Electronically-Controlled Current-Mode Second Order Sinusoidal Oscillators Using MO-OTAs and Grounded Capacitors

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1 Circuits and Systems, 20, 2, 6573 doi:0.4236/cs Published Online April 20 ( ElectronicallyControlled CurrentMode Second Order Sinusoidal Oscillators Usin MOOTAs and Grounded Capacitors Data Ram Bhaskar, Kasim Karam Abdalla, Raj Senani 2 Department of Electronics and Communication Enineerin, Faculty of Enineerin and Technoloy, Jamia Millia Islmia, New Delhi, India 2 Division of Electronics and Communication Enineerin, Netaji Subhas Institute of Technoloy, Delhi, India senani@nsit.ac.in Received December 7, 200; revised February 9, 20; accepted February 2, 20 Abstract Five new electronicallycontrollable second order currentmode sinusoidal oscillators usin three multioutput operational transconductance amplifiers (MOOTAs) and two rounded capacitors (GC) have been presented. Simulation results are included to confirm the theoretical analysis based upon CMOS OTAs implementable in 0.5 µm technoloy. Keywords: Oscillators, Analo Electronics, Current Mode Circuits, Operational Transconductance Amplifiers. Introduction Recently, Tsukutani, Sumi and Fukui [] presented two currentmode OTAC sinusoidal oscillators each of which employs three MOOTAs and three rounded capacitors (GC) and provides three explicit current outputs. However, whereas one of the circuits of [] does not have independent controllability of the condition of oscillation (CO) and the frequency of oscillation (FO) throuh different transconductances (which is not only a desirable but also an expected property which one likes to see in any OTAC oscillator), on the other hand, both the circuits employ three GCs and hence, are not canonic. The main objective of this paper is to present five new currentmode electronicallycontrollable second order sinusoidal oscillators which use only three MOOTAs like the circuits of [] but in contrast to the circuits of [], the proposed circuits use no more than two GCs and are capable of providin a noninteractin and independent control of both CO and FO and in addition also provide quadrature outputs which find numerous applications (for instance, in communications for quadrature mixers and sinlesideband enerators and in instrumentation for vector enerator or selective voltmeters [2] etc.). 2. The Proposed Circuits The proposed circuits are shown in Fiure. For an ideal MOOTA with transconductance m, the current output I o is iven by I o = m (V V ), where V and V are the input voltaes at noninvertin input terminal and invertin input terminal respectively. Routine analysis yields, the condition of oscillation (CO) and the frequency of oscillation (FO) for all circuits as summarized in Table, which also shows the relevant modes of availability of quadrature outputs in all cases. From the expressions of FO iven in Table, it can be easily deduced that manitude of all active and passive sensitivities of FO, in all the five circuits, would be in the rane of 0 to /2 and circuits thus, enjoy low sensitivity properties. 3. Simulation Results To verify the validity of the proposed confiurations, circuit simulation of the oscillators has been carried out usin the CMOS MOOTA circuit from [] (presented here as Fiure 2). In PSPICE simulation, implementation was based upon a CMOS OTA in 0.5 µm technoloy. The aspect ratios of the MOSFETs were taken as shown in Table 2. The CMOS OTAs were biased with DC power supply voltaes V DD = 2.5 V, V SS = 2.5 V. The enerated waveforms, transient and the frequency spectrum for the proposed circuits obtained from simulations are shown in Fiure 3, Fiure 4 and Fiure 5,

2 66 D. R. BHASKAR ET AL. m2 m2 I o2 02 m3 m3 m m I o3 03 C I o0 C 2 2 m2 I o202 C I o0 m C 2 2 m3 I o303 m m I o I 0 m2 I o2 02 C I o2 02 m3 C I o2 02 I o 0 C (2) () m3 m3 m2 (3) m2 I o3 03 (4) I o303 C 2 2 C 2 m I o3 03 C 2 m I o 0 (5) Fiure. Proposed confiurations. respectively. The element values used in the simulations alon with the theoretical and practical output frequency and total harmonic distortions (THD) for the proposed circuits are summarized in Table 3. All the proposed oscillators have been checked for robustness usin MonteCarlo simulations, however, to conserve space, a sample result has been shown in Fiure 6 for the oscillator (5) of Fiure, which confirms that for 5% variations in the value of m3, the value of oscillation frequency remains close to its normal value of.996 MHz and hence almost unaffected by chane in m3 (which should be the case since m3 does not feature in the expression of FO). In all cases, a very ood correspondence between desined values and those observed from PSPICE simulations has been obtained. The simulation results, thus, confirm the workability of the proposed confiurations. 4. Comparison with Other Previously Known OTABased Oscillators It is now useful to compare the proposed new circuits with some of the earlier proposed OTAbased oscillators. Recently, Kamat, Anand Mohan and Prabhu [3] presented a quadrature oscillator employin two MOOTAs, two sinle output OTAs and two GCs. The circuit does not have independent controllability of CO and FO. It may also be recalled in this context that much earlier, in reference [4], two minimumcomponent electronicallytunable sinusoidal oscillators usin two OTAs and two GCs had been presented however, these circuits too did not have independent controllability of CO and FO. Furthermore, there is another class of OTAbased RC oscillators known earlier [59] which employ one or two OTAs alon with a number of resistors and two capacitors. However, when these OTARC oscillators from [59] can be transformed into OTAC oscillators, by simulatin the resistors with OTAs, the resultin entirelyotabased oscillators will

