The Research And Design Of Voltage Reference In High Speed High Precision ADC

The bandgap voltage reference circuit is a very important block in analog integrated circuits, which is applied widely in DC_DC converters, RF, espically in ADC and DAC. The bandgap voltage is applied to not only the comparative reference voltage, but also the biased voltage. Based on SMIC CMOS 0.18μm and 1.8V power supply process, a bandgap voltage reference circuit applied in 10bit, 180MS/s pipelined ADC is investigated and designed. In order to satisfy the requirement of the ADC,the variation with the temperature (-55℃-125℃) and the supply voltage(1.6V—2.0V) must be less than 0.5LSB(=0.49mV), namely that the temperature coefficient must be less than 5ppm/℃, and the Power-supply rejection ratio(PSRR) must be less than 1.25mV/V(-58dB).In this paper, firstly, the principle of voltage reference is analyzed and the architectures are summarized, including conventional architectures, low voltage architectures and nonlinear temperature compensation. Then the system of voltage reference in Pipelined ADC is designed, including the bandgap generator circuits and the circuits which deal with the bandgap voltage output. In the first part, the system of the bandgap voltage reference is designed, and some parameters, including the voltage, the current, resistor, etc, are fixed on the principle of temperature compensation; the influence of operation- amplifier on voltage reference is analyzed, and at the same time, a high-gain two-stage operation- amplifier is designed; Then the startup circuit and the layout of the voltage reference circuit is designed. The results are simulated by Hspice. The gain of operation- amplifier is above 80 dB, the variation of the output voltage with temperature (-55℃-125℃) is 4.87ppm/℃, and the variation of the output voltage with power supply between 1.6V and 2.0V is less than 1mV/V (-66dB). In the second part, the application of voltage reference circuits is analyzed, a model for voltage reference in ADC is proposed, and the buffers are designed.The bandgap reference is taped out and tested, the result is not good,then the reasons are analyzed. Finally some improvements for the bandgap voltage reference are designed, including the nonlinear temperature compensation, the biased circuit for high PSRR, and the architecture for low voltage.