1. Voltage Reference Sources
Shankardas Deepti Bharat
CGB0911002
VSD 537
M.Sc. [Engg.] in VLSI System Design
Module Title: Analog and mixed signal circuit design
Module Leader: Mr. Chandramohan P.
Date: 2nd July 2012
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2. Contents
• Introduction
• I-V curve for reference sources
• Properties
• Sensitivity
• Types of voltage reference sources
• Applications
• Conclusion
• References
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3. Introduction
A Reference Circuit is an independent voltage or current source which
has a high degree of precision and stability
Requirements of a Reference Circuit
•Should be independent of power supply
•Should be independent of temperature
Figure 1. Nominal values of a
•Should be independent of processing variations
reference source [Whelan 2009]
•Should be independent of noise and other interference
•Low area
•Easy to Design
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4. I-V curves for ideal references
Figure 2. I-V curves for ideal references [Kumar 2009]
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5. Sensitivity
•Sensitivity is a measure of dependence of Vref upon a
parameter or variable x which influences Vref
∂Vref
Vref
Vref
Vref x ∂Vref ∂Vref ∂x
S = ∂x = vref ∂x = S
x Vref x x
x
Where x could be VDD or temperature
VREF
Ideally, we want S to be zero
V DD
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6. Types of voltage references
1. Voltage Dividers – Active
2. MOS Diode Reference
3. PN Junction Diode Reference
4. Gate-Source Threshold Voltage Reference
5. Base-Emitter Reference Circuit
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7. Types of references (…Continued)
• Reference voltages can be driven from the power supplies using the
resistor and the MOSFET
1 2
3 4
Figure 3. Circuit diagrams of MOSFET – Resistance reference sources [Kumar 2009]
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8. Voltage references using voltage division
Figure 5. Voltage references using voltage division [Allen 2009]
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9. MOSFET – Resistance Voltage references
Figure 6. MOSFET – Resistance Voltage references [Allen 2009]
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10. Simulation waveforms
Figure 4. Simulation waveforms for MOSFET – Resistance reference sources
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11. Applications
• Error amplifier,
• Comparator,
• A/D and D/A converters
Figure 7. Typical use of a voltage reference for an ADC [Whelan 2009]
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12. Conclusion
• Voltage reference is used to establish absolute measurement accuracy.
• Any reference error undermines the overall system accuracy.
• Thus the external voltage reference must provide accurately set
constant voltage, independent of load changes, temperature, input
supply voltage and time.
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13. References
• Brendan Whelan (2009) How to Choose a Voltage Reference [online]
available from <http://cds.linear.com/docs/LT%20Journal/LTMag
-V19N1-03-References-BrendanWhelan.pdf> [01st July 2012]
• Jacob Baker, R. (2010) CMOS: Circuit Design, Layout and Simulation.
3rd edn. Wiley-IEEE
• Phillip E. Allen., and Douglas R, Holberg. (2002) CMOS Analog
Circuit
Design. 2nd edn. Oxford University Press
• Sougata Kumar (2009) Current Reference and Voltage Reference
[online] availabale from <http://conf05.iitkgp.ac.in/avlsi/logf/
summercourse/ 2008/Current_Voltage_reference.pdf> [01st July
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14. Thank You
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15. Remarks
Sl. No. Topic Max. marks Marks
obtained
1 Quality of slides 5
2 Clarity of subject 5
3 Presentation 5
4 Effort and question handling 5
Total 20
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