1. ENEE 303 1st Discussion

2. Self-Introduction Name: Yusen Fan
Office Hour: Tuesdays AVW 1143

3. Contents
Pspice demonstration
Diode, BJT overview

4. Pspice
Tutorial:

5. Pspice diode and transistor models
Can be found on the course website
e.g.
PSpice diode model for 1N4007
PSpice models for BJT 2N390x transistors

6. Bipolar Junction Transistors
Diode
Bipolar Junction Transistors
ENEE 303 Fall 2016

7. Current-Voltage Relationship of a pn-Junction
𝐼= 𝐼 𝑆 𝑒 𝑉 𝑉 𝑇 −1
𝐼 𝑆 =𝐴𝑞 𝑛 𝑖 2 𝐷 𝑝 𝐿 𝑃 𝑁 𝐷 + 𝐷 𝑛 𝐿 𝑛 𝑁 𝐴
Ideal model

8. Example 4.2: Multiple Diodes

9. Small-Signal Model Q: How is small-signal resistance rd defined?
(Slope at the Q point)
A: From steady-state current (ID) and thermal voltage (VT) as below.
Note this approximation is only valid for small-signal voltages vd < 5mV.

10. Small-Signal Model
Consider the circuit shown above for the case in which R = 10kOhm.
The power supply V+ has a dc value of 10V over which is super-imposed a 60Hz sinusoid of 1V peak amplitude (known as the supply ripple)
Q: Calculate both amplitude of the sine-wave signal observed across the diode.
A: vd.(peak) = 2.68mV
Assume diode to have 0.7V drop at 1mA current.

11. Bipolar Junction Transistors
BJT
Bipolar Junction Transistors
ENEE 303 Fall 2016

13. Common-Emitter Current Gain 𝜷
𝛽= 𝑖 𝐶 𝑖 𝐵
common-emitter current gain (b.) – is influenced by two factors:
width of base region (W)
relative doping of base emitter regions (NA/ND)
High Value of b
thin base (small W in nano-meters)
lightly doped base / heavily doped emitter (small NA/ND)

14. Common-Base Current Gain 𝒂
All current which enters transistor must leave.
𝑖 𝐸 = 𝑖 𝐶 + 𝑖 𝐵
When combined with equations from the previous slides
𝑖 𝐸 = 𝑖 𝐶 + 𝑖 𝐶 𝛽 = 𝛽+1 𝛽 𝑖 𝐶 = 𝛽+1 𝛽 𝐼 𝑆 𝑒 𝑣 𝐵𝐸 𝑉 𝑇
𝑖 𝐶 =𝛼 𝑖 𝐸
𝛼= 𝛽 𝛽+1

15. iC – vBE Characteristic for an npn Transistor

16. Operation regions of BJT
Active mode: BE forward biased, CB reverse biased
2. Saturation mode:
BE, CB are both forward biased
3. Cut off mode:
BE, CB reverse biased

17. Models for the Operation of the
npn BJT in Various Modes
npn transistor
cutoff mode
saturation mode
active mode

18. Example 6.3 a) Find VBB to achieve, active mode with VCE = 5 V
Assume VBE = 0.7 V and b = 50.