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Poster Paper Proc. of Int. Colloquiums on Computer Electronics Electrical Mechanical and Civil 2011

CMOS Sinusoidal Oscillator using Current Conveyor Mourina Ghosh1, Subhajit Bhattacharya2, Ashish Ranjan3, Sajal K. Paul4 Department of Electronics Engineering, Indian School of Mines, Dhanbad, India 1 mourina_06@rediffmail.com, 2subhajit_ece@rediffmail.com, 3 ashish.ism@rediffmail.com, 1sajalkpaul@rediffmail.com Abstract: A gain controlled sinusoidal oscillator circuit based on current controlled current conveyors (CCCII) is introduced. The circuit contains three CCCIIs and two grounded capacitors. The amplitude of the output current can be controlled electronically. The CCCII has been implemented using 0.35µm CMOS technology and the PSPICE simulation results are given.

 I Y  0 0 0   V Y   V   1 R 0   I X  X  X   I Z   0  1 0   V Z 

(1)

The plus and minus signs in equation (1) denote positive and negative types of the current-controlled current conveyors (CCCII+ and CCCII-) respectively. RX represents the intrinsic series input resistance of the conveyor at X port, which is electronically tunable via I0. In the case of CMOS based CCCII, it is defined as [15]

Index Terms― CCCII, Oscillator, Gain control

I. INTRODUCTION Current conveyor received attention in recent years as an alternative to the voltage mode operational amplifiers. When arranged with other electronic elements can be used for the implementation of various functions operating either in the voltage-mode or current-mode [1]. Current conveyor offers many advantages over conventional operational amplifier circuits such as provide higher voltage gain over a large signal bandwidth results large gain-bandwidth- product, wider dynamic range, and low power consumption [1]. Over the last two decades or so several schemes of design of R-C oscillator based on various current conveyors have been developed [2-16]. Most of the reported oscillators provide non-interacting controls over the condition of oscillation and frequency of oscillation. There are different techniques of amplitude control from simple nonlinear limiters [17] to sophisticated control loops which require complicated circuitry on the loop than the primary oscillator [18]. In this paper a CCCII based oscillator circuit with output amplitude control is proposed. The CCCII based current mode oscillator circuit [8] consists of two CCCII and two grounded capacitors. One CCCII+ is added at the output port of this oscillator circuit which is used to control the amplitude of the oscillator electronically and at the same time it functions as a buffer to avoid any loading effect.

Rx 

gm2

1  g m4

g m i  2β i I 0 βi 

(2)

(i  2,4)

ε 0 ε ins µ i Wi t ox L i

(3)

(4)

The CCCII based current mode oscillator circuit with gain control is shown in fig. 2. The routine analysis yields the characteristic equation [8] as s2Rx1Rx2C1C2 + (Rx1C1 + Rx2C2 -- Rx1C2)s + 2 = 0 (5)

II. CIRCUIT DESCRIPTION The symbol of analog building block CCCII is shown in Fig. 1. The port relationships of CCCII are given in matrix form in (1).

Figure 2. CCCII based oscillator circuit with gain control

The frequency of oscillation is obtained as

ω0  Figure 1. Block diagram for CCCII

142

2 2R X1R X2 C1C 2

(6)

Poster Paper Proc. of Int. Colloquiums on Computer Electronics Electrical Mechanical and Civil 2011

R X1  2R X2

(7)

and the condition of oscillation assuming C2 = 2C1 is From equations (2), (3), (4) and (7) the oscillation condition is obtained as I02 = 4I01 (8) Further analysis gives output of the oscillator as

I out 

VY3 R X3

(9)

Figure 3. Oscillation obtained with I 01 =50µA I 02=200µA and I03 =100µA

Equations (6) and (9) reveal that the frequency of oscillator can be varied electronically with bias currents I01 and I02 without disturbing the amplitude of the output signal. Similarly, the amplitude of the output signal can be varied electronically with I03 without disturbing the frequency of oscillation. It may also be noted that the current output is obtained at high impedance output port. Hence the circuit is suitable for cascading without any additional buffer. ΙΙΙ. SIMULATION & RESULT The proposed gain control oscillator circuit has been simulated using the CMOS based CCCII circuit given in [15]. The parameters of the AMS 0.35µm CMOS technology are used for all MOSFETs in the circuit. The dimensions of the NMOS and PMOS transistors used in this circuit are given in Table 1[15].

Figure 4. Input current waveform in I 03

Figure 5. The amplitude modulated wave form for I 03

The power supplies for the CCCII± are taken as ±2.5V. The capacitor values are taken as C1=10nF and C2=24nF. Theoretically C2=2C1, but due to non-ideal behavior of the CCCII±, the oscillation is obtained at slightly deviated value of C2. Output of the oscillator at I01=50µA, I02=200µA and I03=100µA is shown in Fig.3. To show the electronic controllability of amplitude of oscillator a triangular wave of amplitude 400µA, as shown in Fig.4, is applied at I03 of the oscillator circuit. The corresponding amplitude modulated output of the oscillator is shown in Fig.5. It is found that the amplitude of the output current is varying according to the variation of bias current I03. Fig.6 shows the variation of percentage total harmonic distortion (% THD), which is well within the acceptable limit.

Figure 6. Variation of %THD vs bias current (I 03 )

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Poster Paper Proc. of Int. Colloquiums on Computer Electronics Electrical Mechanical and Civil 2011

CONCLUSION

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An oscillator with gain control mechanism is proposed. The simulated result verifies that the proposed circuit can offer electronic tunability to amplitude of oscillation and frequency of oscillation. REFERENCES [1] C. Toumazou, F. J. Lidgey, D. G. Haigh, “Analogue IC design: The current mode approach” IEE circuit and system series 2, Peter Peregrinus, 1990. [2] M. T. Abuelma’atti, A. A. Al-Ghumaiz, “Novel CCI- based single element controlled oscillators employing grounded resistors and capacitors”, IEEE transaction on circuit and system, vol 43, pp 153-155, 1996. [3] Abhirup Lahiri, “ Deriving (MO)(I) CCCII based second-order sinusoidal oscillators with non-interactive tuning laws using state variable method”, Radioengineering,vol.20, pp 349-354, 2011. [4] Mohd Yusuf Yasin, Bal Gopal, “High frequency oscillator design using a single 45nm CMOS current controlled current conveyor (CCCII+) with minimum passive components”, Circuits and systems, vol 2, pp 53-59, 2011. [5] M. T. Abuelma’atti, A. A. Al-Ghumaiz, M. H. Khan, “Novel CCII based single element controlled oscillators employing grounded resistors and capacitors”, Int. J. Electron. Vol 78, pp 1107-1112, 1995. [6] R. Nandi, “Precise insensitive tunable RC-oscillator realisation using current conveyors”, proceedings of institution of electrical engineers, pt G, vol 133, pp 129-132, 1986. [7] J. W. Horong, C. W. Chang, M. H. Lee, “Single element controlled sinusoidal oscillators based on CCIIs (-IR)”, Int. J. Electron. Vol 6, pp 831-836, 1997a. [8] N. Pandey, S.K.Paul, “A novel electronically tunable sinusoidal oscillator based on CCCII (-IR)”, J. of Active and Passive Electronic Devices, vol 13, pp 1-7, 2008.

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