Lecture 29 - BJT Non-idealities

Lecture 29 - BJT Non-idealities - BJT Non-idealities...

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1 BJT Non-idealities Objectives: To understand BJT device models and non idealities models and non-idealities. Questions to be answered: • What factors lead to non-ideal BJT behavior? EE360 – Lecture 29 Non-idealities: Base-width Modulation • Depletion widths change with varying biases, and thus the base width changes. • Most significant effect is reverse bias on collector base junction (V CB ) Not strictly a non ideality because our analysis depends From Pierret, pg. 411. EE360 – Lecture 29 Not strictly a non-ideality because our analysis depends on W , the width between the depletion edges, not on W B , the width of the base region.

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2 Non-idealities: Base-width Modulation • In common-emitter configuration base-width modulation leads to an upward slope in I C with increasing V CE . • Setting W = W B : “ideal” I C vs. V EC relationship (left plot). Calculate W based on the applied voltages Calculate B based on the applied voltages: V EC ↑∴ - V CB W ↓∴ I C increases (right plot). pnp transistor in common emitter configuration Ideal Curves ( W = W B ) Real Curves EE360 – Lecture 29 I C vs. V EC From Pierret, pg. 409. Non-idealities: Base-width Modulation The slope in I C vs. V EC is called the Early effect, and the voltage at which the extrapolated lines intersect is called the Early voltage.
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Lecture 29 - BJT Non-idealities - BJT Non-idealities...

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