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A Novel Versatile Circuit functioning as both Filter

and Oscillator based on CCCCTAs

Phamorn Silapan

Electric and Industrial Program, Faculty

of Industrial Technology,

Uttaradit Rajabhat University, Muang,

Uttaradit, 53000, THAILAND

phamorn@mail.uru.ac.th

Winai Jaikla

Electric and Electronic Program, Faculty

of Industrial Technology,

Suan Sunandha Rajabhat University,

Dusit,

Bangkok, THAILAND

winai.ja@ssru.ac.th

lower power consumption [3]. However, from our

investigations, we have seen that in previous literature,

oscillators require too many components and component

matching conditions [4]. Some universal filters require a

floating capacitor, which is not ideal for IC implementation

[5]. In addition, each circuit can work as only one function,

either quadrature oscillator or universal filter. It would be

preferable to compact the circuits/systems if a circuit can

work for several functions.

Recently, the network which can function both as filter and

as oscillator has been firstly reported [6], it is called

‘Filtillator’. Although the circuit description is simple, the

output current signals are provided at passive element

terminals. Thus, it is needed to employ a current mirror or

current buffer to obtain the usable output currents, this makes

the circuit more complicated. In addition, the output signals

offer a high total harmonic distortion (THD), up to 4.18%.

The purpose of this paper is to introduce a novel current-

mode universal biquad filter, based on the novel active

building block recently proposed, named as CCCCTA [7],

providing five standard transfer functions (low-pass, high-

pass, band-pass, band-reject, all-pass functions) to achieve the

mentioned requirements. The natural frequency can be

adjusted independently from the quality factor. Moreover, in

the case of no input current and under appropriated condition,

the proposed circuit can provide quadrature sinusoidal signals

in both voltage-mode and current-mode simultaneously with

a low THD without changing any circuit topology. The circuit

construction consists of only 2 CCCCTAs and 2 grounded

capacitors (beneficial to an IC Implementation [8]). The

PSPICE simulation results are also shown, which are in

correspondence with the theoretical analysis.

Montree Siripruchyanun

Department of Teacher Training in

Electrical Engineering, Faculty of

Technical Education,

King Mongkut’s University of

Technology North Bangkok,

Bangkok, THAILAND

mts@kmutnb.ac.th

Abstract- A circuit which can function both as quadrature

oscillator and as a universal biquad filter (low-pass, high-pass,

band-pass, band-reject and all-pass functions) is introduced in

this paper. Working as quadrature oscillator, the oscillation

condition and oscillation frequency

independently with the input bias currents. Functioning as a

universal biquad filter, the quality factor and natural frequency

can be tuned orthogonally via the input bias currents. The

proposed circuit can work as either a quadrature oscillator or a

universal biquad filter without changing circuit topology. The

proposed circuit description is very simple, consisting of merely

2 current controlled current conveyor transconductance

amplifiers (CCCCTAs) and 2 grounded capacitors. Without any

external resistors and using only grounded elements, this circuit

is thus suitable for IC architecture. The PSPICE simulation

results are depicted, and the given results agree well with the

theoretical anticipation. The maximum power consumption is

approximately 3.78mW at ±1.5V power supplies.

can be adjusted

I.

INTRODUCTION

It is well accepted that an oscillator and a filter are 2

important basic building blocks which are frequently

employed. A quadrature oscillator is widely used because it

can provide two sinusoids with 90? phase difference, for

example in telecommunications for quadrature mixers and

single-sideband systems [1]. Similarly,

applications and advantages in the realization of various

active transfer functions, called universal biquad filters, have

received considerable attention. A universal filter may be

used in phase locked loop FM stereo demodulators and

crossover networks, used in three-way high fidelity

loudspeakers [2]. However, a current-mode universal filter

has been more popular than the voltage-mode type. This is

due to operating in low-voltage environments, such as

portable and battery-powered equipments. Since a low-

voltage operating circuit becomes necessary, the current-

mode technique is ideally suited for this purpose, more so

than the voltage-mode. Presently, there is a growing interest

in synthesizing current-mode circuits because of their many

potential advantages, such as larger dynamic range, higher

signal bandwidth, greater linearity, simpler circuitry, and

the modern

II. CIRCUIT CONFIGURATION

A. Basic Concept of CCCCTA

CCCCTA properties are similar to the conventional CCTA,

except that the CCCCTA has finite input resistance Rx at the x

input terminal. This parasitic resistance can be controlled by

the bias current IB1 as shown in the following equation

1367978-1-4244-2342-2/08/$25.00 ©2008 IEEE.

