Second Generation Controlled Current Conveyors (CCCII) and Their Applications - Current Conveyors: Variants, Applications and Hardware Implementations - page 259

V 0

I B3

X

I out

Z

−

Y

I B2

I B1

Y

V 1 V 2

Y

+

Z

Z

−

X

X

Fig. 9.15 Active-only instrumentation amplifier with electronically-controllable voltage gain [ 13 ]

It may be observed that the gain of this instrumentation amplifier is also
temperature-insensitive since V T is cancelled out.
An instrumentation amplifier realizable with only two CCCIIs was proposed by
Ercan et al. in [ 14 ] which is shown in Fig. 9.16 . A routine analysis of this circuit
reveals that the differential mode gain for this circuit is given by:

R A
2 R x

1

A dm ¼ ð 9 : 12 Þ

ð 1 þ sC b R A Þ

where the equivalent resistance (R A ) of the active resistor realized by the two
MOSFETs is given by:

1

R A ¼ ð 9 : 13 Þ

ʼ n C ox W ð = L Þ ð V C 2 V TH Þ

and C b is the output node capacitance

C b ¼ C A þ C Z 1 ð 9 : 14 Þ

If the non-ideal current gain and voltage gain of the CCCIIs are taken as ʱ and K

respectively, the common-mode gain is given by:

v cm ¼ ʱ

v 0 ð K 1 K 2 Þ R A

A cm ¼ ð : Þ

9 15

2 R x 1 ð þ sC b R A Þ

From the equation ( 9.15 ), it is clear that for nominal value of ʱ and K 1 ,K 2 ,A cm ! 0

and consequently, CMRR also . Also, the bandwidth can be fixed by fixing R A

while the gain can be electronically-controlled through R x .

!1