulation of the key modules and systems are carried out.The simulation results are obtained when the power supply is 15-36 V and the temperature is-40~85?.The regulated voltage circuit can generate a constant voltage of 5.1V,and the precision error is less than 0.78%.Bias circuit produces bias voltage of 4.1V and 1.25 V,and the precision error is less than 0.87% and 0.88% respectively.The high precision current source can generate current of 250?A,250?A and 100?A,and the precision error is less than 0.48%,0.54% and 0.90% respectively.The current transmitter realize V/I conversion that converting the input voltage of 0~10V to the output current of 4~20m A,the maximum error of output current range is 0.58%,and the maximum error of zero output is 37.78?A.The simulated result proves that this current transmitter is in accord with requirement.