Hardware Reference
In-Depth Information
V
2
I
01
I
02
V
1
Z+
Z+
X
Y
Z+
C
2
X
Y
Z+
Z−
Z+
Z−
C
3
C
1
I
C
I
D
I
A
I
B
I
03
Y
Z+
X
Fig. 9.42 A third order quadrature oscillator using CCCIIs proposed by Maheshwari [
41
]
r
I
01
I
02
C
1
C
2
1
CO
I
03
¼
I
01
and FO
f
0
¼
ð
9
:
56
Þ
:
:
ˀ
V
T
It is, therefore, seen that CO can be controlled by I
03
whereas f
0
is controllable
through I
02
. SPICE simulation results have confirmed very good correspondence
between frequency and controlling current I
02
.
Quadrature oscillators have attracted lot of attention in analog circuits literature
because of their wide spread use in communication and instrumentation systems.
Quadrature oscillators have also been realized by using CCs by a number of
researchers. In the following we present an exemplary third order quadrature
oscillator which is capable of providing two voltage outputs which are in quadrature
as well as four current outputs using CCCIIs. Two of which are also in quadrature
the circuit enjoys non-interactive frequency control while employing three
grounded capacitors. This circuit is shown in Fig.
9.42
.
With identical capacitors the CO and FO for this circuit are given by:
r
1
R
x
2
R
x
3
1
CO
R
x1
¼
R
x3
andFO
f
0
¼
ð
9
:
57
Þ
:
:
2
ˀ
C
Using SPICE simulation based upon a CMOS CCCIIs (see Fig. 3 of [
41
]) biased
from
m CMOS process parameters. It has been confirmed that
the circuit can function quite well at oscillation frequency of the order of 4 MHz
with THD of
2.5 V using 0.5
μ
1% for voltage outputs.
There appears to be enough scope in devising new topologies for evolving fully
uncoupled oscillators using CCCIIs which provide independent control of CO
through separate external bias currents and may provide linear control of FO
through simultaneous variation of two external bias currents. Furthermore, any
CMOS CCCIIs based circuit capable of providing linear control of FO does not
<
2 % for current outputs and
<
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