Other Building Blocks Having MTC or CC at Front-end and Their Applications - Current Conveyors: Variants, Applications and Hardware Implementations - page 345

a

Y Z

Y

CCII−
X

Z

X

b

1

Y

1 3

CCII−

3

Z

X

2 4

X

4

CCII−

Z

2

Y

c

1

Y
CCII+
X

3

Z

X
CCII+
Y

4

Z

2

Fig. 11.3 Practical realization of FTFN using current conveyor (a) nullor equivalent of the CCII

(b) FTFN implementation using two CCII (c) FTFN implementation using two CCII+ (realizable

using two AD844s)

11.4 Operational Trans-Resistance Amplifier (OTRA)

An operational transresistance amplifier has two input terminals with input impedance
being ideally zero thereby providing a virtual ground at both the inputs. The difference
of the input currents applied at the two input terminals flows out of a node where
the transresistance gain a set up by a resistance R m thereby leading to the equation
V 0 ¼ R m (I 1 -I 2 ). When used in negative feedback, the infinite transresistance gain R m

forces the two inputs current to be equal-a property which can be considered to be
the dual of that available in a voltage- mode op-amp. The internal circuit architecture
of an OTRA employs two input cells which are essentially mixed-translinear-cells as
employed in the front end of a CCII. Since the OTRA has virtual ground at its
both inputs and has low impedance voltage output, most of the effect of the parasitic
capacitances becomes ineffective. Due to these advantageous features, the OTRA has
been employed extensively in realizing immittance simulator topologies, Schmitt
trigger, monostable/bi-stable multivibrators, sinusoidal oscillators and SRCOs,
for instance, see references [ 23 - 26 ] and those cited therein. A CC based implemen-
tation of the OTRA is shown in Fig. 11.4 .