A simple quadrature oscillator using only cccdbas and ... - IEEE Xplore

A Simple Quadrature Oscillator Using Only CCCDBAs and Grounded Capacitors Winai Jaikla * Phamorn Silapan** and Montree Siripruchyanun † *

Electric and Electronic Program, Faculty of Industrial Technology, Suan Sunandha Rajabhat University, Dusit, Bangkok, 10300, THAILAND, Tel: +66-2-243-2240 Ext. 317, Fax: +66-2-241-5935, E-mail: [email protected] ** Electric and Industrial Program, Faculty of Industrial Technology, Uttaradit Rajabhat University, Muang, Uttaradit, 53000, THAILAND Email: [email protected] † Department of Teacher Training in Electrical Engineering, Faculty of Technical Education, King Mongkut’s Institute of Technology North Bangkok, Bangsue, Bangkok, 10800, THAILAND Tel: +66-2- 913-2500 Ext. 3328 Fax. +66-2-587-8255 Email: [email protected]

Abstract— This article presents a quadrature oscillator using Current Controlled Current Differencing Buffered Amplifiers (CCCDBAs) as active elements. The oscillation condition and oscillation frequency can be electronically/orthogonally controlled via input bias currents. The circuit description is very simple, consisting of merely 3 CCCDBAs and 2 grounded capacitors. Without any external resistors and using only grounded elements, the proposed circuit is then suitable for IC architecture. The PSPICE simulation results are depicted, the given results agree well with the theoretical anticipation. The power consumption is approximately 5.93mW at ±2V supply voltages. Index Terms- Quadrature oscillator, CCCDBA, CMOS, Voltage-mode, Current-mode

I.

both current and voltage-modes, provides flexibility and enables a variety of circuit designs. In addition, it can offer advantageous features such as high-slew rate, free from parasitic capacitances, wide bandwidth and simple implementation [4]. The literature surveys on recently proposed works show that the quadrature oscillator circuits using CDBA [5-7], have been reported. Unfortunately, these reported circuits suffer from one or more of following weaknesses: x Excessive use of the active and/or passive elements [5-7], x Lack of electronic adjustability [5-7], x Use of a floating capacitor which is not convenient to further fabricate in IC [5-6].

INTRODUCTION

Furthermore, the CDBA can not be controlled by the parasitic resistances at two current input ports so when it is used in some circuits, it must unavoidably require some external passive components, especially the resistors. This makes it not appropriate for IC implementation due to occupying more chip area, high power dissipation and without electronic controllability. Recently, Maheshwari and Khan have proposed the modified-version CDBA whose the parasitic resistances at two current input ports can be controlled by an input bias current and it is newly named current controlled current differencing buffered amplifier (CCCDBA) [8]. The purpose of this paper is to introduce a quadrature oscillator, based on CCCDBAs. The oscillation condition can be adjusted independently from the oscillation frequency with electronic method. The circuit construction consists of 3 CCCDBAs and 2 grounded capacitors. Practical consideration for non-ideal case is also investigated. The PSPICE simulation results are also shown, which are in correspondence with the theoretical analysis.

An oscillator is a basic important building circuit, which is frequently employed in electrical engineering works. Among several kinds of the oscillators, a quadrature oscillator is mostly/widely used because the quadrature oscillator can offer sinusoidal signals with 90° phase difference, as for example in telecommunications for quadrature mixers and single-sideband [1]. Presently, a current-mode technique has being been more popular than voltage-mode one. This is due to operating in low-voltage environment as in portable and battery-powered equipment. Since a low-voltage operating circuit becomes necessary, the current–mode technique is ideally suited for this purpose more than the voltage-mode one. Presently, there is a growing interest in synthesizing the current-mode circuits because of more their potential advantages such as larger dynamic range, higher signal bandwidth, greater linearity, simpler circuitry and lower power consumption [2]. Many active elements able to function in current-mode such as OTA, current conveyor, current differencing buffered amplifier (CDBA) and current differencing transconductance amplifier (CDTA), have been introduced to response these demands. The current differencing buffered amplifier is a reported active component especially suitable for a class of analog signal processing [3]. The fact that the device can operate in

II. A.

Current Controlled Current Differencing Buffered Amplifier (CCCDBA) Generally, its properties are similar to the conventional CDBA, except that input voltage of CCCDBA are not zero

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PRINCIPLE OF OPEREATION

and the CCCDBA has finite input resistance R p and Rn at the p and n input terminals, respectively. These intrinsic resistances are equal and can be controlled by the bias current I B as shown in the following equation ªV p º « » «Vn » «I » « z» ¬«Vw ¼»

where

ª Rp 0 « « 0 Rn «1  1 « ¬« 0 0 Rp

0º ª I p º »« » 0 0 » « In » . 0 0 » «Vz » »« » 1 0 ¼» ¬« I w ¼» 0

1

Rn

s2 

s  Rp1  Rp3  C C R1 R C1 R p1 R p 3 1 2 n1 n 2

0.

