Design Of Key Circuits For Radiation-hard Buck Converter

The advancement of aerospace science and technology is of strategic significance to the development of the national economy and the construction of modern national defense.The power integrated circuit represented by Buck converter is known as the "heart" of power electronic equipment,and is the basis for ensuring the proper operation of aerospace equipment and nuclear equipment.Therefore,the research and design of radiation hard Buck converter and its key circuit is very necessary.Based on the analysis of the radiation mechanism and the existing enclosed layout transistor structure,this thesis proposes a symmetrical square enclosed layout transistor(SS-ELT)structure.The equivalent aspect ratio model of the SS-ELT device is deduced by area division and other methods,and the enclosed layout transistor library is built on the Virtuoso platform based on the 0.18μm standard commercial BCD process.Through standard layout unit drawing and related library file writing,the functions of calling,simulating and drawing layout of SS-ELT device in Virtuoso platform are realized.Carry out tape-out design for SS-ELT devices of different sizes and corresponding normal MOS devices.The chips are tested in radiation and non-radiation environments.Furthermore,the radiation hard performance of SS-ELT devices and the accuracy of the equivalent aspect ratio model are verified.The test results show that the calculation error of the equivalent aspect ratio model is stable at around 5%.Under the radiation condition of a dose rate of 50rad(Si)/s and a maximum total dose of 1Mrad(Si),the threshold voltage of the normal MOS device continuously drifts negatively with the increase of the total dose,and the off-state leakage current reaches the order of 10μA at 100krad(Si),which show the loss of fundemental function.In coparision,the SS-ELT devices can still work normally under a total dose of 1Mrad(Si),and the threshold voltage remains basically unchanged when the total dose increases.What’s more,the maximum off-state leakage current of SS-ELT devices is still less than 0.1μA,showing superior radiation tolerance.On the basis of the SS-ELT device library,three key circuits of the Buck converter chip including the reference circuit,the pre-regualtion circuit and the internal-chip LDO,are designed to achieve the purpose of radiation hard.Measures such as adopting current mode reference architecture,replacing bipolar by dynamic threshold-voltage MOS(DTMOS),and choosing SS-ELT NMOS devices are taken to improve the radiation tolerance of the circuits.The simulation verification of the electrical performance of the circuit’s Corner characteristics,loop stability,temperature characteristics,and voltage adjustment capabilities are completed before tapeout.After that,the chip was COB packaged and tested.The result shows that the output voltage of the reference circuit fluctuates by 1m V within 0.2%.The pre-regulation circuit has a wide input range of 6V-32 V,and the output fluctuation range is less than 28 m V.The load current of the LDO circuit changes from 10μA to 5m A,the output voltage is stable around 1.8V,and the maximum fluctuation amplitude is 20 m V,whose percentage error is around 1.1%.The input voltage of the LDO circuit changes from 6V to 20 V,and its output voltage is still stable at 1.822 V,which deviates from the design value by 1.2%.