Low Voltage, Low-power High-precision Reference

The bandgap voltage reference circuit is a very important block in analog integrated circuits, which is applied widely in Analog to Digital Converter (ADC), Digital to Analog Converter (DAC), Power management circuits and memories. With the popular use of electronic system powered by battery, the power dissipation, speed and precision of ADC are more important. Based on CMOS 0.18μm and 1.8V power supply process, a bandgap voltage reference circuit applied in 12bit, 100Msps pipelined ADC is investigated and designed. In order to satisfy the requirement of the ADC, the temperature coefficient with the temperature (-40℃～85℃) must be less than 6.84ppm/℃, and the variation with the supply voltage(1.6V～2.1V) must be less than 1860ppm/℃.This paper presents a general introduction on the bandgap reference firstly, including its performances and principle. A novel curvature-compensated CMOS Bandgap Voltage Reference, which utilizes two first order temperature compensations generated from the nonlinearity of the finite current gainβof vertical PNP bipolar transistor, is presented. This reference is suitable for low voltage by exploiting the superposition of curvature-down and curvature-up currents, which uses a cascode structure to improve the high power supply rejection ratio (PSRR). This is significant in low power applications where resistors need to be large. Thus, a resistive Y-network is utilized to reduce the area. The influence of operation amplifier on voltage reference is analyzed, and at the same time, a high gain two stage operation amplifier is designed.During the design, the application of voltage reference circuits is analyzed, a model for voltage reference in ADC is proposed and the relationship between the buffer's gain-bandwidth, transconductance and the speed, resolution of ADC is obtained. The designed buffer has both a low temperature coefficient and a capability of rejecting high frequency noise.The circuit is simulated with the simulation tool of Cadence. The variation of the output voltage with temperature (-40℃～85℃) is 1.77ppm/℃,and with power supply between 1.5V and 2.1V is less than 864.1ppm/V. At the room temperature (25℃), its PSRR is about 63dB and the start-up time is 61ns. Under 1.5V to 2.1V power supply, the output change of voltage is 0.43mV/V. As the process corners vary, the power consumption is 0.65mW at most and 0.46mW at least, under the condition of 1.8V power supply. The whole circuit design fulfils the requirements of the program mentioned above.