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Showing posts with label General Amplifiers:. Show all posts
ANALOG ELECTRONIC CIRCUITS × General Amplifiers:
• Main feature of the Darlington connection is that the composite acts as a
single unit with a current gains of individual transistors.
• Darlington connection provides a current gain of βo= β1+ β2
• If β1= β2= β then βo= β2
• This configuration provides a transistor having a very large current gain,
typically a few thousands
ANALOG ELECTRONIC CIRCUITS × General Amplifiers:
• A cascode connection has one transistor on top in series with another.
• Figure below shows CE stage feeding a CB stage.
• This arrangement is designed to provide a high input impedance with low
voltage gain to ensure that the input Miller capacitance is at a minimum with
the CB stage providing good high frequency operation.
ANALOG ELECTRONIC CIRCUITS × General Amplifiers:
• RC coupled cascade amplifier is taken here for example
• Advantage of cascading is increase in the overall voltage gain.
• Dc bias is obtained by procedure followed for single stage amplifier.
• Gain of each stage: AV= -(RC װ RL )/re
• Amplifier input impedance is that of
stage 1: Zi= R1 װ R2 װ βre
• Output impedance is that of stage 2 :
Zo=Rc װ ro
ANALOG ELECTRONIC CIRCUITS × General Amplifiers:
• Cascade connection is a series connection with the output of one stage then
applied as input to the second stage.
• Cascade connection provides a multiplication of the gain of each stage for a
larger overall gain.
• Gain of overall cascade amplifier is the product of stage gains AV1 and AV2
Av = Av1AV2 = (-gmRD1) (-gmRD2)
• The input impedance of the cascade amplifier is that of stage 1,
Zi = RG1
• Output impedance is that of stage 2,
Z0=RD2
• The main function of cascading the stages is the larger overall gain achieved.
