6.8. DESIGN PROBLEMS 301
6.8 DESIGN PROBLEMS ...............................
Problem 6.1Consider anpnSi-BJT at 300 K with the following parameters:
Nde =10^18 cm−^3
Nab =10^17 cm−^3
Ndc =10^16 cm−^3
Db =30.0cm^2 s−^1
Lb =10. 0 μm
Wb =1. 0 μm
De =10cm^2 s−^1
Le =5. 0 μm
electron mobility in the emitter = 500 cm^2 V−^1 s−^1
area = 5. 0 × 10 −^7 cm^2
Calculate the emitter efficiency and gainβwhen the EBJ is forward biased at 1.0 V and
the BCJ is reverse biased at (a): 5.0 V and (b) 10.0 V.
For high-speed operation, it is found that the BJT discussed above has too large an emitter
resistance. The device designer wants to limit the emitter resistance (keeping the area
unchanged) to 2.0Ω. Calculate the emitter efficiency andβfor the new device using the
case (a) given above.
Problem 6.2Consider anpnSi-BJT at 300 K with the following parameters:
Nde =10^18 cm−^3
Nab =10^17 cm−^3
Ndc =5× 1016 cm−^3
Db =30.0cm^2 s−^1
Lb =15. 0 μm
De =10.0cm^2 s−^1
Le =5. 0 μm
Design the maximum base width,Wb, that will allow a current gainβof 100 when the
EBJ is forward biased at 1.0 V and the BCJ is reverse biased at 5.0 V. You may make the
following approximations:
- The reverse bias collector current is zero.
- Wbis much smaller thanLb.
