Voltage references using mutual compensation of mobility and threshold voltage temperature effects

A voltage reference is an essential building block of many analog and digital circuits. The performance of a reference is gauged by the maximum variation in its allowable operating conditions. One of the most important specifications of a reference is its temperature drift. Therefore, special attention should be paid by the designer to the thermal behavior of a voltage reference.; In this thesis, three new voltage reference circuits are proposed and designed in 0.18-mum technology. Our goal has been to design CMOS voltage references with better temperature stability compared to that of existing voltage references. First, a voltage reference is presented which takes advantage of summing the gate-source voltages of two diode-connected transistors biased by temperature-stable currents. The temperature coefficient of the output voltage of this reference is shown to be 28 ppm/°C over the temperature range of -50°C to 150°C. Next, the temperature behavior of the gate-source voltage of a CMOS transistor biased by a current, which is proportional to absolute temperature (PTAT), is investigated. It is shown that the temperature coefficient of the gate-source voltage of the transistor can be altered by adjusting the parameters of the PTAT current source. This idea is then applied to the design of two temperature-independent voltage references. The first reference consists of a PTAT current source and a diode-connected transistor. Simulation results show that the temperature coefficient of this reference voltage is 4 ppm/°C over the range of -50°C to 150°C. The second reference takes advantage of summing the gate-source voltages of two NMOS transistors biased by PTAT currents. The last two references show a temperature coefficient of 4 ppm/°C over the range of -50°C to 150°C and can operate with a power supply below 1 V. The simulation results for this voltage reference show a temperature coefficient of 4 ppm/°C over the range of -50°C to 150°C. The operation of all the circuits are also justified analytically.