Other Building Blocks Having MTC or CC at Front-end and Their Applications - Current Conveyors: Variants, Applications and Hardware Implementations - page 349

11.6 Current Controlled Current-differencing
Transconductance Amplifier (CC-CDTA)

The current differencing transconductance amplifier (CDTA) was introduced by
Biolek [ 41 ] as a new versatile building block for current-mode analog signal
processing. It is a five-port building block having two inputs and three outputs
with the following characterizations. The two inputs labeled as p and n are low
impedance terminals having virtual ground at their inputs. The difference of the two
input currents I p and I n is made available from the high output impedance
Z-terminal where an external impedance may be connected as a load thereby
creating a voltage V z which is given as input to an internal OTA which creates
two current outputs called I x+ and I x which are respectively given by I x+ ¼ g m V z

and I x ¼ g m V z . This is shown in Fig. 11.9 .

A CC-CDTA is an extension of the concept of CDTA and is characterized by
V p ¼ R p I p ,V n ¼ R n I n ,I z ¼ I p -I n ,I x ¼ g m V z where R p ¼ R n ¼ V T /2I B and g m ¼ I C /

2V T which is shown in Fig. 11.10a .
A novel application of this implementation is the current mode multiplier/
divider shown in Fig. 11.10b which has the output current given by

I A I C
8 I B

I O ¼ ð Þ

11 : 7

From the above it is seen that I O is result of either multiplication of I A and I C ,or
dividing I A or I C by I B . However, a limitation of this circuit is that it is only two
quadrant multiplier/divider. On the other hand, a merit of this circuit is that the
functions performed by this circuit are temperature insensitive since the terms
involving V T have been cancelled out and do not appear in the output equation.
For a number of interesting applications of the CC-CDTAs see [ 41 - 73 ].

11.7 Current Controlled Current Conveyor
Transconductance Amplifier (CCCC-TA)

This building block was proposed by Siripruchyanun and Jaikla [ 74 ] and is char-
acterized by the following terminal equations: I y ¼ 0, V x ¼ V y +I x R x , where

R x ¼ I B2 /2V T .

An exemplary implementation of this building block is shown in Fig. 11.11 from
where it can be seen that the input front end of this building block also happens to be
the MTC which results in the current controllability of its R x .
An interesting application of this building block was demonstrated by
Siripruchyanun and Jaikla [ 74 ] in realizing a universal current-mode biquad. The
novelty of this circuit, shown here in Fig. 11.12 , lies in using only a single active
building block for realizing all the five standard filter responses with both grounded

V T /2I B1 ,I Z ¼ I x and I 0 ¼ g m V z where g m ¼