Research And Design Of A New Constant Current Device With Low Temperature Coefficient

In the use of many electronic devices,external systems are required to provide a stable current.This device capable of providing a constant current to the load is called a constant current source.As a branch of the constant current source,discrete constant current devices feature of low knee voltage,good constant current characteristics,and simple application circuits.The constant discrete constant current devices have developed rapidly in recent years,and have been widely used in the protection circuits of constant current sources,voltage regulators,amplifiers,electronic instruments,and LED lighting.With the development of the LED industry and the demand for high-performance constant current sources in the application market,discrete constant current devices have been extensively studied,including research on new structures,and related process realization studies.However,the current constant current device products have the problems of high knee voltage and low forward breakdown voltage,and there is still a certain gap from the actual application requirement in terms of temperature stability.The physical structure and working mechanism of traditional constant current devices limit their temperature coefficient to be further reduced.Therefore,it is necessary to explore ways to improve the temperature stability of constant current devices from the physical mechanism.Based on this,this paper aims to design a constant current device to improve the device's current capability and reduce the knee voltage while improving the device's temperature stability.Therefore,a new type of constant current device structure with low temperature coefficient is proposed and verified experimentally in this paper,which introduces hole current to increase the device current capability and reduce the knee voltage,and the low temperature coefficient is achieved by adjusting the hole-to-electron current ratio.According to the proposed constant current device structure,this paper establishes a saturation current model,and combines the relationship between the characteristics of semiconductor materials and temperature changes to derive the expression of the relationship between the constant current value and temperature,which is used to guide the design of low temperature coefficient constant current devices.The Medici and Tsuprem4 TCAD simulation tools were used to simulate and analyze the influence of the key parameters of the device on its temperature characteristics and electrical performance,verify the theoretical feasibility of achieving a low temperature coefficient constant current device,and optimize the key parameters of the device to obtain a tape-out solution.Layout drawing was carried out using Cadence's Virtuoso software,and tape-out verification was performed based on the process platform provided by the partner.A constant current device sample was obtained through the tape-out.The experimental results shows that when the ambient temperature is T=25°C,the constant current value of the designed constant current device is 118 mA,the forward breakdown voltage V_B,F is about 45 V,and the reverse breakdown V_B,R reaches 200 V,and the knee voltage V_K is about 2.7 V.When the ambient temperature T increases from 25°C to125°C,the temperature coefficient is 0.10%/°C,which is lower than that of the constant current device with high constant current that have been reported.