Electronic Circuits EE 359-Lecture 3

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Electronic CircuitsEE 359-Lecture 3

• Prof. Uf Tureli
• Dept. of ECE
• Stevens Institute of Technology

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Course Outline

• Syllabus and announcements
• http//koala.ece.stevens-tech.edu/utureli/EE359
  
• HW 1 due today
• 5th Ed. 2.100,3.18,3.19,3.26
• HW 2 due Friday
• 3.52, 3.72, 3.66 , 3.98

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Small Signal Model

• Small signal, biased operation

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Diode Model

• As a resistor with value equal to reciprocal of
  the slope of the i-v curve
• Linearization around bias point VD and time
  varying signal vd(t) is superimposed.
• Current due to VD
• Approx.

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Small Signal Approximation
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Equivalent circuit model

• For small changes around bias point Q is
  reciprocal of tangent
• VD0 is the intercept of the tangent on the vD
  axis

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Separate DC and small signal analysis
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Practical Diode Circuit

• Diode charges capacitor.
• The diode is assumed ideal. It will only conduct
  when vI is more than vo

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Rectifier

• Voltage and current waveforms in the peak
  rectifier circuit with CR ?? T.
• The diode is assumed ideal.

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Basic Limiting Ckts
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BJT Transistor

• Three terminal device
• Three semiconductor regions, above is pnp
• E Emitter, B Base, C Collector
• Voltage between two terminals to control current
• Use as Amplifier or Switch

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NPN Transistor

• Current flow in an npn transistor biased to
  operate in the active mode
• Forward bias of Emitter-Base Junction current
  flows to emitter, electrons move towards base,
  holes to emitter
• Reverse bias of Base-Collector Junction IC
  independent of VCB

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• Minority carriers in the emitter of npn
  transistor operating in the active mode vBE ? 0
  and vCB ? 0.
• Electron concentration highest at emitter side,
  and lowest at collector side on the p region
  (base in npn transistor)

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Equivalent Circuit

• iC indep of VCE
• Nonlinear voltage controlled source

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Current Controlled Source

• Change voltage controlled source to current
  controlled source

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Simplify Models

• Voltage Controlled Model

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Simplify Current Controlled Source Model

• Transistor as two port network with input B and
  output C.
• Current gain b
• Constant n1 except
• High currents
• Low currents
• Where n2 .

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PNP Transistor

• Current in PNP mainly due to holes injected from
  emitter to base

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Large-signal models

• for the pnp transistor operating in the active
  mode.
• Identical to PNP, replace vBE by vEB

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BJT Characteristics

• iC-vCB characteristics for an npn transistor in
  the active mode.
• Collector is constant current source only
  controlled by emitter current iC

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BJT Characteristics
Conceptual circuit for measuring the iC-vCE
characteristics of the BJT. (b) The iC-vCE
characteristics of a practical BJT.
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Transistor as an amplifier. (b) The circuit of
(a) with the signal source vbe eliminated for dc
(bias) analysis.
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Small Signal Analysis

• Linear operation of the transistor small-signal
• vbe triangular waveform is superimposed on dc
  voltage VBE.
• Collector signal current ic, also of triangular
  waveform, superimposed on the dc current IC.
• Ic gm vbe, where gm is the slope of the ic -
  vBE curve at the bias point Q.

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BJT as Amplifier
BJT as a current-controlled current source (a
current amplifier). 
BJT as a voltage-controlled current source ( a
transconductance amplifier)
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T-MODEL
Emitter resistance re rather than the base
resistance r? featured in the hybrid-? model.
Current-controlled current source representation.
Voltage-controlled current source
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Transistor Amplifier
Example

• NPN

• Quiescent point

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Small Signal Analysis
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Small Signal