3 D. R. BHASKAR ET AL. 67 V DD V DD M 9 M M 3 M 4 5 M 6 M 0 I I o V in M M V in 2 in in I o o I I bias M 7 M 8 M M 2 Fiure 2. MOOTA. V SS SS Table. Condition of oscillation and frequency of oscillation for the proposed circuits. Circuit No. Condition of Oscillation (CO) ( m3 m ) 0 2 ( m2 m ) 0 3 ( m m2 ) 0 4 (C 2 m3 C m ) 0 5 ( m2 m3 ) 0 Frequency of Oscillation (FO) mm2 CC 2 m2m3 CC 2 m2m3 CC 2 mm2 CC 2 mm2 CC 2 Availability of Quadrature Outputs Io2 s m2 Io2 s m m2, Io s sc2 Io3 s m3sc2 Io3 s m3 Io3 s m3, for m = m2 Io s sc Ios sc Io3 s m3 Io3, s m3 for m = m2 Io s sc Ios sc Io s m Ios sc Io s m2m Io s m, Io3 s m3sc Ios sc Table 2. Aspect ratios of MOSFETs used in the MOOTA implementation. MOSFET W(µm) L(µm) M, M M 3, M 4, M 5, M 6, M 9, M M 7, M 8, M, M not remain as efficient and practically viable due to the requirement of an excessive number of OTAs. In comparison, the new circuits are free from above mentioned deficiencies of the circuits presented earlier in [39]. 5. Concludin Remarks Five new currentmode electronically controllable OTAC sinusoidal oscillators have been presented. Like the recently proposed circuits of [], the proposed circuits also employ only three MOOTAs and rounded capacitors as preferred for IC fabrication [0] and []. However, by contrast to the circuits presented in [] both of which require three capacitors and hence are noncanonic, the proposed circuits require only two capacitors and hence, are canonic. All the proposed circuits enjoy the feature of independent controllability of oscillation frequency and condition of oscillation, which is not available in one of the circuits presented in []. The new circuits are also free from the drawbacks of the circuits presented earlier in [39]. Also, all the proposed circuits provide quadrature outputs as an additional feature not available in the circuits of []. The active and passivesensitivities of all the circuits are very low. The workability

4 68 D. R. BHASKAR ET AL. (a) (b) (c) (d)

5 D. R. BHASKAR ET AL. 69 (e) Fiure 3. Output waveforms of (a) circuit (b) circuit 2 (c) circuit 3 (d) circuit 4 (e) circuit 5. (a) (b) (c)

6 70 D. R. BHASKAR ET AL. (d) (e) Fiure 4. Output transient of (a) circuit (b) circuit 2 (c) circuit 3 (d) circuit 4 (e) circuit 5. (a) (b)

7 D. R. BHASKAR ET AL. 7 (c) (d) (e) Fiure 5. Frequency spectrum of (a) circuit (b) circuit 2 (c) circuit 3 (d) circuit 4 (e) circuit 5. of the proposed circuits has been demonstrated by SPICE simulation results. The transconductance of an OTA is temperature dependent this calls for appropriate temperature compensation for which numbers of schemes are known in the literature [24]. However, the study of modified versions of the proposed circuits incorporatin temperature compensation would require considerable additional work; therefore, it was considered to be outside the scope of present work. Lastly, it may be mentioned that the

