Low Voltage Bandgap Reference Circuit

Band-gap reference circuit, which concludes voltage reference and current reference, is an critical part of SOC. It can be widely used in many blocks such as power management chip, temperature sensor, ADC, DAC, and memory, because of its low temperature coefficient,high PSRR,Jow noise,low linear adjustment rate and so on.Based on the advantages above,band-gap voltage reference becomes a hot area of research.With the development of integrated circuit, the minimum feature size of newer CMOS processes is reducing to deep sub-micron, IC becomes increasing integrated,the power supply voltage is decreasing,the threshold voltage limits the application of low supply voltage operation.It will be a bigger challenge to the design of band-gap reference.Therefore,band-gap voltage references which can operate with low supply voltage are in high demands and the research is very meaningful.The paper introduces the research background and significance of the band-gap reference in the beginning,and states the research status at home and abroad.at the same time,it proposes the overall structure.Then,we analyze the theoretical basis of the band-gap reference,including its performance indexes,a CTAT voltage, a PTAT voltage and a typical band-gap reference circuit.Finally,we present two low voltage band-gap references which are the core of the article.In this paper,we focus on two low voltage band-gap references,one is based on current mode,the other is based on DTMOST.The core structure of the low voltage band-gap reference which based on current mode is the sum of current.The two-stage operational amplifier in this circuit forces the two input voltages to be equal.We use current mirror structure to provide stable biasing voltage and current.In the meantime,we add a RC filter to enhance the PSRR and reduce the noise.So,we can get a low voltage band-gap reference with high accuracy. This band-gap is appropriate for low voltage application and has a high PSRR.We can generated a temperature-independent voltage as long as a suitable ratio coefficient is chosen.The output voltage of the other band-gap reference is the sum of a CTAT voltage and a PTAT voltage.lt will generate a low temperature coefficient voltage.Meanwhile,a unity-gain buffer,which can enhance drive capability of the output, is added to the output of this band-gap circuit. We also use the feedback technology to increase the value of PSRR.In this paper,we present a multistage band-gap reference which can achieve high accuracy by using two layer of band-gap reference structures.It also uses DTMOST in order to generate a highly accurate band-gap voltage reference at low voltage operation.Therefore,this MOST is able to operate band-gap voltage reference at lower supply voltage.This circuit is not only a example of low voltage operation,but also a solution of low power application.In traditional low voltage band-gap reference,if we want to achieve low power,we should use high value resistors.The area will increase because of the increasing cost of matched resistors.In an OVF circuit,matched resistors are replaced by matched transistors,this method not only improves the matching accuracy,but also reduces the power and the entire die area.It is the balance of low power and small area.The two band-gap references in this paper were fabricated in a 0.18-um CMOS technology.We use cadence to simulate the two band-gap references.,including the simulation of temperature coefficient,the simulation of PSRR,the simulation of linear adjustment rate.Then we adjust the parameters and structures of the circuits to get the optimum performance of circuits.Temperature coefficient and PSRR are very important parameters of the band-gap.Temperature coefficient describes the temperature dependency of the output voltage of this band-gap circuit.In this technology,the simulation temperature range is-40℃～125℃.PSRR is a AC parameter which represents the inhibiting ability of power noise in small signal condition.With the addition of a small AC voltage on power,we can get the PSRR at the frequency range of 1 Hz to 100MHz.