Hardware Reference
In-Depth Information
1
=
2
þ
tan
n
2
K
¼
1
ð
7
:
40
Þ
Both the circuits are practically realizable with CCII+ from AD844 ICs with
reasonably reduced total components than those required in other design method-
ologies using CCs [
21
,
27
,
33
,
34
].
7.6 Explicit Current Output (ECO) SRCOs
With the advent of current mode signal processing particularly current mode filters,
rectifiers, instrumentation amplifiers etc., it is imperative that for testing of such
circuits one should have signal generators capable of providing an
explicit
current
output from a high output impedance terminal. In this context, therefore, sinusoidal
oscillators having
explicit current output
from high output impedance node are
obviously potential candidates for such applications. Several such oscillators have
been reported in literature such as those in [
29
,
32
,
38
,
42
,
46
,
55
,
56
].
Senani and Gupta [
38
] proposed two methods for devising such oscillators,
resulting thereby in different configurations which are shown here in Fig.
7.19
.
The circuit of Fig.
7.19a
has been synthesized by simulating a negative resistor
with a CCI in parallel with series RLC branch, wherein the series RL part is created
by two unity gain voltage followers B
1
and B
2
, resistors R
1
and R
2
and capacitance
C
2
thereby leading to an equivalent RL impedance with R
eq
¼
R
1
and equivalent
inductance L
eq
¼
C
2
R
1
R
2
. The resulting oscillator, therefore, has the following
characterization:
r
1
C
1
C
2
R
1
R
2
CO
R
1
¼
R
3
;
FO
:
ω
0
¼
ð
7
:
41
Þ
:
On the other hand, the second circuit (Fig.
7.19b
) is derived through the application
of the state variable synthesis technique proposed by Senani and Gupta in [
58
-
60
]. In this case, assuming C
1
¼
C
2
¼
C, CO is same as in Eq. (
7.41
) while the
frequency of oscillation is given by:
1
C
p
ω
0
¼
ð
7
:
42
Þ
R
2
R
3
A comparison with the other alternative AGPE oscillators mentioned earlier is of
interest. In this context, it may be noted that the remaining oscillators quoted earlier
suffer from one or more of the following drawbacks: use of more than three
resistors and/or more than two capacitors as in [
32
,
39
]; non-availability of single
element controls for CO and FO as in [
29
,
55
] and requirement of more active
elements than those in the circuit of Fig.
7.19
considered here [
56
].
Search WWH ::
Custom Search