Active-only current-mode first-order allpass filter and its application in quadrature oscillator

Transcription

1 ndian Journal of Pure & Applied Physics Vol. 53, Auust 2015, pp Active-only current-mode first-order allpass filter and its application in quadrature illator Adirek Jantakun 1 * & inai Jaikla 2 1 Department of Electronics and Telecommunication Enineerin, Faculty of Enineerin Rajamanala University of Technoloy san, Khonkaen Campus, Khonkaen 40000, Thailand 2 Department of Enineerin Education, Faculty of ndustrial Education, Kin Monkut's nstitute of Technoloy adkraban ankok 10520, Thailand * mr.adirek@hotmail.com, winai.ja@hotmail.com Received 14 July 2013; revised 30 May 2014; accepted 16 December 2014 The current-mode first-order allpass filter (APF) usin only the active elements has been studied in the present paper. The proposed circuit comprises two operational transconductance amplifiers (OTAs) and one operational amplifier (OA) which is suitable to future development into an interated circuit. The pole frequency and phase response can be electronically adjusted with chanin the dc bias currents of OTAs. The APF has hih output impedance, which is easy to cascade in hih-order filter or drive load without usin a bufferin device. The current-mode quadrature illator is included to show the usability of the proposed filter. The results of PSPCE simulation are accordant with the theoretical analysis. Keywords: Active-only APF, First-order allpass filter, Current-mode, Operational transconductance amplifiers, Operational amplifier 1 ntroduction The current-mode circuits have been found widely in analo sinal processin circuits 1 ; for example current-mode biquadratic filter, quadrature illator, inductance simulator, multiphase sinusoidal illator etc, due to its advantaes in term of inherently wide bandwidth, hiher slew-rate, reater linearity, wider dynamic rane, simple circuitry and low power consumption 1-4. Mostly, the pole-model of the Operational amplifier (OA) has been used in the place of external capacitors 5-10, which is suitable for fabricatin in monolithic chip The Operational Transconductance Amplifier (OTA) seems to be a versatile component in the realization of a class of analo sinal processin circuits, especially analoue frequency filters. n addition, the output current of OTA can be electronically adjusted. These are advantaes for motivatin the circuit desiners to develop filters and illator usin only the OAs and OTAs Firstorder allpass filter (APF) or phase-shifter circuits are extremely useful in electronics and electrical enineerin such as in modulatin and demodulin systems, quadrature illator, multiphase illator and hih Q band pass filter From literature survey, it is found that several implementations of first-order APF usin different hih performances active buildin block have been reported Unfortunately, these reported circuits suffer from one or more of followin weaknesses. The excessively use 12,13,18,19,23,25 of the passive elements is not convenient to further fabricate C and cannot provide electronic tenability. The reported circuits 26,27 enjoy sinle active element and electronic tunin by adjusted transconductance ain but they require multiple current output terminals (z and x port). Consequently, these circuits become more complicated. Moreover, the circuits in Refs (12,13, 15-20, 22,23, 25) use external passive resistors, which are not ideal for interation 27. The circuit specifications of these reported APFs are compared with the proposed APF as presented in Table 1. The current-mode first-order allpass filter is proposed, emphasizin on the use of an active element without external passive components. t employs 1 OA and 2 OTAs, which are suitable for fabricatin in monolithic chip. To verify the workability of the proposed circuit, the PSPCE simulation results of a CMOS implementation and its application of the allpass filter as a quadrature illator have been included.

2 558 NDAN J PURE & APP PHYS, VO 53, AUGUST 2015 Ref 2 Principle and Operation Active element 2.1 Operational Transconductance Amplifier A brief review of the OTA is iven. Generally, the OTA has infinite input and output impedances. The output current of an OTA is iven by: Table 1 Comparison between various APFs Number of active element Number of R+C Electronic tune Matchin Condition Current-mode output [11] VDA Yes No No [12] CC No Yes Yes [13] CC No Yes Yes [14] ZC-CTA Yes No Yes [15] DVCCTA Yes No No [16] DTA Yes No Yes [17] DTA Yes No No [18] CC No No No [19] CC No Yes Yes [20] OTA Yes Yes Yes [21] OTA Yes Yes Yes [22] OTA Yes Yes Yes [23] DVCC+OTA Yes No Yes [24] CCCCTA Yes No Yes [25] FDCC No No Yes [26] CDTA Yes No Yes [27] ZC-CFTA Yes No Yes Proposed APF OTA+OA Yes No Yes ( ) O m V+ V, (1) Fi. 1 OTA (a) Symbol (b) Equivalent circuit where m is the transconductance ain of the OTA. For a CMOS OTA, the transconductance ain can be expressed by: m k. (2) where k µ Cox ( / ) is the physical parameter of CMOS transistor. The symbol and the equivalent circuit of the OTA are shown in Fi. 1(a and b), respectively. 2.2 Operational Amplifier The open-loop ain of the operational amplifier 5-10 is approximately iven by: A, (3) s where is the ain-bandwidth product. Fi. 2 Proposed current-mode first-order APF 2.3 Proposed Current-mode First-order Allpass Filter The proposed active-only current-mode first-order APF filter is shown in Fi. 2. t consists of 2 OTAs and 1 OA which is suitable for fabricatin in monolithic chip for use in portable electronics

