| The integrated-circuit industry is an industry of high technic and high investment. Our country starts to develop A/D & D/A converter since 70's, however, its fund and technology cannot compare with America's and Japan's and so on. The 8-bit and 12-bit D/A converter's settling time are 5ns and 200ns respectively, achieveing 80's international similar product's level. But product that can enter the commodity market and abundantly supplied according to user's demand is not many. One of the reasons is that overseas advanced products occupy the domestic market. As a result, our country's A/D & D/A converter have no time to walk along"the study curve", and are difficult to enter virtuous circle. But now, high-speed and high resolution A/D & D/A converter are turned to be one of the most important things in determining performance of advanced electronic equipment or system, such as radar,sonar,wireless telecommunication,high performance controller and driver, etc. So, it's very important to accelerate the research and development of A/D & D/A converter.In the situation, designing a high-accuracy and high-speed D/A converter is very important and significative. After one year, we success to design SDA87HA 12-bit output voltage D/A converter.SDA87HA 12-bit D/A output voltage converter is designed according to ADDAC87 12-bit D/A output voltage converter which is belong to AD corporation. In order to achive the goal of high-accuracy and anti-jamming, we decide to adopt bipolar transistors in the whole circuit. According the technology level of the 24th institute of Chinese electronic science and technology combine corporation, we decide to adopt the B6035 bipolar technology of the institute. The minimum character size of the technology is 6μm,the thickness of the extensive layer is 12μm, the rate of resistance is 2.5Ωcm.SDA87HA 12-bit D/A output voltage converter adopt the buriedZener Reference instead of the common Zener Reference. The buried Zener Reference's stability and output current is better than the common's. The reference dosen't not supply for the D/A converter with 6.3V reference voltage,but also supply for the date input , voltage-current converting,and the output of amplifier with the offset voltage.SDA87HA 12-bit D/A converter's weighed resistance network adopt segmented type, because D/A converter's weighed current is produced by apiece emitter Constant Current Source with the proportion of 2n. That is to say, apiece emitter's area and resistance connected to the emitter are designed with the proportion of 2n. In practice, when the proportion exceeds 1:8, the accuracy is hard to ensure to 12-bit D/A converter.We design a zener Complementary Current Switch, the switch greatly improves the speed of normal switch.The operation amplifier adopts the bipolar technology. We pay more attention to the operation amplifier, because the operation amplifier is a very important factor of the whole circuit.The D/A converter has many output forms and ranges. The ranges include 0～5V,0～10V,-2.5V～+2.5V,-5V～+5V,-10V～+10V. According to the design experience, we make the laser trimmed resistance because the problem of accuracy which is caused by the resistance network, output feedback resistors and so on.The beginning of this article mostly focus on the introduction, analysis and discuss of the theory. The following part mostly design and simulate the circuit.Through the simulation and test of the fourth chapter, the result indicates the D/A converter which we have designed achieves the anticipative goal.The design process of the whole circuit adopt the Composer of the Cadence, and simulate process adopt the SpectrE. At the end of thisarticle, we give the layout of the chip made by the 24th institute, whose effective area is 5.7mm×4.6mm, and has 450 devices integrated on it. The consumption of the chip is 300mW, the temperature range in which the chip can work is - 55℃～+125℃, and the chip has been successfully produced. |
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