(3)

(1)

From Eq. (3), it can obviously be seen that the proposed circuit can be set to be oscillator if

.

8E I B

input bias currents of CCCDBA1, CCCDBA2 and CCCDBA3. From the CCCDBA properties in section A and routine analysis, the following system characteristic equation can be obtained

R p1

(2)

and C  NnC ox W /L is a physical parameter of CMOS.

Rp3 .

(4)

Eq. (4) is called as the condition of oscillation, which is achieved by setting

The symbol and the equivalent circuit of the CCCDBA are illustrated in Fig. 1(a) and (b), respectively.

I B3 .

I B1

(5)

Then, the characteristic equation of the system becomes s2 

Vp

IB

In

Vn

Iw

1

Rp

Vw

Iz

IB

Iz

Rn

I p  In

Z0

CCCDBA (a) Symbol (b) Equivalent circuit.

IB2

2

I B1

1

I B3

Fig. 2.

VO 2 C2

3

(6)

Substituting the intrinsic resistances as depicted in Eq. (2), it yields

Vz

(b) Fig. 1.

0.

From Eq. (6), the oscillation frequency of this system can be obtained as 1 . (7) Z0 C1C2 Rn1 Rn 2

(a)

Ip

1 C1C2 Rn1 Rn 2

VO1

§ 8E I B1 I B 2 ¨ ¨ C1C2 ©

1

·2 ¸ . ¸ ¹

(8)

From Eqs. (5) and (8), there can be seen that the oscillation condition can be electronically controlled by I B1 and I B 3 , while the oscillation frequency can be controlled by I B 2 . The quadrature voltage signals can be obtained at VO1 and VO 2 . From circuit in Fig. 2, the voltage transfer function from VO2 to VO1 is VO 2  s 1 . (9) VO1  s sC2 Rn 2 Under sinusoidal steady state, Eq. (9) becomes

C1

VO 2  jZ

Proposed Quadrature Oscillator.

The phase difference, I , between VO2 and VO1 is

Proposed Quadrature oscillator Fig. 2 depicts the proposed quadrature oscillator. The depicted bias currents; I B1 , I B 2 and I B 3 are respectively the

VO1  jZ

1

ZC2 Rn 2

e j 90q .

(10)

B.

I

90q

(11)

ensuring the voltages VO2 and VO1 to be in quadrature.

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Fig. 3.

Internal construction of CCCDBA

In addition, the quadrature signals in current-mode can be achieved by employing multiple-output Z terminal CCCDBAs for CCCDBA2 and CCCDBA3.

In this case, the oscillation condition and oscillation frequency are respectively changed to

C.

Non-ideality case For non-ideality case, each CCCDBA can be respectively characterized with the following equations I z1

D p I p  Dn In

(12)

E Vz .

(13)

and Vw

By straightforward analyzing the internal construction of each CCCDBA in Fig. 3, we will obtain the D p , D n and E as g m 6 g m19 g m13 g m 3 Dp  , (14) g m18  g m 6  g m 3 g m12  g m 6  g m 3

Dn

g m 5 g m19 g m17 g m 2 g m11 g m13  , g m16 g m18  g m 2  g m 5 g m10 g m12  g m 2  g m 5

(15)

§ g m 25 g m 24 · I1  ¨ ¸. Vz  g m 24  g m 25 © g m 22 g m 23 ¹

(16)

and

E

1

If transistors are matched, which are g m10 g m11 , g m 2 g m 3 g m 4 g m 5 g m 6 g m 20 g m 21 , g m12 g m13 , g m16 g m17 , g m18 g m19 , g m 22 g m 23 and g m 24 g m 25 , we will obtain D n # D p # E # 1 . g m1

In the case of non-ideality and reanalysis of the proposed quadrature oscillator in Fig. 2, it yields the system characteristic equation as s2  s

D D D EE 1 D p 3 E 3 Rn1  D p1 E 3 R p 3  n1 n 2 n 3 2 3  C1 Rn1 R p 3 C1C2 Rn1 Rn 2

0.

(17)

236

D p 3 E3 R1 D p1 E3 R3 , Z0

and

D n1D n 2D n 3 E 2 E 3 C1C2 Rn1 Rn 2

(18)

.