3 JANTAKUN & JAKA: CURRENT-MODE FRST-ORDER APASS FTER 559 equipments. From the OTA and OA properties, the followin current transfer function is subsequently obtained s Out in s + m2 m1 m2 m1. (4) From Eq.(4), the pole frequency, current ain and phase response of the proposed current-mode firstorder APF circuit are: m2 0, (5) m 1 Out G( ) 1, (6) and in 1 m 1 φ( ) 180 2tan. (7) m2 Substitutin the transconductance m as iven in Eq. (2) into Eqs (5) and (7), the pole frequency and phase response of the proposed circuit are iven by: 2 0, (8) 1 and 1 1 φ( 0 ) tan. (9) 2 t is clear that the pole frequency and phase response of the proposed current-mode first-order APF can be electronically adjusted by either 1 or 2. n addition, the output-current port is of hihimpedance which is easy to drive a load without usin a bufferin device. 2.4 Proposed Current-mode Quadrature Oscillator The proposed first-order APF is used to desin a current-mode quadrature illator by cascadin a non-invertin and an invertin APF as shown in Fi. 3. The characteristic equation of the currentmode quadrature illator (assumin 1 2 ), can be obtained: s + 0. (10) 2 m2 m4 2 m3 m1 From Eq.(10), the illation frequency ( be concluded to be: ) can m2 m4. (11) m1 m3 Substitutin the transconductance m as iven in Eq. (2) into Eq. (11), the illation frequency ( ) is iven by: Fi. 3 Proposed current-mode quadrature illator (12) t is obviously found from Eq. (12), the illation frequency can be electronically adjusted by settin 1, 2, 3 or Analysis of the Non-idealities of OA and OTA For a complete analysis of the circuit, it is necessary to take into account the non-idealities of the OA and OTA on the transfer function of proposed current-mode first-order APF circuit. The parasitic pole of the OA and OTA for the open loop ain A( s ) and transconductance ain ( s ) are presented 5-10 by: i2 i Ani s( s + ) 2i m (13)

4 560 NDAN J PURE & APP PHYS, VO 53, AUGUST 2015 mnj mjj, ( j 1, 2 ) (14) s + j where 2i and j denote the second pole of the OA and the first pole of OTA, respectively. The Ani ( s ) and ( s ) can be assumed 5-10 as: mnj i Ani (1 τ is), (15) s (1 µ s), (16) mnj mj j where τ i 1/ 2i and µ j 1/ j Usin Eqs (15) and (16) and reanalysis of the proposed current-mode first-order APF circuit (assumin OTA 1 and OTA 2 are of same ability, that µ µ ), the current transfer function of Fi. 2 is 1 2 becomes: m2 s Out m 1 + m2τ, (17) in m2 s + + τ m1 m2 t is found from Eq. (17) that the current ain is equal to unit. The pole frequency and phase response of the proposed circuit are expressed as: m2 0, (18) + τ and m1 m2 φ( ) tan ( τ ) +. (19) 1 m1 m2 m2 Then, the illation frequency of the current-mode quadrature illator shown in Fi. 3 is chaned to: m2 m4 1 2 ( + τ )( + τ ) m1 m2 1 m3 m4 2. (20) 3 Simulation Results To prove the performances of the proposed currentmode first-order APF circuit, the PSPCE simulation was performed for examination. Fiure 4 shows the Fi. 4 Schematic of CMOS (a) OA (b) OTA Table 2 Aspect transistor ratio of the CMOS OA M 1, M M M 3, M M M M Table 3 Aspect transistor ratio of the CMOS OTA M 1, M M 5, M M 3, M M 9,M M 6, M M 10,M schematic description of the CMOS OTA and CMOS OA 28 used in the simulations. The parameters of the NMOS and PMOS transistor are a 0.25m TSMC CMOS technoloy 28 with ±2 supply voltaes. The CMOS OA used C 1 30 pf with bias voltaes V 1 1 V and V V. The aspect transistor ratios of CMOS OA and OTA are listed in Tables 2 and 3, respectively. These transistor ratios are taken from Ref. 28. The bandwidth of CMOS OA is shown in Fi. 5. t is found that the-3d frequency is 2.06 MHz. Fiure. 6 shows the transconductance value where is varied from 1 µa-500 µa. The result in Fi. 7 shows the ain and phase responses of the proposed current-mode APF where µa. t is evident that the pole frequency is about 2.05 MHz,

