chapter 3 small-singal audio-frequency amplifiers

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chapter 3 small-singal audio-frequency amplifiers

• 3.6 draw the fig 1.1 of the assignment.
• 3.7 four terminal
• 3.8 the amplifier technology parameter
• 3.8.1V(PPmax)
• 3.8.2voltage gain and current gain
• 3.8.3input impedance
• 3.8.4ouput impedance
• 3.8.5frequency band
• 3.9 Voltage, current and power amplifiers
• 3.10 Multi-stage amplifiers
• 3.11 Measurements on audio-frequency amplifiers

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4-termianal
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• The h parameters of a transistor are defined by
  considering
• the transistor to be a four-terminal
  network(Fig.1.3).If the
• input current II and the output voltage Vo are
  taken to be the
• independent variables,then the input voltageVI
  and the
• output current IO can be written down as
• VIIIhIVOhR (1.1)
• IO IIhFVOhO (1.2)

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In the common-emitter connection
input impedance
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A.C.Load Lines
Fig. 3.10 A.C.Load Lines
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Current Gain of a Transistor Amplifier
Fig. 3.9 Potential-divider bias amplifier
Fig. 3.11 Current Gain of a Transistor
Amplifier
? When an input signal is applied to a transistor
amplifier, the signal current iS super imposed
upon the bias current. ? suppose that the base
bias current is IB2 and that an input signal
current swings the base current between the
values IB1 and IB3. ? The resulting values of
collector current are found by projecting onto
the collector-current axis from the in tersection
of the a.c.load line and the curves for IB1 and
IB3.
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Current Gain of a Transistor Amplifier
Fig. 3.9 Potential-divider bias amplifier
Fig. 3.11 Current Gain of a Transistor
Amplifier
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example 3.2 The transistor used in the circuit
has the data given in Table. Plot the output
characteristics of the transistor. Draw the dc
load line and select a suitable operating point.
Draw the ac load line and use it to find the
alternating current that flows in the 2500O load
when an input signal producing a base current
swing of15µA about the bias current is applied
to the circuit. Assume all the capacitors have
zero reactance at signal frequencies.
Fig. 3.12 example 3.2
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Voltage Gain of a FET Amplifier
? The voltage gain of a fet can also be found
with the aid of a load line. For example, Fig.
3.13 shows an ac load line drawn on the drain
characteristics of a fet and the dotted
projections from the load line show how the drain
voltage swing, resulting from the application of
an input signal voltage, can be found.The voltage
gain Av of the fet amplifier stage is
Fig. 3.13 Potential-divider bias amplifier
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3.8.1V(PPmax)
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rbe
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rbe
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3.8.2voltage gain and current gain
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3.8.3input/output impedance
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3.8.4frequency band
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3.9 Voltage, current and power amplifiers (P47)
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3.10 multi-stage amplifier
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3.11 Measurements on audio-frequency amplifiers
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