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REFERENCE CIRCUITS
A Reference Circuit is an independent voltage or
current source which has a high degree of precision
and stability.
Requirements of a Reference Circuit
1. Output voltage/current should be independent of
Power Supply
2. Output voltage/current should be independent of
temperature
3. Output voltage/current should be independent of
process variations.
SENSITIVITY
Sensitivity is a measure of dependence of Vref (Iref)
upon a parameter or variable x which influences Vref
(Iref).
Vref
Vref
Vref
x Vref ;
S  x  v
ref x
x
x
Vref
Vref
x
 S
Vref
x x
Where x could be VDD or temperature
TEMPERATURE DEPENDANCE
Minimize the fractional Temperature Coefficient
BOOTSTRAPPED CURRENT SOURCE
VBE REFERENCE CURRENT SOURCE
I2 
VBE1
R
 I5
V  I2R  VBE
Simple Voltage References
Objective is to minimize
Vref
S
VDD
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
ACTIVE VOLTAGE DIVIDERS
PN JUNCTION VOLTAGE REFERENCE
VBE MULTIPLIER
PN JUNCTION
GATE SOURCE REFERENCE CIRCUIT
GATE SOURCE VOLTAGE FOR CONSTANT
CURRENT (STRONG INVERSION)
GATE SOURCE REFERENCE CIRCUIT
BANDGAP VOLTAGE REFERENCE
By taking the derivative at T0 (assuming that JC has
a temperature dependence of Tα , the dependence of
VBE with temperature is given by
CURVATURE CORRECTION ?
CORRECTION TOPOLOGY