8 72 D. R. BHASKAR ET AL. Fiure 6. Result of the MonteCarlo Simulation of oscillator circuit (5) of Fiure. Circuit No. m (ma/v) Table 3. The values of the capacitors and transconductances for various oscillators. I b (ma) m2 (ma/v) I b2 (ma) m3 (ma/v) I b3 (ma) C (nf) C 2 (nf) F Theoretical (MHz) F Practical (MHz) % % % % % THD circuits proposed in this paper are inspired by the ideas contained in [59]. 6. References [] T. Tsukutani, Y. Sumi and Y. Fukui, Electronically Controlled CurrentMode Oscillators Usin MOOTAs and Grounded Capacitors, Frequenz, Vol. 60, No. 2, 2006, pp doi:0.55/freq [2] W. Tansrirat, Current Differencin Transconductance AmplifierBased CurrentMode FourPhase Quadrature Oscillator, Indian Journal of Enineerin and Material Sciences, Vol. 4, No. 4, 2007, pp [3] D. V. Kamat, P. V. A. Mohan and K. G. Prabhu, Novel FirstOrder and SecondOrder CurrentMode Filters Usin MultipleOutput Operational Amplifiers, Circuits Syst Sinal Process, Vol. 29, No. 3, 200, pp doi:0.007/s y [4] M. T. Abuelma atti, New Minimum Componet Electronically Tunable OTAC Sinusoidal Oscillators, Electronics Letters, Vol. 25, No. 7,989, pp. 45. doi:0.049/el: [5] M. T. Abuelma atti and M. H. Khan, Grounded Capacitor Oscillators Usin a Sinle Operationl Transconductance Amplifier, Active and Passive Electronic Components, Vol. 9, No. 2, 996, pp [6] Y. Tao and J. K. Fidler, Generation of SecondOrder SinleOTA RC Oscillators, IEE Proceedins of Circuits Devices Systems, Vol. 45, No. 4, 998, pp doi:0.049/ipcds: [7] Y. Tao and J. K. Fidler, Electronically Tunable DualOTA SecondOrder Sinusoidal Oscillator/Filters with Noninteractin Controls: A Systematic Synthesis Approach, IEEE Transactions on Circuits Systems I, Vol. 47, No. 2, 2000, pp [8] V. Sinh, Equivalent Forms of DualOTA RC Oscillators with Application to GroundedCapacitor Oscillators, IEE Proceedins of Circuits Devices Systems, Vol. 53, No. 2, 2006, pp doi:0.049/ipcds: [9] V. Sinh, Equivalent Forms of SinleOperational Transconductance Amplifier RC Oscillators with Application to GroundedCapacitor Oscillators, IET Circuits Devices Systems, Vol. 4, No. 2, 200, pp doi:0.049/ietcds [0] B. Bhushan and R. W. Newcomb, Groundin of Capacitors in Interated Circuits, Electronics Letters, Vol. 3, No. 4, 967, pp doi:0.049/el:96704 [] R. Senani, Realization of a Class of Analo Sinal Processin/Sinal Generation Circuits: Novel Confiura

9 D. R. BHASKAR ET AL. 73 tion Usin CurrentFeedback OpAmps, Frequenz, Vol. 52, No. 90, 998, pp doi:0.55/freq [2] H. S. Malvar and M. Luetten, Temperature Compensation of OTABased Filters and Multipliers, Electronics Letters, Vol. 23, No. 7, 987, pp doi:0.049/el: [3] W.S. Chun, H.W. Cha and K.H. Kim, Temperature Stable VCO Based on Operational Transconductance Amplifiers, Electronics Letters, Vol. 26, No. 22, 990, pp doi:0.049/el: [4] C. A. Karybakas, C. Kosmatopoulos and T. Laopoulos, Improved Temperature Compensation of OTAs, Electronics Letters, Vol. 28, No. 8, 992, pp doi:0.049/el: [5] R. Senani, M. P. Tripathi, D. R. Bhaskar and A. K. Banerjee, Systematic Generation of OTAC Sinusoidal Oscillators, Electronics Letters, Vol. 26, No. 8, 990, pp doi:0.049/el: [6] D. R. Bhaskar, M. P. Tripathi and R. Senani, A Class of ThreeOTATwoCapacitor Oscillators with Noninteractin Controls, International Journal of Electronics, Vol. 74, No. 3, 993, pp doi:0.080/ [7] D. R. Bhaskar, M. P. Tripathi and R. Senani, Systematic Derivation of All Possible Canonic OTAC Sinusoidal Oscillators, Journal of the Franklin Institute, Vol. 330, No. 5, 993, pp doi:0.06/ (93) [8] R. Senani, New Electronically Tunable OTAC Sinusoidal Oscillator, Electronics Letters, Vol. 25, No. 4, 989, pp doi:0.049/el: [9] M. T. Abuelma atti, Two New Interable ActiveC OTABased Voltae (Current) Controlled Oscillators, International Journal of Electronics, Vol. 66, No., 989, pp doi:0.080/