5 JANTAKUN & JAKA: CURRENT-MODE FRST-ORDER APASS FTER 561 Fi. 5 Frequency response of the CMOS OA Fi. 9 Time-domain response of the APF at a 2.06 MHz sinusoidal input sinal Fi. 6 Transconductance value of the CMOS OTA relative to Fi. 7 Gain and phase response of the proposed current-mode first-order APF Fi. 10 Relative between manitudes of input and output Fi. 8 Phase response of the APF for different value of 2 that is in correspondence with the theoretical value of 2.06 MHz. The error of the pole frequency stems from the non-ideal parameters is displayed. The electronic tunability of allpass filter is shown in Fi. 8. n this case, the bias current 2 is varied to 50 µa, 100 µa and 200 µa, respectively. To illustrate the time-domain performance of the proposed APF, the result is shown in Fi. 9. The input sinal is a sinusoidal sinal with 2.06 MHz and peakto-peak values of 160 µa, where µa. The phase shift anle of output sinal is about The Fi. 11 Output currents for difference values of 2 issajous pattern in Fi. 10 shows the relative between manitudes of input and output sinals. The output currents for difference values of dc bias current 2 are shown in Fi. 11. t is seen that the phase shift can be electronically tuned as expressed in Eq. (9). The total harmonic distortion (THD) of sinusoidal output sinal of 2.06 MHz with respect to peak-topeak amplitude of sinusoidal input sinal is shown in Fi. 12. The minimum of THD values is 0.58% with 160 µa peak-to-peak amplitude.

6 562 NDAN J PURE & APP PHYS, VO 53, AUGUST 2015 for use in portable electronics equipments such as mobile communication systems or wireless communication devices. The pole frequency and phase response of APF can be adjusted with electronic tunin by dc bias currents of OTAs. Moreover, the output current of APF has hih output impedance which facilitates cascadin in currentmode confiuration. Moreover, an application as current-mode quadrature illator by cascadin APF is produced. The current-mode first-order APF and current-mode quadrature illator are verified throuh PSPCE simulations usin 0.25m TSMC CMOS parameters. The simulation results aree well with the theoretical anticipation. Fi. 12 THD variation versus peak-to-peak amplitude of the applied sinusoidal input current Fi. 13 Output waveforms of quadrature illator Fi. 14 Output spectrum of quadrature illator Fiure 13 shows the simulated output waveforms of the current-mode quadrature illator in Fi. 3, where the bias currents µa. The illation frequency is found to be 1.98MHz which is closed to the theoretical value (2.06MHz). Fiure 14 shows the simulated output spectrum, where the total harmonic distortion (THD) is about 3.78% 4 Conclusions An electronically adjustable current-mode firstorder allpass filter (APF) has been presented. t employs only the active elements, 2 OTAs and 1 OA, which are suitable for fabricatin in monolithic chip References 1 Alpaslan H & Yuce E, ndian J Pure & Appl Phys, 51 (2013) Jaikla, Siripruchayanun M, iolek D & ajer J, Radioenineerin, 17 (2008), Jantakun A & Jaikla, Turk J Elec En & Comp Sci, 21 (2013) iolek D, Keskin A Ü & iolkova V, EE Proc-Circuits Devices Syst, 4 (2010) Minaei S, Cicekolu O, Kuntman H & Turkoz S, nt J of Electronics, 89 (2002) Tsukutani T, Hiashimura M, Sumi Y & Fukui Y, nt J of Electronics, 87 (2000) Minaei S, Topcu G & Cicekolu O, nt J of Electronics, 92 (2005) Minaei S, Topcu G & Cicekolu O, nt J of Electronics, 90 (2003) Tsukutani T, Hiashimura M, Takahashi N, Sumi Y & Fukui Y, nt J of Electronics, 88 (2001) Shah N A, Rather M F & qbal S Z, J of Active and Passive Electronic Devices, 1 (2006) Herencsar N, Minaei S, Koton J, Yuce E & Vrba K, Analo nter Circ Si Process., 74 (2013) Hiashimura M & Fukui Y, EEE Trans. Circuit and System, 37 (1990) Horn J, Hou C, Chan C M, Chun Y, iu H, & in C T, nt J of Electronics, 93 (2006) iolek D & iolkova V, Electronics ettes, 45 (2011) Pandey N Pandey R & Paul S K, J of Electron Devices, 12 (2012) Vavra J, ajer J & iolek D, Proceedins of 35th nternational Conference on Telecommunications and Sinal Processin (TSP), (2012) Herencsar N, Koton J, Vrba K & Metin., Proceedins of 35th nternational Conference on Telecommunications and Sinal Processin (TSP), (2012) Horn J, Computers and Electrical Enineerin, 31 (2005) Un M & Kacar F, J of Electrical and Electronics Enineerin, 8(1) (2008) Al-Hashim, Dudek F & Sun Y, Analo nterated Circuits and Sinal Processin, 24(2) (2000) 163.

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