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发表于 2009-2-12 08:12:40
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The formulation of meaningful analytical procedures and design strategies
for even the most advanced of electronic feedback circuits and systems
relies on a thorough grasp of basic circuit and system concepts. Aside from
abilities to apply and interpret the Kirchhoff voltage and current laws (KVL
and KCL) in both the time and frequency domains, at least three issues
underpin the mission of acquiring design-oriented analytical proficiency in
the electronic circuits arena. The first of these is the theorems attributed to
Thévenin andNorton. An ability to apply these theorems to the problems of
exploring and understanding the electrical dynamics of electronic networks
that couple specified signal sources to an arbitrary linear or nonlinear load
is a virtual cornerstone of the electronic networks discipline. For example,
Thévenin’s and Norton’s theorems might be gainfully applied to deduce
the desired input/output (I /O) electrical characteristics of a preamplifier
designed for insertion between the output terminals of a compact disc player
and the input terminals of the power amplifier used to drive the audio
speakers of a stereo system.
Asecond issue embraces transfer functions of linear networks. The capability
of deducing the transfer characteristic and casting it into appropriate
mathematical form serve a multitude of purposes. Included among these
purposes are a delineation of the input to output gain of the network undergoing
investigation, the determination of the network input and output
impedances, an assessment of the relative stability of the system, and the
determination of the time domain response of the subject circuit to specified
transient and steady state input excitations. Phasor analyses in the sinusoidal
steady state, which is fundamental to a stipulation of the manner in which
the system gain and pertinent impedance levels depend on the frequency of
the applied input signal, are intimately linked to network transfer functions.
Phasors comprise the basis for deducing such electronic circuits and systems
performance metrics as bandwidth, impedances, frequency response,
and phase response. The bandwidth defines the frequency interval over
which the I /O gain is maintained nominally constant. The impedance levels
at the input and output terminals of an active network are instrumental
in determining whether an amplifier is more suitable for voltage than for
current amplification. The frequency response is essentially a mathematical
snapshot of the manner in which the network under consideration performs
over specified intervals of signal frequency. Finally, the phase response
establishes the network delay, which defines the average time required by
a system to process and ultimately deliver the desired steady state output
response to a specified input signal.
The third issue is the intelligent use of the four types of dependent
generators; namely, the voltage controlled current source (VCCS), the
voltage controlled voltage source (VCVS), the current controlled current
source (CCCS), and the current controlled voltage source (CCVS). Understanding
the volt-ampere properties of these mathematical circuit branch
elements is a prerequisite to formulating reasonably accurate, designoriented,
linearized circuit models for active devices, such as the metaloxide-
semiconductor field-effect transistor (MOSFET), the bipolar junction
transistor (BJT), and the PN junction diode. Moreover, exploiting these
properties prudently and creatively is fundamental to the intelligent application
of Thévenin’s and Norton’s theorems and to the efficient deduction
of the transfer characteristics of electronic systems. |
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发表于 2009-2-11 10:12:00
