EE 434 Lecture 22. Properties of Bipolar Devices

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1 EE 434 Lecture 22 Properties of Bipolar Devices

2 Quiz 16 A dc current source is shown. If the device has width W50u, lenth L1.2u, ucox100ua -2, T.75 and.04-1, determine a) The nominal output current b) The small sinal output impedance c) The minimum output voltae to maintain operation as a current source

3 1 And the number is

4 Quiz 16 Solution A dc current source is shown. If the device has width W50u, lenth L1.2u, ucox100ua -2, T.75 and.04-1, determine a) The nominal output current b) The small sinal output impedance c) The minimum output voltae to maintain operation as a current source I I C DQ OX W 2L ( ) 2 EB 2 ( ) ma 3.25mA 4 DQ 10

5 Quiz 16 Solution A dc current source is shown. If the device has width W50u, lenth L1.2u, ucox100ua -2, T.75 and.04-1, determine a) The nominal output current b) The small sinal output impedance c) The minimum output voltae to maintain operation as a current source I I C DQ OX W 2L ( ) 2 EB 2 ( ) ma 3.25mA 4 DQ 10

6 Quiz 16 Solution A dc current source is shown. If the device has width W50u, lenth L1.2u, ucox100ua -2, T.75 and.04-1, determine a) The nominal output current b) The small sinal output impedance c) The minimum output voltae to maintain operation as a current source R R OUT OUT 1 o KΩ 1 λ I.04v 3.25mA DQ

7 Quiz 16 Solution A dc current source is shown. If the device has width W50u, lenth L1.2u, ucox100ua -2, T.75 and.04-1, determine a) The nominal output current b) The small sinal output impedance c) The minimum output voltae to maintain operation as a current source To maintain saturation reion operation, DS > GS - T OUT >

8 Review from Last Time Alternate equivalent small sinal model for BJT includes current dependent current source as alternative to transconductance source For a bipolar transistor >> >> m o m for the BJT is much larer than that of the MOSFET (ood) for BJT is much larer than that of the MOSFET (not so ood)

9 Other Properties of BJT Alternate Equivalent Small Sinal Model Relative manitude of small sinal parameters Simplified small sinal model Comparison of BJT and MOSFET

10 Comparison of MOSFET and BJT BJT MOSFET Assume BJT operatin in FA reion, MOSFET operatin in Saturation Assume same quiescent output voltae and same resistor R 1 One of the most widely used amplifier architectures

11 Comparison of MOSFET and BJT BJT MOSFET Assume BJT operatin in FA reion, MOSFET operatin in Saturation Assume same bias current One of the most widely used amplifier architectures in interated applications Special Case of Previous Architecture

12 Comparison of MOSFET and BJT BJT MOSFET

13 Comparison of MOSFET and BJT BJT MOSFET

14 Comparison of MOSFET and BJT BJT G 1 R 1 1 v OUT o m + G 1 v IN A v v OUT IN m 0 + G 1 v A OUT OUT IN G m 1 v IN mr 1 m I CQ t A I CQ t R 1

15 Comparison of MOSFET and BJT MOSFET G 1 R 1 1 v OUT o m + G 1 v IN A v v OUT IN m 0 + G 1 v A OUT G OUT IN m 1 v IN mr 1 m 2I DQ EB A 2I DQ EB R 1

16 Comparison of MOSFET and BJT BJT MOSFET 2I ICQR DQ 1 1 AB AM t EB AB EB AM 2 t A B is typically much larer than A M for this basic amplifier architecture R

17 Comparison of MOSFET and BJT BJT MOSFET Assume same bias currents

18 Comparison of MOSFET and BJT BJT MOSFET A v v OUT IN Identical functional form Assumin same bias currents m 0 A A B M A A B M mb ob mm om mb mm om ob A v v OUT Typically A B >>A M EB [ λaf ] 2 t IN m 0

19 Comparison of MOSFET and BJT How do the areas required for implementin a MOSFET compare to those required for a BJT To make the comparison fair, will assume the same lithoraphy equipment and that the minimum feature size both processes is 2 Refer the desin rules for a bipolar process in the GAS text if additional details are needed The followin slides are adapted from the BJT technoloy presentation

20 1 mid-line of isolation λ Emitter diffusion base diffusion λ 12λ 2λ 2λ 6λ 3λ 2λ 14λ 62λ burried collector Note: 24λ required Between p-base and isolation diffusion n-epi Minimum spacins for BJT (top view) Isolation diffusion

21 1 mid-line of isolation Emitter diffusion 67λ base diffusion 62λ burried collector Note: Not to vertical Scale Boundin Area 4154λ n-epi Isolation diffusion

1 1 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 5 10 15 Minimum-Sized

22 Minimum-Sized MOSFET 20 14λ λ Boundin Area 168λ 2 Active Area 6λ

1 1 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 5 10 15 20 25

23 λ 62λ MOSFET BJT Note: Not to vertical Scale

24 Other Properties of BJT Alternate Equivalent Small Sinal Model Relative manitude of small sinal parameters Simplified small sinal model Comparison of BJT and MOSFET Equivalent Circuit for dc biasin

25 Bipolar Models Simple dc Model Small Sinal Model Better Analytical dc Models Sophisticated Model for Computer Simulations Frequency-Dependent Small Sinal Model Better Models for Predictin Device Operation

26 Bipolar Models Simple dc Model for Biasin I B J S A E e BE t I β C I B I J C I S A β E e C I B BE t Althouh it may appear this is a model simplification, it is still hihly nonlinear because the diode from BE is nonlinear

27 Recall Transfer Characteristics J S.25fA/u 2 A E 400u BE I C (ma) BE close to 0.6 for a two decade chane in I C around 1mA

28 Bipolar Models Simple dc Model for Biasin I B JSA E e BE t I β C I B I β C I B BE is approximately 0.6 when in FA reion

29 Bipolar Models Simple dc Model for Biasin JSA I B I β E e C I B BE t I β C I B BE is approximately 0.6 when in FA reion BE 0.6 I β C I B I β C I B Dramatic Simplification in Model Widely used for biasin

30 Bipolar Models Simple dc Model for Biasin BE 0.6 I β C I B I β C I B When is this model justifiable? When it doesn t make much difference in the analysis of a circuit whether BE 0.6 or 0.7 When the CE dependence on the collector current is neliable

EE 330 Lecture 21. Bipolar Process Flow

EE 330 Lecture 21. Bipolar Process Flow EE 330 Lecture 21 Bipolar Process Flow Exam 2 Friday March 9 Exam 3 Friday April 13 Review from Last Lecture Simplified Multi-Region Model I C βi B JSA IB β V 1 V E e V CE BE V t AF V BE >0.4V V BC