Hardware Implementations of CCs Using Off-the-Shelf ICs - Current Conveyors: Variants, Applications and Hardware Implementations - page 20

Fig. 2.4 Implementation of
CCII+ and CCII proposed
by Senani [ 3 ]

I B

i y +

g m

Y

R 01 Z

+

i z

−

X

−

i x

Fig. 2.5 Implementation of
CCI+ and CCI

R 02 I B

proposed

i y

+

by Senani [ 3 ]

g m

Y

R 01 Z

+

i z −

X −

i x

It should be recalled that the CCII implementation by Black, Friedmann and
Sedra requires an integrated circuit

A749 containing an op-amp with uncommitted
output collectors, which when augmented by the introduction of several PNP and
NPN transistors externally realizes a CCII. On the other hand the Bakhtiar-
Aronhime circuit requires 5 op-amps along with 13 external resistors. In compar-
ison with these approaches, the op-amp-OTA based implementation is simpler and
more versatile because it can realize CCII as well CCI (positive and negative both).

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2.2.4 Huertas s Entirely Op-Amp Based CC Implementation

'

Huertas [ 4 ] presented an entirely op-amp version of Senani s op-amp-OTA based

circuit [ 3 ] which is shown here in Fig. 2.6 . This circuit can be implemented from a
single dual op-amp IC chip. The circuit as shown realizes a CCII; for realizing a
CCI an additional resistor needs to be connected between the non-inverting input
and the output of the first op-amp. The circuit in the dotted box acts as a differential
voltage controlled current source (DVCCS) which is what an OTA does. An
analysis of the circuit shows that it is not really necessary to take r 1 ¼

'

r 2 and

r 3 ¼ r 4 as originally taken by Huertas. The same results can be obtained by selecting

component values to satisfy the following condition.

r 1
r 3 ¼

r 2
r 4 ¼

r
r 0

ð 2 : 1 Þ

As compared to the op-amp-OTA-based circuit of [ 3 ] this circuit was claimed to
provide the following advantages: (i) with appropriate choice of the op-amps this
circuit can provide a better frequency response (ii) the differential input impedance
of an OTA which is typically of the order of 20 K , imposes an upper bound on the

value of resistor r; using only op-amps relaxes this limitation (iii) it is possible to
achieve offset correction in this circuit by appropriate choice of resistors r 1 ,r 2 ,r 3 ,r 4

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