CMOS Pipeline ADC/the Design Of Band-gap Voltage Reference Circuit

ADC is an indispensable key component in an integral system development. Theband-gap voltage reference which provides stable voltage and current is obviouslyimportant for the entire system as well. Consequently, it is significantly important todevelop a gap voltage reference with high-performance.In normal band-gap voltage reference circuit, the voltage with positivetemperature coefficient is produced from△VBEbetween basal pole and emitter of twosame PNP bipolar transistors. Because of the input offset voltage VOScaused by usageof operational amplifiers, the precision of output reference voltage is impaired. Thisarticle presents a type of high performance band-gap voltage reference structure withcombination of first-order temperature compensation and NPN bipolar by analyzingthe principle of normal CMOS band-gap reference circuit.△VBEproduced via NPNtype triode amplifier in this article, which reduces the influence to circuit precision byamplifier offset voltage. Feedback circuit improves power supply rejection ratio. Andthe active circuit solved the problems of degeneracy. The active circuit willautomatically switch off when band-gap reference circuit start completely, whichavoids the influence to the precision of band-gap reference circuit by active circuit.This circuit is with simple structure, high power supply rejection ratio, small changeof output voltage caused by temperature.The band-gap reference is implemented in SMIC0.18um CMOS process. Incondition with first-order temperature compensation, pre-simulation via Cadence andwith0~1.8V input, the band-gap reference output voltage is1.20V. In the range from-40℃to+120℃, maximum deference of output voltage is1.25mV, temperatureconfidence is7ppm/℃. In frequency range1~1GHz, power supply rejection ratio(PSRR) is-85dB. Drawing layout and simulation test shows the temperaturecoefficient of post-layout simulation is11.25ppm/℃which is not big different withpre-simulation; PSRR of post-layout simulation is71.2dB which is lower but alsomeet the normal application requirements. Generally, the band-gap reference of thisarticle fulfills the requirements of the12bits100MHz ADC completely.