1. http://www.eet.bme.hu Budapest University of Technology and Economics Department of Electron Devices Microelectronics, BSc course Bipolar transistors 3 http://www.eet.bme.hu/~poppe/miel/en/08-bipolar3.pptx

2. Budapest University of Technology and Economics Department of Electron Devices 16-10-2014 Microelectronics BSc course, Bipolar transistors 3 © András Poppe & Vladimír Székely, BME-EET 2008-2014 2 Characteristics of the ideal BJT

3. Budapest University of Technology and Economics Department of Electron Devices 16-10-2014 Microelectronics BSc course, Bipolar transistors 3 © András Poppe & Vladimír Székely, BME-EET 2008-2014 3 Common base setup Also called grounded base setup input output

4. Budapest University of Technology and Economics Department of Electron Devices 16-10-2014 Microelectronics BSc course, Bipolar transistors 3 © András Poppe & Vladimír Székely, BME-EET 2008-2014 4 Common base setup Input characteristic: Output characteristic: IEIE normal active saturation closed normal active closed inverse active saturation inputoutput

5. Budapest University of Technology and Economics Department of Electron Devices 16-10-2014 Microelectronics BSc course, Bipolar transistors 3 © András Poppe & Vladimír Székely, BME-EET 2008-2014 5 The process of amplification common base setup in out

6. Budapest University of Technology and Economics Department of Electron Devices 16-10-2014 Microelectronics BSc course, Bipolar transistors 3 © András Poppe & Vladimír Székely, BME-EET 2008-2014 6 Common emitter setup Also called as grounded emitter setup

7. Budapest University of Technology and Economics Department of Electron Devices 16-10-2014 Microelectronics BSc course, Bipolar transistors 3 © András Poppe & Vladimír Székely, BME-EET 2008-2014 7 Common emitter setup B : common emitter, large signal current gain

8. Budapest University of Technology and Economics Department of Electron Devices 16-10-2014 Microelectronics BSc course, Bipolar transistors 3 © András Poppe & Vladimír Székely, BME-EET 2008-2014 8 Common emitter setup No current flows. Part of the base current is spent on accumulating the base chrage. U BE voltage increases, the emitter current starts to flow. The other part of the base current is spent on recombination with some part of the emitter current. The charge in the base is not increased any longer. Any increase of the base current recombines with a given part of the emitter current, thus, the emitter current will also increase. charge increases charge is constant is constant increasing

9. Budapest University of Technology and Economics Department of Electron Devices 16-10-2014 Microelectronics BSc course, Bipolar transistors 3 © András Poppe & Vladimír Székely, BME-EET 2008-2014 9 Common emitter setup Input characteristic: Output characteristic: normal active saturation closed inverse active saturation normal active

10. Budapest University of Technology and Economics Department of Electron Devices 16-10-2014 Microelectronics BSc course, Bipolar transistors 3 © András Poppe & Vladimír Székely, BME-EET 2008-2014 10 X U CE normal active saturation closed inverse active saturation Threshold of saturation: U BC = 0 U BE = U CE normal active

11. Budapest University of Technology and Economics Department of Electron Devices 16-10-2014 Microelectronics BSc course, Bipolar transistors 3 © András Poppe & Vladimír Székely, BME-EET 2008-2014 11 Characteristics of real BJTs: secondary effects ► Parasitic CB diode ► Series resistances ► Early effect ► Operating point dependence of the gain

12. Budapest University of Technology and Economics Department of Electron Devices 16-10-2014 Microelectronics BSc course, Bipolar transistors 3 © András Poppe & Vladimír Székely, BME-EET 2008-2014 12 Effect of the parasitic CB diode No emitter region opposite to it, thus, in inverse oparation the electrons injected from the collector into the base will be lost: inverse active current gain is worsened. inner transistor parasitic junction

13. Budapest University of Technology and Economics Department of Electron Devices 16-10-2014 Microelectronics BSc course, Bipolar transistors 3 © András Poppe & Vladimír Székely, BME-EET 2008-2014 13 Effect of series resistances Base contact E C Where is it exactly? R BB' The "inner base" – good approximation: R BB' B' B

14. Budapest University of Technology and Economics Department of Electron Devices 16-10-2014 Microelectronics BSc course, Bipolar transistors 3 © András Poppe & Vladimír Székely, BME-EET 2008-2014 14 Effect of series resistances Collector contact I C  R CC' adds to U CE  characteristics can be only on the right hand side of the 1/R CC' line reduction of R CC' in case of discrete transistors: epitaxial structure (like in case of diodes) n + emitter p base collector chip carrier (collector lead)

15. Budapest University of Technology and Economics Department of Electron Devices 16-10-2014 Microelectronics BSc course, Bipolar transistors 3 © András Poppe & Vladimír Székely, BME-EET 2008-2014 15 The Early effect Backlash: The output voltage influences the input characteristic

16. Budapest University of Technology and Economics Department of Electron Devices 16-10-2014 Microelectronics BSc course, Bipolar transistors 3 © András Poppe & Vladimír Székely, BME-EET 2008-2014 16 The Early effect

17. Budapest University of Technology and Economics Department of Electron Devices 16-10-2014 Microelectronics BSc course, Bipolar transistors 3 © András Poppe & Vladimír Székely, BME-EET 2008-2014 17 The Early effect The Early voltage out

18. Budapest University of Technology and Economics Department of Electron Devices 16-10-2014 Microelectronics BSc course, Bipolar transistors 3 © András Poppe & Vladimír Székely, BME-EET 2008-2014 18 Early effect at common base setup

19. Budapest University of Technology and Economics Department of Electron Devices 16-10-2014 Microelectronics BSc course, Bipolar transistors 3 © András Poppe & Vladimír Székely, BME-EET 2008-2014 19 Early effect: the backlash ~exp(U BE /U T ) CB setup CE setup

20. Budapest University of Technology and Economics Department of Electron Devices 16-10-2014 Microelectronics BSc course, Bipolar transistors 3 © András Poppe & Vladimír Székely, BME-EET 2008-2014 20 The Early effect Problem What is the output resistance of the transistor in common emitter setup is the Early voltage is 80V and the collector current in the operating point is 5mA? out

21. Budapest University of Technology and Economics Department of Electron Devices 16-10-2014 Microelectronics BSc course, Bipolar transistors 3 © András Poppe & Vladimír Székely, BME-EET 2008-2014 21 Op.p. dependence of current gain Voltage dependence: due to the Early effect

22. Budapest University of Technology and Economics Department of Electron Devices 16-10-2014 Microelectronics BSc course, Bipolar transistors 3 © András Poppe & Vladimír Székely, BME-EET 2008-2014 22 Op.p. dependence of current gain Voltage dependence: due to the Early effect Current dependence: high level