Lecture19-MOS+Capacitors - ECE 3040: Microelectronic...

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ECE 3040 - Dr. Ying Zhang Georgia Tech ECE 3040: Microelectronic Circuits Lecture 19 Reading: Pierret 16.2, 16.3, 17.1, 17.2
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ECE 3040 - Dr. Ying Zhang Georgia Tech Diffusion capacitance: m F T C F B po Q BE C B po Q BE B B g V I C v i D W v Q C ττ = = = = int 2 int 2 Recapture BJT Base Charging Capacitance (Diffusion Capacitance) base emitter for bi EB jEo jE V V C C + = 1 Depletion capacitance: jE B C C C + = π Total emitter-base capacitance is:
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ECE 3040 - Dr. Ying Zhang Georgia Tech Depletion capacitance of the collector-base junction junction C B the for voltage in built V ce capaci depletion bias zero C where V V C C base collector for bi o base collector for bi CB o + = tan , 1 μ Recapture Depletion Capacitance of the C-B Junction and C-S Junction Depletion capacitance of the collector-substrate junction junction substrate C the for voltage in built V ce capaci depletion bias zero C where V V C C substrate collector for bi CS substrate collector for bi CS CS CS + = tan , 1
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ECE 3040 - Dr. Ying Zhang Georgia Tech Recapture Complete Small Signal Model of the BJT
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ECE 3040 - Dr. Ying Zhang Georgia Tech Recapture When to use which Model Ebers-Moll model: Always valid! Cutoff, saturation, forward active (active) and reverse active (inverse) β Analysis (assume a turn on voltage when given β ): Forward active DC solution only. Note: β only has meaning in forward active mode! Small Signal Models (y-parameter, hybrid- π , etc…) Forward active mode solving for the small signal (AC) solution only
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ECE 3040 - Dr. Ying Zhang Georgia Tech Recapture: Single Transistor Amplifier Analysis 1.) Determine DC operating point and calculate small signal parameters (see next page) 2.) Convert to the AC only model. DC Voltage sources are shorts to ground DC Current sources are open circuits Large capacitors are short circuits Large inductors are open circuits 3.) Use a Thevenin circuit (sometimes a Norton) where necessary. Ideally the base should be a single resistor + a single source. Do not confuse this with the DC Thevenin you did in step 1. 4.) Replace transistor with small signal model 5.) Simplify the circuit as much as necessary. Steps to Analyze a Transistor Amplifier Step 2 Step 3 Step 4 Step 5 Step 1 Important! 6.) Calculate the small signal parameters (r π , g m , r o etc…) and then gains etc…
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ECE 3040 - Dr. Ying Zhang Georgia Tech Recapture Understanding a BJT Circuit I B Direction of Current Symbol Key Increasing Voltage Increasing Current Decreasing Voltage Decreasing Current I E I C V B V E V C Conclusion: V E will “follow” V B (as V B increases so does V E ) V C will take the inverse action of V B (as V B increases V C will decrease).
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ECE 3040 - Dr. Ying Zhang Georgia Tech ± MOS Capacitor ± MOS Capacitor Electrostatics ± Gate Voltage Relationship Agenda
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ECE 3040 - Dr. Ying Zhang Georgia Tech MOS Capacitor Metal “Gate”
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This note was uploaded on 09/05/2009 for the course ECE 3040 taught by Professor Hamblen during the Spring '07 term at Georgia Institute of Technology.

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Lecture19-MOS+Capacitors - ECE 3040: Microelectronic...

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