Bandgap Reference Bandgap Reference VoltageVoltage

SVTH:Đặng Thanh TiềnSVTH:Đặng Thanh Tiền

Bandgap Reference VoltageBandgap Reference Voltage

AbstractAbstract IntroductionIntroduction Circuit of the BGRCircuit of the BGR SimulationSimulation ConclusionConclusion ReferencesReferences

AbstractAbstract A bandgap reference voltage is an essential A bandgap reference voltage is an essential

component of an analog-to-digital converter.component of an analog-to-digital converter. BGR is often used to supply a reference BGR is often used to supply a reference

voltage which is compared with other voltage which is compared with other voltages.voltages.

The main design criteria for this project is to The main design criteria for this project is to achieve PSRR above 60dB and a variation less achieve PSRR above 60dB and a variation less than 3% resulting from temperature changes than 3% resulting from temperature changes between 27℃ and 85℃.between 27℃ and 85℃.

AbstractAbstract

Figure 1 Circuit of BGRFigure 1 Circuit of BGR

IntroductionIntroduction A bandgap reference voltage with low A bandgap reference voltage with low

sensitivity to temperature and supply voltage sensitivity to temperature and supply voltage is commonly required in analog or digital is commonly required in analog or digital circuits.circuits.

The base emitter junction used as a core The base emitter junction used as a core component of the bandgap reference is the component of the bandgap reference is the most popular approach.most popular approach.

The general bandgap reference voltage is The general bandgap reference voltage is described by a linear combination of base-described by a linear combination of base-emitter voltage.emitter voltage.

IntroductionIntroduction We can compensate temperature dependent We can compensate temperature dependent

voltage by adding a positive-TC voltage to a voltage by adding a positive-TC voltage to a negative-TC voltage.negative-TC voltage.

The positive-TC voltage comes from the The positive-TC voltage comes from the voltage difference between two pn junctions. voltage difference between two pn junctions. The Fig. 2 shows the reason behind positive-The Fig. 2 shows the reason behind positive-TC voltage.TC voltage.

IntroductionIntroduction

Figure 2 Generation of temperature independent voltageFigure 2 Generation of temperature independent voltage

IntroductionIntroduction Ideally, adding a positive-TC voltage to a Ideally, adding a positive-TC voltage to a

negative-TC voltage can realize a zero negative-TC voltage can realize a zero temperature coefficient 1.26V at the room temperature coefficient 1.26V at the room temperature.temperature.

The reference voltage is required to be robust The reference voltage is required to be robust to the power supply voltage.to the power supply voltage.

An easy way to improve power supply An easy way to improve power supply rejection ratio (PSRR) is to increase the open rejection ratio (PSRR) is to increase the open loop gain.loop gain.

Circuit of the BGRCircuit of the BGR Start Up CircuitStart Up Circuit Differential AmplifierDifferential Amplifier BandgapBandgap

Start Up CircuitStart Up Circuit The transistors have two states, on and off, The transistors have two states, on and off,

when power is provided.when power is provided. Since M13 is also in saturation, it provides a Since M13 is also in saturation, it provides a

sufficient gate voltage for M15 to turn on.sufficient gate voltage for M15 to turn on. When M15 is on, a small current will flow When M15 is on, a small current will flow

through Op Amp and enable the entire circuit.through Op Amp and enable the entire circuit. M14 will turn on and sink all the current from M14 will turn on and sink all the current from

M13 and disable M15.M13 and disable M15.

Start Up CircuitStart Up Circuit

Figure 3 Start up circuitFigure 3 Start up circuit

Differential AmplifierDifferential Amplifier We use an operational amplifier for this We use an operational amplifier for this

purpose.purpose. It is composed by the common-source stages It is composed by the common-source stages

with diode-connected loads.with diode-connected loads. Its output provides a bias for the entire Its output provides a bias for the entire

circuits, and a feedback loop is formed.circuits, and a feedback loop is formed.

Differential AmplifierDifferential Amplifier

Figure 4 Differential gain stageFigure 4 Differential gain stage

BandgapBandgap The voltage difference between the two pn The voltage difference between the two pn

junctions is the positive-TC voltage.junctions is the positive-TC voltage. A PTAT current can be copied from the A PTAT current can be copied from the

current mirror and can be adjusted by current mirror and can be adjusted by changing the width of M12 or the resistance changing the width of M12 or the resistance of 1 R .of 1 R .

BandgapBandgap

Figure 5 Bandgap circuitFigure 5 Bandgap circuit

SimulationSimulation The reference voltage is required to be 1.26V The reference voltage is required to be 1.26V

at the room temperature.at the room temperature. The base-emitter voltage is 0.75V at 25℃The base-emitter voltage is 0.75V at 25℃ We can set the PTAT current going through 2 We can set the PTAT current going through 2

R to be 54 µ AR to be 54 µ A

SimulationSimulation

SimulationSimulation The exact PSRR and reference voltages for The exact PSRR and reference voltages for

certain values are depicted in the Table 1.certain values are depicted in the Table 1.

ConclusionConclusion A design using bandgap core circuit with Op A design using bandgap core circuit with Op

amp and start-up circuit is presented and amp and start-up circuit is presented and simulated.simulated.

The overall performance of the BGR circuit is The overall performance of the BGR circuit is summarized in the Table 2.summarized in the Table 2.

ConclusionConclusion

ConclusionConclusion Comparisons with other design are shown in Comparisons with other design are shown in

table 3.table 3.

ConclusionConclusion

ReferencesReferences [1] D. F. Hilbiber, “A new semiconductor voltage standard”, [1] D. F. Hilbiber, “A new semiconductor voltage standard”,

ISSCC Digest Technical Papers, vol. 7, pp. 32-33, 1964 ISSCC Digest Technical Papers, vol. 7, pp. 32-33, 1964 [2] David Jones, “Analog Integrated Circuit [2] David Jones, “Analog Integrated Circuit [3] K. Lasanen, V. Korkala, “Design of a 1-V low power [3] K. Lasanen, V. Korkala, “Design of a 1-V low power

CMOS bandgap reference based on resistive subdivision”, CMOS bandgap reference based on resistive subdivision”, IEEE IEEE

[4] T. L. Brooks and A. L. Westwick, “A low-power [4] T. L. Brooks and A. L. Westwick, “A low-power differential CMOS bandgap reference,” in ISSCC Dig. Tech. differential CMOS bandgap reference,” in ISSCC Dig. Tech. Papers, Feb. 1994, pp. 248–249. Papers, Feb. 1994, pp. 248–249.

[5] Behzad Razavi, “ Design of Analog CMOS Integrated [5] Behzad Razavi, “ Design of Analog CMOS Integrated Circuits”, cGRAW-Hill, 2000 Circuits”, cGRAW-Hill, 2000