Design Of A 4-20mA Two-wire Transceiver Integrated Circuit System Based On GMR Sensor

In industrial control, there are two ways to measure the signal of magnetic field, pressure and temperature. The one way is to use field bus to transmit the signal to the remote PC. Another one method is to transmit the signal to long distance by converting the detected signal to current signal.When the voltage signal transmits in long line, it can be affected by noise. Moreover, the transmition line’s distribution resistance could cause voltage drop, which makes the signal distortion. In order to avoid these problems, now widely used in industry is 4 ~ 20 mA current to transmit signal.Giant magnetic resistance(GMR) sensor exhibit excellent properties, e.g. high sensitivity, low nonlinearity and small hysteresis, and can be used widely in the industrial application. Based on the industrial application of GMR sensor, this text designs a 4 ~ 20 mA two-wire transceiver system. In the detection end, the V/I circuit converts the GMR’s output voltage signal to 4 ~ 20 m A current signal for long distance transmition. In the receiving end, the I/V circuit recovers the 4 ~ 20 mA current signal to voltage signal without distortion. Based on CSMC 1μm40V HVCMOS process,the system circuit is designed and simulated with the Tanner Integrated Circuit Design software.The chip in the detection end includes conditioning circuit and V/I convert circuit. The conditioning circuit consists of an instrument amplifier. It’s CMRR is 80.645 dB at unit voltage gain. The V/I converting circuit’s span error is 0.0113%, nonlinearity is 0.0106%, slew rate is 38 mA/μs. In the receiving end, the I/V converting circuit’s span error is 0.01%, nonlinearity is 0.005%. All of the circuits can meet the design requirement, and the system transmits the GMR detected signal to long distance without distortion. After the system circuit is designed, the layout of the circuit is also designed.We only flow the low voltage core part of the V/I conversion by MPW. The management circuit using external means. The sample chip is packaged by COB. By tested, the circuit’s up slew rate is 2.67 mA/μs, and the down slew rate is 0.534 mA/μs, the current gain is about 103. There are some deviations between the tested results and the simulation results, but the tested results can meet the design requirement.