Hardware Reference
In-Depth Information
Since the current conveyors were already introduced in the literature, a number
of research groups around the world also started looking for the possibility of
realizing sinusoidal oscillators using CCs in general and SECOs/SRCOs in partic-
ular. After a considerable research it was found that a canonic SECO/SRCO using a
single CC can be realized with only five passive components namely, either three
resistors or two capacitors or with three capacitors and two resistors. With the
introduction of a large variety of extensions of the basic current conveyor types, the
research on the realization of SRCOs including quadrature and multi-phase oscil-
lators has still continuing. Because of the enormity of the literature on SRCOs using
CCs, this chapter focuses only on SECOs/SRCOs realizable with the basic types of
current conveyors namely CCI
only with the circuits realizable from
other modified variants of current conveyors have been reserved for a separate
treatment in subsequent chapter (Chap.
13
) of this monograph.
In the subsequent sections of this chapter, we focus on the single-CC-based
SECOs/SRCOs and a number of other varieties of sinusoidal oscillator configura-
tions evolved over the past 35 years [
1
-
56
] using the basic three-terminal types
of CCs.
and CCII
7.2 Single-CC SRCOs
It is interesting to note that although both CCI and CCII had distinctly different
terminal characterizations as compared to the ubiquitous op-amp, the equality of
the voltages between Y and X terminals was quite similar to that of an infinite gain
op-amp (when connected in a negative feedback arrangement) which was respon-
sible for a number of circuits which were derived in the initial phase of research on
current conveyors through analogy of corresponding op-amp-based circuits. Thus, a
number of early current conveyor based oscillators which were based upon classical
Wien bridge oscillator and its variants using op-amp were obvious, for instance see
[
1
,
24
,
29
,
36
] and therefore, they also suffered from the same limitations or
difficulties as their op-amp-based counterparts. Besides this there have been a
number of other single-CC based single frequency [
11
,
12
,
15
,
20
] as well as
variable frequency [
3
-
10
,
13
,
16
,
19
,
20
]
1
oscillators reported in literature.
In the following, however, we focus on only variable frequency oscillators
capable of providing frequency control
through a single variable element
(a capacitance or resistance).
In fact, the first SECO using a single CCII+ was proposed by Soliman in [
3
]
which is shown here Fig.
7.1
. This circuit is characterized by the condition of
oscillation (CO) as
1
Apart from a single CC, this circuit, however, also incorporates an OTA.
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