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 is a measure of dependence of Vref

(Iref) upon a parameter or variable x which influences Vref (Iref).

x

V

vx

xx

V

V

ref

ref

ref

refV

xSref

xx

V

VSrefV

xref

ref

;

Where x could be VDD or temperature

SENSITIVITY

Minimize the fractional Temperature Coefficient

TEMPERATURE DEPENDANCE

BOOTSTRAPPED CURRENT SOURCE

51BE

2 IR

VI

BE2 VRIV

VBE REFERENCE CURRENT SOURCE

Simple Voltage References

Objective is to minimize

Sref

DD

V

V

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