Page 2

0

R

0

1

0

0

0

0

0

0

0

0

0

1

0

yx

y

x

x

zz

m

oo

II

V

V

I

I

V

V

g

⎡

⎢

⎢

⎢

⎢

⎢

⎣

⎤

⎥

⎥

⎥

⎥

⎥

⎦

⎡

⎢

⎢

⎢

⎢

⎢

⎣

⎤

⎥

⎥

⎥

⎥

⎥

⎦

⎡

⎢

⎢

⎢

⎢

⎣

⎤

⎥

⎥

⎥

⎥

⎦

=

±

, (1)

where

1

2

T

x

B

V

I

I

R

=

, (2)

and

2

2

B

V

m

T

g

=

, (3)

where

V is the thermal voltage. The symbol and equivalent circuit

of the CCCCTA are illustrated in Figs. 1(a) and (b),

respectively.

m

g is the transconductance gain of the CCCCTA and

T

1

B

I

y

x

z

o

CCCCTA

yi

xi

zi

oi ±

2

B

I

y

V

x

V

z V

o V

(a)

1

R

y

x

o

xi

xi

mZ

g V

±

x

z

(b)

Fig. 1. The CCCCTA (a) symbol (b) equivalent circuit

x

y

o1

z2

CCCCTA 1

Iin

C1

IB1

IB2

z1

ILP

IBP

IHP

y

x

o1

z2

CCCCTA 2

IB3

IB4

z1

C2

z3

o2

o2

IBP

IBS

Iin

IAP

Figure 2. Proposed circuit working as universal filter

B. The proposed circuit operating as an universal biquad

filter

Fig. 2 demonstrates the presented circuit schematic

working as a universal filter. The depicted bias

currents:

12

,

3

, and

4

are the input bias currents of

CCCCTA1 and CCCCTA2 respectively. From the CCCCTA

properties in Section II.A and routine circuit analysis, the

following current transfer functions are obtained

BI ,

BI

BI

BI

2

2

212

21212

1

HP

I

in

xmm

xx

I

s

R g

R C

g

ss

R C C

=

⎛

⎜

⎝

⎞

⎟

⎠

−

++

, (4)

LP

I

in

I

=

2

212

2

212

2

R g

1212

1

m

x

xmm

xx

g

R C C

⎞

⎟

⎠

R g

R C

g

ss

R C C

⎛

⎜

⎝

−

++

, (5)

and

()

21

2

2

212

21212

1

1

xm

x

BP

I

in

xmm

xx

s

R C

I

R g

R C

g

ss

R C C

−

=

⎛

⎜

⎝

⎞

⎟

⎠

−

++

. (6)

Moreover, the band-stop and the all-pass functions can be

obtained from the currents IBS=Iin-IBP, IAP=IBS-IBP. All output

responses can be directly obtained by using either multiple-

output CCCCTAs or a current follower. Consequently, the

band-stop and all-pass functions can be obtained as

g

s

I

I

R g

s

R C

⎝

1

x

R g

s

R C

I

I

R g

s

R C

⎝

From Eqs. (4)-(8) the parameter

as

g

R C C

Substituting the intrinsic resistances as depicted in Eqs. (2)-

(3) and for easy consideration, if

III

==

, Eq. (9) can be reduced to

I

V C

From Eqs. (9) and (10), if

B

I

realized by using a programmable current mirror [9-10]. The

pole frequency and quality factor are subsequently modified

to be

I

V C

From Eqs. (10)-(11), it can be seen that the natural frequency

(ω0) can be adjusted linearly and independently from the

quality factor (Q0) by varying

factor can be adjusted by k . Thus, bandwidth (BW) is given

by

ω

=

2

2

212

2

212

21212

1

m

BSx

in

xmm

xx

R C C

⎞

⎟

⎠

⎞

+

⎟

⎠

⎞

+

⎟

⎠

ω and

g

s

R C C

+

=

⎛

⎜

−

++

, (7)

and

2

212

212

g

12

2

212

2121

Q are expressed

2

1

mm

xx

AP

in

xmm

xx

g

s

R C C

s

R C C

⎛

⎜

⎝

⎛

⎜

−

−

=

−

+

. (8)

00

2

0

212

m

x

ω =

,

()

