The Design Of Two-Wire Transmitter Interface Chip Based On Temperature Compensation Technology

Two-wire 4-20mA system transducers are widely used in the industrial field, whose main function is to transport the data measured in industrial field to the control room, playing an important role in modern industrial control. Two-wire instruments are mostly based on the application of dedicated chip design. However, at present, the designing technology of the chips for such instruments is mastered by only a few foreign semiconductor manufactures. Furthermore, although many research institutes in our country have carried out considerable research on the designing of the dedicated chips for two-wire transducers, standard products with satisfying performance index are still not available. In addition, the temperature at the industrial field varies in a wide range, which requires an excellent temperature characteristic of the two-wire transducers. When the temperature varying from -40 ℃ to +105 ℃, loop current accuracy should be limited within one-thousandth. Two-wire transducer ASIC design relies on a number of key technologies, and the most critical one is the current reference in the chip with low temperature coefficient. Foreign products generally adopt low temperature coefficient thin-film resistors based on special processing to achieve accurate current reference. However, currently domestic process does not support such low temperature coefficient thin-film resistor, designing an accurate current reference that satisfying the design need is extremely difficult.In this paper, a loop powered two-wire 4-20mA system transducers based on temperature compensation technology is proposed, which is realized domestic Huahong HHNEC GE0.35μm processing. This design mainly contains these following key technologies. First, a novel temperature compensation method based on Gaussian current unit is proposed, which solves the design problem of the high precision and low temperature coefficient bandgap voltage reference. When temperature ranges from -40 ℃ to +105℃, the temperature coefficient can reach 1ppm/℃. On this basis, a special Ⅴ-Ⅰ conversion circuit with temperature compensation function is designed to solve the current reference design problem. In the range of -40℃ to +105℃, reference current drift is less than 0.1%, better than similar foreign products. To eliminate the influence of the loop voltage fluctuations on the chip precision instrument, a wide input voltage range, high power supply rejection ratio (PSRR) LDO is also designed. The PSRR owns less than -90dB value under 1KHz, which are -65dB and -70dB for 100KHz and 1MHz, respectively. Based on previous work, the ΣΔ-DAC has been improved, the non-linear error of the output current is reduced at the same level with foreign products. To address the impact of process variation, digital trimming technology and data fuse solidification technology is utilized in our article.Simulation of the system is carried out with Hspice software and the results indicate, in the whole process corner conditions and-40 ℃ to+105℃ temperature range, the perform-ances of the design chip have reached or even exceeded similar foreign products. Layout of our circuit has passed DRC and LVS verification, the layout area is 2500μm×2260μm.