Study And Design Of Reference Voltage Circuit In 18 Bit 20Ms/s Pipelined ADC

The reference voltage circuit widely used in mixed signal integrated circuits is the key module of integrated circuit system.In the high-speed and high-precision pipelined ADC,the reference voltage circuit with high-precision and high-speed transient response ability is an essential part of ADC circuit design.According to the theoretical analysis of the pipelined ADC circuit structure,working mode and reference voltage,a reference voltage circuit applied to 18 bit 20 MS/s pipelined ADC is designed in this dissertation,which is realized by a high-precision bandgap reference circuit and an output buffer with high-speed transient response ability.Firstly,referring to the analysis of key design points of bandgap reference circuit,a voltage summation type bandgap reference circuit based on the first-order temperature compensation is designed with low temperature coefficient,high power rejection ratio and low output noise in-40 ℃～85 ℃.The bandgap reference circuit provides a stable reference voltage for the output buffer circuit of latter stage.Secondly,with the circuit structure and working mode of 18 bit 20 MS/s pipelined ADC,the complex changes of output buffer circuit load in the process of ADC quantization are analyzed.An output buffer circuit with common source push-pull output and voltage negative feedback structure is designed,which increases the sensitivity of output buffer circuit to the change of reference voltage.Miller compensation and zero compensation technology are used to increase the negative feedback loop bandwidth of output buffer circuit to improve the response speed of the circuit,and reasonably design transistors size to optimize the noise performance of the circuit.Finally,based on the 180 nm 1P6 M CMOS process and the Cadence platform,the circuit layout is designed and verified to back-end simulation.The overall ADC circuit layout area is2.5 mm×5.0 mm,in which the reference voltage circuit layout area is 0.2 mm×1.05 mm.The simulation results show that the output voltage temperature coefficient of the bandgap reference circuit is 5.337 ppm/℃ in-40 ℃～85 ℃ and,the power rejection ratio is 75.34 d B in the low frequency(10 KHz)with output noise 64.21 μV.The negative feedback bandwidth of the output buffer circuit is 90.68 MHz,with 61.27° phase margin,and 115.03 μV output noise.The overall ADC used the designed reference circuit has an effective number of bits 16.20 bit,the signalto-noise ratio 99.34 d B and the spurious free dynamic range 108.40 d Bc at 20 MHz sampling frequency and 859.375 KHz input signal frequency.