This document summarizes a presentation on voltage reference sources. It introduces voltage references and their requirements of precision, stability, and independence from various factors. It describes the I-V characteristics of ideal references and defines sensitivity. It then outlines different types of voltage references such as voltage dividers, MOS diode references, and band-gap references. Applications like ADCs are discussed. In conclusion, it emphasizes that voltage references must provide accurate, constant voltages independently of operating conditions.

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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