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Transcript of CMOS BANDGAP REFERENCED BIASING CIRCUITS - İTÜweb.itu.edu.tr/~yilmazeru/Bandgap.pdf · CMOS...
CMOS BANDGAP REFERENCED BIASING
CIRCUITS
www.vlsi.itu.edu.tr 29.03.2010
1
UMUT YILMAZER504091261
Electronic Engineer
Outline
� Introduction
� Bandgap Reference Circuits• PTAT Current Generation
• CMOS Parasitic BJTs
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• Offset-Speed and Noise Issues
� Design Examples
� Conclusion
Introduction
� There is no ideal voltage or current source!
� High Quality Reference
� Independent of supply voltage � eg: Vdd: 1.8V�2.3V
Independent of process variations
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� Independent of process variations� BJTs: β: ±30%
� MOS: µ: ±10%, Vth: ±100mV
� Resistors: R: ±20%
� Capacitors: C: ±5%
� Inductors: L: ±1%
� Independent or well-defined temperature behavior� eg: T: -25ºC�0ºC�25ºC�75ºC
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Bandgap Reference Circuits
� Target: A fixed dc reference voltage that does not change with
temperature.
� High Power Supply Rejection Ratio and Low Temperature Coefficient
VT:kT/q : PTAT
VBE: CTAT
PTAT+CTAT=Zero TC
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Figure 1: General Principle of Bandgap Circuits[1]
PTAT+CTAT=Zero TC
Bandgap Circuits
� Bandgap Voltage VREF =VBE +17.2VT
≈1.25V
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T����0 Vref����Eg/q : Bandgap voltage of silicon
Bandgap Reference Circuits
PTAT Current Generation
ln( )Tref
V nI
R=
VREF=VBE3+kVTln(n)
-A Start-up circuit is needed!
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Figure 2: PTAT current generation [3]
refIR
=VREF=VBE3+kVTln(n)
CTAT←
Figure 3: Adding PTAT and CTAT terms
Bandgap Reference Circuits
� CMOS�parasitic bipolar transistors
Figure 4: PNP BJT in CMOS technology [2]
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Figure 4: PNP BJT in CMOS technology [2]
Figure 6:Typical layout of BJTs [3]
Figure 5: Conceptional Layout of BJTs[4]
Bandgap Reference Circuits
[ ] 22
3
ln( ) (1 )out EB T OS
RV V V n V
R= + + +
2(1 )R
V V= +
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2( )
3
(1 )OS out OS
RV V
R= +
How to solve Offset voltage problem-Large Input Devices -R1=mR2����VT ln(mn)
-Double by cascading����VREF doubles����Difficult to realize at low supply voltagesBEV∆
Figure 7: Effect of opamp offset
Bandgap Reference Circuits
� Speed and Noise Issues
Bypass Cap
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Figure 8: Speed Issues [2]
Bandgap Reference Circuits
� Noise
How to decrease noise:-Use small value of resistors(thermal noise)-Minimize number of components
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Figure 9: Effect of noise [2]
Design Examples[1]
Voltage to current Conversion by Switch Cap. Circuits
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Figure 10: VBE referenced bandgap circuit [1]
Figure 11: V-I conversion [2]
Design Examples[2]
Simulation with UMC018 technology
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Figure 12: Designed Bandgap CircuitFigure 13: Change of BG Voltage with
Temperature
Design Examples[3]
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Figure 14: A detailed bandgap circuit [2]
Design Examples[4]
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Figure 15: Low Voltage Bandgap Circuit [5]
Design Examples [4]
Power supply voltage
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Figure 16: Simulation results for low voltage bandgap circuit [6]
Power supply voltage
Design Examples[4]
� Simulation with UMC018 technology
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Figure 17: Simulation result for the designed low voltage BG circuit
Conclusion
� Various kind of bandgap circuits are introduced.
� Their design and simulation results are shown.
� [6] can be used in low voltage applications.
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REFERENCES
� [1] P.R. Gray and R.G. Meyer, Analysis and Design of Integrated
Circuits. New York: John Wiley & Sons, Inc. 1993.
[2] B. Razavi, Design of Analog CMOS Integrated Circuits, McGraw-Hill,
2000.
[3] F. Maloberti, Analog design for CMOS VLSI systems, Kluwer, 2001.
[4] Texas A&M University,
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[4] Texas A&M University,
http://amesp02.tamu.edu/~sanchez/607%20Lect%204%20Bandgap-
2009.pdf
[5] H. Banba, H. Siga, A. Umezawa, T. Miyaba, T. Tanzawa, S. Atsumi, and
K. Sakui, “A CMOS bandgap reference circuit with sub-1-V operation,”
IEEE J. Solid-State Circuits, vol. 34, pp. 670–674, May 1999.
[6] A. Boni, “Op-Amps and Startup Circuits for CMOS Bandgap References
With Near 1-V Supply”, IEEE JOURNAL OF SOLID-STATE CIRCUITS,
VOL. 37, NO. 10, OCTOBER 2002.
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