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
02-07-2012 M. S. Ramaiah School of Advanced Studies 1
2. Contents
• Introduction
• I-V curve for reference sources
• Properties
• Sensitivity
• Types of voltage reference sources
• Applications
• Conclusion
• References
02-07-2012 M. S. Ramaiah School of Advanced Studies 2
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
02-07-2012 M. S. Ramaiah School of Advanced Studies 3
4. I-V curves for ideal references
Figure 2. I-V curves for ideal references [Kumar 2009]
02-07-2012 M. S. Ramaiah School of Advanced Studies 4
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
02-07-2012 M. S. Ramaiah School of Advanced Studies 5
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
02-07-2012 M. S. Ramaiah School of Advanced Studies 6
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]
02-07-2012 M. S. Ramaiah School of Advanced Studies 7
8. Voltage references using voltage division
Figure 5. Voltage references using voltage division [Allen 2009]
02-07-2012 M. S. Ramaiah School of Advanced Studies 8
9. MOSFET – Resistance Voltage references
Figure 6. MOSFET – Resistance Voltage references [Allen 2009]
02-07-2012 M. S. Ramaiah School of Advanced Studies 9
10. Simulation waveforms
Figure 4. Simulation waveforms for MOSFET – Resistance reference sources
02-07-2012 M. S. Ramaiah School of Advanced Studies 10
11. Applications
• Error amplifier,
• Comparator,
• A/D and D/A converters
Figure 7. Typical use of a voltage reference for an ADC [Whelan 2009]
02-07-2012 M. S. Ramaiah School of Advanced Studies 11
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.
02-07-2012 M. S. Ramaiah School of Advanced Studies 12
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
02-07-2012 2012] M. S. Ramaiah School of Advanced Studies 13
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
02-07-2012 M. S. Ramaiah School of Advanced Studies 15
Notes de l'éditeur
Goal is to minimize sensitivity to temperature, process n voltage Definition: The fractional change in the reference voltage is equal to the sensitivity times the fractional change in the power supply voltage. For example, if the sensitivity is 1, then a 10% change in VDD will cause a 10% change in VREF.
The voltage divider formed with two resistors has the advantage of simplicity, temperature insensitivity and process variations but the main problem with this circuit is that in order to reduce the power dissipation (i.e., the current through the resistors), the resistors must be made large. Since large resistors require a large area on the die, this voltage divider may not be practical in many cases. One situation where we will use this simple voltage divider is in generating a voltage halfway between VDD and ground, VDDI2, (sometimes called the common-mode voltage of an analog circuit or system). The voltage divider formed between the resistor and the MOSFET can be recognized as the same circuit used for a bias in the current mirror The final reference, a voltage divider between NMOS and PMOS devices, has the advantage that the layout can be small
![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
02-07-2012 M. S. Ramaiah School of Advanced Studies 1](https://image.slidesharecdn.com/voltagereference-120702113538-phpapp01/85/Voltage-Reference-1-320.jpg)
