ENEE 303 1st Discussion

Self-Introduction Name: Yusen Fan Email: ysfan@umd.edu Office Hour: Tuesdays 10-12 @ AVW 1143

Contents Pspice demonstration Diode, BJT overview

Pspice Tutorial: https://engineering.purdue.edu/~ee255/lecturesupp_files/PSpice-Tutorial.pdf

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

Bipolar Junction Transistors Diode Bipolar Junction Transistors ENEE 303 Fall 2016

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

Example 4.2: Multiple Diodes

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.

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.

Bipolar Junction Transistors BJT Bipolar Junction Transistors ENEE 303 Fall 2016

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)

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

iC – vBE Characteristic for an npn Transistor

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

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

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