Reference Generators Part II Chapter 4 from Gray and Meyers book - PowerPoint PPT Presentation

2 Reference Generators – Part II Chapter 4 from Gray and Meyer’s book Chapter 11 from Razavi’s book IIT-Bombay Lecture 36 M. Shojaei Baghini

3 Slides Figures • Unless it’s mentioned figures and contents of slides are taken from: ‘Design of Analog CMOS Integrated Circuits’ by Behzad Razavi IIT-Bombay Lecture 36 M. Shojaei Baghini

4 Temperature Variation Tolerant V ref - Negative Temperature Coefficient − V E BE g = ∝ µ × × ∝ µ ∝ µ − < < − V 2 3 m , , kT , 2 1 I I e I kT n n T e T where m T c s s i i 0   ∂ E ( ) V V I V   ⇒ = − + − g BE T C T ln 4 m V   ∂ T 2   T T I T kT S E ( ) − + − g V 4 m V ∂ BE T V q ⇒ = BE ∂ T T E ( ) = = − = g Example room temperatu re : V 0 . 7 V , m 1 . 5 , 1 . 2 V BE q ∂ − − V 0 . 7 0 . 0625 1 . 2 ⇒ = = −  BE 2 mV / K ∂ T 273 IIT-Bombay Lecture 36 M. Shojaei Baghini

5 Temperature Variation Tolerant Biasing- Positive Temperature Coefficient   I   = c 1 Q 1 ( BJT ) : V V ln   BE 1 T   I s 1   I   = c 2 Q 2 ( BJT ) : V V ln   BE 2 T   I s 2 ( ) = = ⇒ − = If I I , I nI V V V ln n c 1 c 2 s 1 s 2 BE 1 BE 2 T ( ) ∂ − ( ) ( ) V V KT ⇒ = = BE 1 BE 2 V ln n ln n ∂ T T q IIT-Bombay Lecture 36 M. Shojaei Baghini

6 Temperature Variation Tolerant Biasing using V BE and V T − ∂ ∂ / V T = + = BE If V V aV with a ∂ ∂ ref BE T V / T T ∂ ∂ = then V / T 0 Silicon bandgap ref Question : Any temper ature? voltage? Example (room temperatu re) : ( ) − = × × × = - 23 19 V 1.38 10 300 / 1 . 602 e 25 . 8 mV T V ∂ ∂ = =  T V / T 0 . 086 mV/ K T T ∂ ∂ = − ⇒ = ⇒ =  V / T 2 m V/ K a 23 . 26 V 1 . 2 V BE ref = a 23.26 is too high for ln(n)! IIT-Bombay Lecture 36 M. Shojaei Baghini

7 Temperature Variation Tolerant Biasing using V BE and V T - Simple Circuit You may redraw I the op-amp I vertically to get a better idea of the structure. ( ) V ln( n ) = + + T V V R R out BE 2 3 2 R 3 IIT-Bombay Lecture 36 M. Shojaei Baghini

8 Effect of Variation of the Current with Temperature     ∂ ∂ ∂ I 1 I 1 I V V     = + − BE T C C S ln V     ∂ ∂ ∂ T     T T I I T I T S C S ∂ I V ln( n ) I = = C T C ∂ T R T T 3   ∂ E V V I ( ) V   ⇒ = − + − g BE T C T ln 3 m V   ∂ T 2   T T I T kT S E ( ) − + − g V 3 m V BE T q Slight change = T IIT-Bombay Lecture 36 M. Shojaei Baghini