Hardware Reference
In-Depth Information
unity gain active elements proposed by Kuntman et al. [
35
]. Assuming ideal CCII+
s and voltage followers, the current transfer function for the circuit of Fig.
6.40a
is
given by:
i
0
i
in
¼
s
ð
for R
¼
1
ʩ
and C
¼
1F
Þ
ð
6
:
60
Þ
þ
2
s
þ
2
s
2
þ
s
3
1
Using RC-CR transformation, another BPF can be obtained whose current transfer
function is given by:
i
0
i
in
¼
s
2
ð
for R
¼
1
ʩ
and C
¼
1F
Þ
ð
6
:
61
Þ
1
þ
2
s
þ
2
s
2
þ
s
3
The circuits, when implemented with AD844 ICs used to realize CCII+ as well as
voltage followers, showed excellent correspondence with theoretical responses
when designed for
f
0
¼
150 KHz with AD844 biased from
12 V DC power
supplies with load resistance R
L
¼
13 k
ʩ
, equal valued R-C components taken as
1k
ʩ
and 1 nF.
6.2.5 MOSFET-C Integrators and Filters Using CCII
It has been well known that MOS resistive circuit (MRC) can cancel completely the
even and odd MOS nonlinearities of the four matched MOSFETs employed therein.
Assuming ideal CCII+ and the devices in MRC to be identical (matched) and
operated in triode region, the expression for its output voltage of the circuit of
Fig.
6.41
is given by:
Z
1
RC
1
C
ox
L
V
GA
V
out
¼
V
in
d
˄
, where
R
¼
ð
6
:
62
Þ
ʼ
f
j
j
j
V
GB
j
g
where V
in
¼
V
2
) and the positive or negative R is used to represent an
inverting or non-inverting integrator.
This integrator can be easily employed to design higher order filters. In [
37
]it
has been demonstrated in the design of a third order low pass filter based upon
doubly-terminated ladder filter with 0.01 dB pass band ripple up to 1 MHz. The
functionality of this integrator has also been verified by designing a voltage-
controlled oscillator realized by a bipolar CC, the MRC and a Schmitt Trigger
(both implemented from CD 4007). The structure of Fig.
6.41
is suitable for
realizing high frequency MOSFET-C filters using CCs.
(V
1
Fig. 6.40 (continued) cascading the two circuits of Fig.
6.40
(a) referred to as cell-one and cell-
two respectively. (c) A typical output waveform (input current 1 mA, 150 kHz sinusoidal wave:
vertical axis 5 V/div., horizontal axis 2
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