Hardware Reference
In-Depth Information
Fig. 7.12 Sinusoidal
oscillator proposed by
Abuelma
'
atti and Khan [
30
]
y
z
CCII+
x
R
1
R
2
y
z
CCII+
x
R
4
R
3
C
p
parasitic input resistance R
x
and Z-port parasitic impedance consisting of R
p
in
parallel with C
p
for both the current conveyors and assuming them identical, was
proposed by Abuelma
atti and Khan in [
30
] and is shown here in Fig.
7.12
.
A straight forward analysis shows that the condition of oscillation and the
frequency of oscillation of this circuit are given by:
'
R
1
R
3
þ
ð
R
x
Þ
R
2
R
4
0
R
1
R
3
R
x
R
2
þ
CO
R
2
R
4
R
1
R
x
,FO
:
ω
¼
ð
7
:
31
Þ
:
C
p
C
z
þ
C
y
ð
R
4
Þ
Thus, two interesting features of this circuit are: requirement of only a single
grounded capacitor and incorporation of all the parasitic impedances of the CCs
into the design thereby incorporating their effect,
a priori,
in the design. The latter
feature means that this circuit can be designed to generate frequencies much higher
than those possible with other two-CC-based circuits described earlier. That this is
indeed so has been demonstrated by the authors of [
30
] realizing CCII+ s from
AD844 ICs from which oscillation frequencies up to 11.11 MHz have been attained
easily.
7.5 Quadrature and Multi-phase Oscillators
A special type of oscillators known as quadrature oscillators which are capable of
generating two sinusoidal signals having a phase difference of 90
(in quadrature)
which are useful in quadrature mixers and single sideband modulators. In measure-
ment applications, quadrature oscillators are useful in vector generators and selec-
tive voltmeters. In addition four-phase quadrature oscillators find applications in
sub-harmonic mixers to reduce noise and intermodulation distortion. Lastly,
multiphase oscillators may find applications in power electronic systems and
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