221

0

21221

1

mx

xxm

g R C

R g

−

Q

R C C

=

. (9)

12

CCC

==

and

34BBB

0

B

T

ω =

,

0

2

2

4

B

B

, which can be easily

B

I

−

Q

II

=

. (10)

2B

kI

=

0

B

T

ω =

,

0

2

−

4

Q

k

=

. (11)

BI or C, while the quality

0

2

0

4

2

BB

T

II

BW

QV C

−

=

. (12)

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x

y

o1

z2

CCCCTA 1

C1

IB1

IB2

z1

IO2

IO1

y

x

o1

z2

CCCCTA 2

IB3

IB4

z1

C2

z3

o2

o2

VO1

VO2

Figure 3. Proposed circuit working as quadrature oscillator

C. The proposed circuit operating as a quadrature

oscillator

If no input current is applied to the circuit as shown in

Fig. 3, the system characteristic equation can be expressed as

1

xm

R g

s

R C

⎝⎠

From Eq. (13), it can be seen that the proposed circuit can be

set to be an oscillator if

1

R

Eq. (14) is called the condition of oscillation, and this is

achieved by

32

4BB

II

=

. Thus, the characteristic equation of

the system becomes

g

s

R C C

From Eq. (15), the oscillation frequency of this system can be

obtained as

g

R C C

It can be found that the oscillation frequency (ω0) can be

controlled by bias currents. Additionally, the oscillation

condition can be tuned by

oscillation frequency. The quadrature sinusoidal signals can

be simultaneously obtained both as current-mode at IO1 and

IO2 and voltage-mode at VO1 and VO2.

2

212

21212

0

m

xx

g

s

R C C

⎛

⎜

⎞

⎟

−

++=

. (13)

1

2

m

x

g

=

. (14)

2

2

212

0

m

x

+=

. (15)

234

0

2

212

12

mBB

x

T

I I

V C C

ω ==

. (16)

2

BI

without affecting the

6

Q

7

Q

8

Q

9

Q

1

Q

3

Q

2

Q

4

Q

5

Q

10

Q

11

Q

12

Q

13

Q

x

1BI

y

1z

CC

V

EE

V

2 o

18

Q

19

Q

16

Q

17

Q

2

BI

2z

1o

14

Q

15

Q

20

Q

21

Q

22

Q

23

Q

24

Q

25

Q

26

Q

Figure 4. Circuit description of current controlled current conveyor

transconductance amplifier

III. SIMULATION RESULTS

To prove the performances of the proposed circuit, the

PSPICE simulation program was used for the examination.

The PNP and NPN transistors employed in the proposed

circuit were simulated by respectively using the parameter of

the NR200N and PR200N bipolar transistors of ALA400

transistor array from AT&T [11]. Fig. 4 depicts schematic

description of the CCCCTA used in the simulations. The

CCCCTAs were biased with

capacitors C1 and C2 are 1nF. Fig. 5 illustrates the magnitude

responses of the proposed universal filter. It shows that the

proposed filter provides LP, HP, BP, BS and AP responses at

the same time. The result in Fig. 6 confirms that the quality

factor can be adjusted by

2

pole frequency, as analyzed in Eq. (10). Fig. 7 shows gain

responses of the band-pass function where

25µA, and 60µA, respectively. This shows that pole

frequency can be adjusted without affecting the quality factor,

as depicted in Eq. (11).

50

1.5V

±

power supplies, the

BI

which is independent of the

BI is set to 10µA,

Frequency (Hz)

Gain (dB)

1k

3k

10k

30k100k

300k

1M3M

10M

-100

-50

0

ILP/Iin

IAP/Iin

IHP/Iin

IBP/Iin

IB1=100

C1=C2=10 nF

IB2=10 IB3=IB4=20

IBS/Iin

Figure 5. Gain responses of the proposed circuit working as universal filter

Gain (dB)

Figure 6. BP responses for different values of

2

BI

Gain (dB)

Figure 7. BP responses for different values of

Figs. 8, 9, and 10 show the responses when the proposed

circuit operates as quadrature oscillator with bias

currents

1

100

A

μ

=

,

2

203

=

BI

BI

BIA

μ

and

34

50

BB

IIA

μ

==

,

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Page 4

where the total harmonic distortion (THD) is about 1.09%.