(19)

Actually, these deviations are very small and can be ignored. Practically, from Eqs. (14) to (16), . and  originate from intrinsic resistances and stray capacitances in the active elements. These errors affect the sensitivity to temperature and high frequency response of the proposed circuit, then the CCCDBA should be carefully designed to achieve these errors as low as possible. III.

SIMULATION REULTS

To prove the performances of the proposed oscillator, the PSPICE simulation program was used for the examinations. The PMOS and NMOS transistors employed in the proposed element in Fig. 3 were simulated by respectively using the parameters of a 0.35Pm TSMC CMOS technology [9]. Fig. 3 depicts schematic description of the CCCDBA used in the simulations. The CCCDBA was biased with r2V power supplies, the capacitors C1 and C2 are 0.1nF and I1 are 50PA. TABLE I DIMENSIONS OF THE MOS TRANSISTORS CMOS Transistors M1,M3-M5 M2 M6-M7 M8-M11 M12-M15 M16-M18 M19-M21 M22, M24 M23, M22

L( P m) / W ( P m) 1/10 1/8 5/10 1/12 1/4 1/30 5/30 3/9 2/7

2007 International Symposium on Communications and Information Technologies (ISCIT 2007)

Simulated C=0.1nF Theoretical C=0.1nF Simulated C=1nF Theoretical C=1nF Simulated C=10nF Theoretical C=10nF

VO (V)

1000

Fig. 4.

The simulation results of output waveforms during initial state

Fig. 4 and 5 show simulated quadrature output waveforms with bias currents; IB1 =IB2 = IB3 = 50PA. Fig. 6 shows the simulated output spectrum, where the total harmonic distortion (THD) is about 1.056%. Fig. 7 depicts the plots of the simulated compared to theoretical oscillation frequencies versus I B 2 variations where identical values of C1 and C2 are 0.1nF, 1nF and 10nF, respectively. The power consumption is approximately 5.93mW.

Frquency(KHz)

100

10

1

.1 1

10

100

IB2(PA) Fig. 7.

Oscillation frenquencies relative to bias current IB2 at various capacitances

REFERENCES

Fig. 5.

Fig. 6.

The simulation result of quadrature outputs

The simulation result of output spectrum

IV. CONCLUSIONS The quadrature oscillator based on CCCDBAs has been presented. The features of proposed quadrature oscillator are that: oscillation frequency and oscillation condition can be orthogonally adjusted via input bias currents, it consists of only 3 CCCDBAs and 2 grounded capacitors, which is suitable to fabricate in integrated circuit. The PSPICE simulation results are well agreed with the theoretical anticipation where the power consumption is approximately 5.93mW at ±2V supply voltages. The quadrature signals in current-mode can be achieved by employing multiple-output Z terminal CCCDBAs for CCCDBA2 and CCCDBA3.

[1] I. A. Khan and S. Khawaja, “An integrable gm-C quadrature oscillator,” Int. J. Electronics, vol. 87, no. 1, pp.1353-1357, 2000. [2] C. Toumazou, F.J. Lidgey and D.G. Haigh, Analogue IC design: the current-mode approach, Peter Peregrinus, London, 1990. [3] C. Acar and S. Ozoguz, “A new versatile building block: current differencing buffered amplifier suitable for analog signal processing filters,” Microelectronics Journal, vol. 30, pp. 157–160, 1999. [4] S. Ozoguz, A. Toker and C. Acar, “Current-mode continuoustime fully-integrated universal filter using CDBAs,” Electronics Letters, vol. 35, pp. 97–98, 1999. [5] A. U. Keskin, C. Aydin, E. Hancioglu and C. Acar, “Quadrature oscillator using current differencing buffered amplifiers (CDBA),” Frequenz, vol. 60, pp. 21-23, 2006. [6] W. Tangsrirat and S. Pisitchalermpong “CDBA-based quadrature sinusoidal oscillator,” Frequenz, vol. 61, pp. 102104, 2006. [7] J. W. Hong, “Current Differencing Buffered Amplifiers Based Single Resistance Controlled Quadrature Oscillator Employing Grounded Capacitors,” IEICE Transactions on fundamentals, vol. E85-A, pp. 1416-1419, 2002. [8] S. Maheshwari and I. A. Khan, “Current-controlled current differencing buffered amplifier: implementation and applications,” Active and Passive Electronic Components, vol. 27, pp. 219-227, 2004. [9] E. Yuce, S. Tokat, A. Kizilkaya and O. Cicekoglu, “CCIIbased PID controllers employing grounded passive components,” AEU-International Journal of Electronics and Communications, vol. 60, no. 5, pp. 399-403, 2006.

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