Design Of High-Precision Band-gap Reference Voltage Source With Over-Temperature Protection Function

With the continuous advancement of science and technology,the functions of electronic products are more and more complete,the volume is getting smaller and smaller,the weight is lighter and lighter,and it is easy to carry,which makes people's life rich and colorful.The most advanced of electronic products is the upgrading of smart phones,the use of functions is becoming more and more abundant,and the communication is more and more convenient.The realization of these functions benefits from the development of integrated circuits,and the line width of chip manufacturing processes is becoming more and more Small,more integrated.Band-gap reference voltage source,as a significant module in digital integrated circuit and analogue integrated circuit,performs its favorable stability and accuracy.Hence,it can provide reliable reference voltage of circuit system.With a rapid development of integrated circuit,the performance requirements towards reference voltage have become increasing.To satisfy work requirements of system better,an improvement trend on reference voltage is continually forwarding in low-power dissipation,high stability,high precision and other relevant aspects.Reference voltage source in work process,can easily suffer impacts by multiple factors of which the most important two are temperature and supply voltage.The fundamental of band-gap reference voltage source is that will not be affected by temperature which is formed by addition of the bipolar transistor base — emitter voltage with negative temperature coefficient and thermal voltage with positive temperature coefficient.In addition,power supply noise also has great influence on reference voltage.Therefore,it is extremely urgent to settle these two factors.Besides,reference voltage source is likely to be affected by external temperature and heats generated in its work process.When the rising temperature reaches beyond the temperature range of reference voltage source,voltage source will be burned by the excessive temperature.To solve the over-temperature influence is also a critical factor in current reference voltage source design.At present,four kinds of band-gap reference source circuits are most widely used,including Kuijk,Widlar,Brokaw and Banba.In consideration of output reference voltage below 1.25 V,flexible design,precise output reference voltage and other factors,Banba reference source circuit is selected in this paper.As the traditional Banba reference source is provided without temperature compensation,the output reference voltage can be easily impacted by temperature.The settled reference voltage is not stable,which cannot meet requirements for design.Therefore in this paper,we add high-order temperature compensation on a basis of the traditional reference source by compensating reference circuit with MOS tube on drain current generated in subthreshold area,which can reduce temperature affects.Since the NMOS transistor operates in the subthreshold region to generate a drain current with a positive temperature coefficient,the reference voltage can be compensated at a high temperature range;instead,a drain temperature with a negative temperature coefficient generated by the PMOS transistor operating in the subthreshold region is utilized.The reference voltage is compensated in the low temperature range;different MOS tubes can be used to compensate separately in the high temperature range and the low temperature range,so that the influence of temperature can be reduced.In order to reduce the influence of power supply voltage noise on the reference source,and in order to obtain a higher op amp gain,this paper uses a two-stage op amp.The first stage uses a stacked cascode structure,which has a large output resistance.Therefore,a higher gain can be obtained,and the second stage is a CMOS op amp.In order to ensure that the reference voltage source can not be burned at too high temperature,this paper designs an over-temperature protection function to monitor the temperature change in real time by using a temperature-sensitive bipolar transistor.When the temperature is too high,the over-temperature protection device is activated.The reference circuit is turned off.When the temperature drops to a certain value,the over-temperature protection function is turned off and the reference circuit is started.The simulation results show that under the working voltage of supply voltage 5.0V,the settled reference voltage before compensation is 1.199V;the reference voltage changes by 2.545 mV when temperature range is kept at-40? to 125?,and the temperature coefficient is 12.9ppm/?.The higher temperature coefficient is,the more easily the voltage will be influenced by temperature.After temperature compensation for the traditional reference source,the simulation results show that under the same working conditions,the output reference voltage has changed by 0.373mV;the temperature coefficient is 1.8ppm/?,and output reference voltage is 1.199 V.Obviously,the temperature coefficient has reduced a lot with a relatively low effect by temperature and a better stability.In the process of over-temperature protection simulation,the function will start when temperature reaches 150?,and power source will be turned off;the function will stop when temperature drops to 135?,and the power will start up and circuit can work normally.