Fig. 11 depicts the plots of the simulated and theoretical

oscillation frequencies versus the bias currents,

C1 and C2 are identical values of 0.1nF, 1nF, and 10nF. It is

seen that the simulation results are in accordance with the

theoretical analysis as shown in Eq. (16). The maximum

power dissipation is about 3.75mW for

voltages.

100

4,

BI

where

1.5V

±

supply

IO( A)

IB1= 100

IB3= IB4=50

IB2= 203

C1=C2=1nF

Time ( s)

0

10

20

30 40

50

60

70 80

90

100

-100

-50

0

50

Figure 8. The simulation results of waveforms working as quadrature

oscillator

IO( A)

Figure 9. The simulation results of current waveforms of quadrature

oscillator

40

VO1

VO2

Time ( s)

70

75 80

8590 95

100

-40

-20

0

20

Figure 10. The simulation results of voltage waveforms of quadrature

oscillator

IV. CONCLUSIONS

The novel circuit, which can function both as a quadrature

oscillator and as a current-mode universal biquad filter,

providing completely standard functions, has been presented.

The proposed circuit can work as either a quadrature

oscillator or a universal biquad filter without changing a

circuit topology. Working as a current-mode universal biquad

filter, the quality factor and pole frequency can be tuned

orthogonally via the input bias currents. With no input current

and under suitable condition, the proposed circuit functions as

a quadrature oscillator. Its oscillation condition and

oscillation frequency can be also adjusted independently by

the input bias currents. In addition, it is also found that the

circuit can be controlled electronically and the useful

frequency range up to a hundred megahertz range. The

simulation results are well agreed with the theoretical

anticipation. Since it consists of 2 CCCCTAs and 2 grounded

capacitors, this circuit is thus suitable for IC architecture to

employ in portable electronic equipments.

REFERENCES

[1]

I. A. Khan, and S. Khawaja, “An integrable gm-C quadrature

oscillator,” Int. J. Electronics, vol. 87, vol. 1, pp. 1353-1357, 2000.

M. A. Ibrahim, S. Minaei, and H. A. Kuntman, “A 22.5 MHz current-

mode KHN-biquad using differential voltage current conveyor and

grounded passive elements,” Int. J. Electron. Commun. (AEU), vol.

59, pp. 311-318, 2005.

C. Toumazou, and F. J Lidgey. “Universal active filter using current

conveyors,” Electron. Lett., vol. 22, pp.662-664, 1986.

C. Toumazou, F. J. Lidgey, and D. G. Haigh, Analogue IC design: the

current-mode approach, London: Peter Peregrinus, 1990.

M. Sagbas, and K. Fidanboylu “Electronically tunable current-mode

second-order universal filter using minimum elements,” Electron.

Lett.,vol. 40 pp. 2-4, 2004.

P. Silapan, l T. Srisaku, W. Jaikla, and M. Siripruchyanun,

“CCCDTA-based filtillator (filter and oscillator),” 30th Electrical

Engineering Conference, pp. 897-900, 2007.

M. Siripruchyanun, M. Phattanasak and, W. Jaikla, "Current

controlled current conveyor transconductance amplifier (CCCCTA): a

building block for analog signal processing," International Symposium

on Communications and Information Technologies 2007, pp. 209-212,

2007.

Y. Sun and J. K. Fidler, “Synthesis and performance analysis of

universal minimum component integrator-based IFLF OTA-grounded

capacitor filter,” IEE Proc. Circuit Devices Syst., pp. 143:107-114,

1996.

D. Chandrika, R. A. Jaime, L. M. Antonio, and Ramon C.,

“Architectures of class AB CMOS mirrors with programmable gain,”

Analog Integ. Circuit Signal Process, vol. 42, pp. 197–202, 2005.

[10] B. Sedighi and M. S. Bakhtiar, “Variable gain current mirror for high-

speed applications,” IEICE Electron. Express, vol. 4, pp. 277-281,

2007.

[11] D. R. Frey, “Log-domain filtering: an approach to current-mode

filtering,” IEE Proc. Circuit Devices Syst., vol. 140, pp.406-416, 1993.

[2]

[3]

[4]

[5]

[6]

[7]

[8]

[9]

IB4(μ μA)

1 10100

Frequency (MHz)

.01

.1

1

10

100

1000

Theoretical C=10nF

Simulated C=10nF

Theoretical C=1nF

Simulated C=1nF

Theoretical C=0.1nF

Simulated C=0.1nF

Figure 11. Oscillation frequencies against bias currents for various

capacitances

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