Hardware Reference
In-Depth Information
V
0
+V
DD
R
L
I
z
CUT
I
ref
Z
CCII
YX
I
x
I
ps
k I
ps
Q
1
Q
2
−V
SS
Fig. 8.23 BICS proposed by Hatzopoulos et al. [
10
]
8.9 Schmitt Trigger and Waveform Generators Using CCs
Because a translinear CCII+ has its input stage comprised of a four transistor mixed
translinear cell and the output current at the Z-terminal is a replica of the current
into X-terminal which is obtained by using a pair of current mirrors, it turns out that
the output current is a
Sinh
function of the differential input
V
y
V
x
. As a conse-
quence, the maximum charging current for the compensating capacitance
connected at Z-terminal (which in the absence of an external capacitor, is simply
the parasitic output capacitance looking into terminal-Z which is typical in the
range of 4-5 pF) is unlimited and theoretically infinite. This results in a very high
slew rate in case of CCII as compared to conventional op-amps. As an example for
CCII+ implemented from AD844 the slew rate is as high as 2,000 V/
μ
s as against a
very modest figure of 0.5 V/
A741op-amp.
In view of the above, it is obvious that a square wave generator of CCII+ is
expected to be much superior to that made from an op-amp; alternatively the
non-sinusoidal wave form generator made from CCII+ can be expected to perform
adequately for much higher frequency ranges than possible with op-amps. Moti-
vated by this superiority of CCII+ over the conventional op-amp, several
researchers have paid attention on devising novel realization of Schmitt triggers
and square/triangular wave form generators using CCIIs. In this section, we include
a discussion about some prominent ideas and circuits in this direction.
μ
s for the popular
μ
Search WWH ::
Custom Search