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Lecture 24 Last time: Small-signal model for the entire common- - - PowerPoint PPT Presentation

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EECS 105 Spring 2002 Lecture 24 R. T. Howe Lecture 24 Last time: Small-signal model for the entire common- source amplifier Limits to model Today : Two-port small-signal models of amplifiers University of California

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SLIDE 1
  • R. T. Howe

EECS 105 Spring 2002 Lecture 24

  • Dept. of EECS

University of California at Berkeley

Lecture 24

  • Last time:

– Small-signal model for the entire common- source amplifier – Limits to model

  • Today :

– Two-port small-signal models of amplifiers

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SLIDE 2
  • R. T. Howe

EECS 105 Spring 2002 Lecture 24

  • Dept. of EECS

University of California at Berkeley

Generalized Amplifier

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SLIDE 3
  • R. T. Howe

EECS 105 Spring 2002 Lecture 24

  • Dept. of EECS

University of California at Berkeley

Amplifier Terminology

Sources: signal, its source resistance, and bias voltage

  • r current

Load: use resistor in Chap. 8, but could be a general impedance Port: a pair of terminals across which a voltage and an associated current are defined source, load: “one port” amplifier: “two port”

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SLIDE 4
  • R. T. Howe

EECS 105 Spring 2002 Lecture 24

  • Dept. of EECS

University of California at Berkeley

Amplifier Biasing

Select VIN(or IIN) to set the DC device current to equal the supply current ISUP. DC output current IOUT = DC output voltage VOUT = Small-signal source voltage or source current results in small-signal device current id

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SLIDE 5
  • R. T. Howe

EECS 105 Spring 2002 Lecture 24

  • Dept. of EECS

University of California at Berkeley

One-Port Models (EECS 40)

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SLIDE 6
  • R. T. Howe

EECS 105 Spring 2002 Lecture 24

  • Dept. of EECS

University of California at Berkeley

Small-Signal Two-Port Models

We assume that input port is linear and that the amplifier is unilateral: The output port : depends linearly on the current and voltage at the input and output ports

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SLIDE 7
  • R. T. Howe

EECS 105 Spring 2002 Lecture 24

  • Dept. of EECS

University of California at Berkeley

Math 54 Perspective

Can write linear system of equations for either iout or vout in terms of two of iin, vin, iout, or vout: possibilities are

  • ut

in

  • ut

v v i

2 1

α α + =

  • ut

in

  • ut

v i i

4 3

α α + =

  • ut

in

  • ut

i v v

6 5

α α + =

  • ut

in

  • ut

i i v

8 7

α α + =

What is physical meaning of α1? of α6?

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SLIDE 8
  • R. T. Howe

EECS 105 Spring 2002 Lecture 24

  • Dept. of EECS

University of California at Berkeley

EE Perspective

Four amplifier types: determined by the output signal and the input signal … both of which we select (usually obvious) Voltage Current Transconductance Transresistance We need methods to find the 6 αi parameters for the four models and equivalent circuits for unilateral two ports

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SLIDE 9
  • R. T. Howe

EECS 105 Spring 2002 Lecture 24

  • Dept. of EECS

University of California at Berkeley

Two-Port Small- Signal Amplifiers

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SLIDE 10
  • R. T. Howe

EECS 105 Spring 2002 Lecture 24

  • Dept. of EECS

University of California at Berkeley

Input Resistance Rin

Looks like a Thevenin resistance measurement, but note that the

  • utput port has the load resistance attached

attached R removed R t t in

L S

i v R

,

=

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SLIDE 11
  • R. T. Howe

EECS 105 Spring 2002 Lecture 24

  • Dept. of EECS

University of California at Berkeley

Output Resistance Rout

Looks like a Thevenin resistance measurement, but note that the input port has the source resistance attached

attached R removed R t t

  • ut

S L

i v R

,

=