VOLTAGE DIFFERENCING TRANSCONDUCTANCE AMPLIFIERS BASED MIXED-MODE QUADRATURE OSCILLATOR

Transcription

1 Rev. Roum. Sci. Techn. Électrotechn. et Énerg. Vol. 6 pp Bucarest 6 VOLTAGE DIFFERENCING TRANSCONDUCTANCE AMPLIFIERS BASED MIXED-MODE QUADRATURE OSCILLATOR ADIREK JANTAKUN Key words: Quadrature oscillator Voltage differencing transconductance amplifier (VDTA) Grounded capacitor. This article presents two circuits of mixed-mode quadrature oscillator based-on voltage differencing transconductance amplifier (VDTA). The circuits consist of two VDTAs two grounded capacitors. The quadrature outputs both voltage-mode current-mode are studied. The high-impedance output current which is connected easily to load or next stages circuit the amplitude can be electronically adjusted with the dc bias current. In addition the grounded capacitors were well-done for integral circuits (IC) implementation. The condition of oscillation (CO) frequency of oscillation (FO) can be electronically/orthogonally controlled by tuning the dc bias currents. The results of PSPICE simulation are accordant with the theoretical analysis. Moreover the proposed circuit can operate at very low voltage of ±.5 V only.33 mw of power dissipation.. INTRODUCTION Well-known that quadrature oscillator (QO) or sinusoidal oscillator provides 9 degree phase difference. It is vastly used in electrical or electronic engineering such as the modulation demodulation circuits of communication system instrument or measurement system control system in laboratory of communication systems [ 4]. Currently the passive elements in analogue signal processing circuits are frequently connected to ground. Especially the grounded capacitor is connected at high-impedance ports which is advantage for integrated circuit implementation [4]. The grounded capacitor serves as compensation or elimination the latent capacity that occurs at the terminals of the active device the nodes of the circuit [ 6]. An adjustment of the amplitude of sinusoidal signal is attractive to research development [5 6] since it can be applied to the communication systems. These are amplitude modulation (AM) / amplitude shift keying (ASK) which are classical modulation in the communication system. Furthermore AM is useful in plenty applications such as AM radio broadcasting aircraft navigation system. Moreover ASK also is widely-used in many applications; for example in optical communication [5 6]. Especially an AM ASK are vastly used in laboratories for studying fundamental of electronics/telecommunication engineering. The QO based-on VDTA have been reported in the literature [7 3]. For example the oscillator circuits in [7 9] are compacted it can be tuned the condition of oscillation (CO) frequency of oscillation (FO) with electronic method by dc bias current of VDTA. However they are afflicted from using an external passive resistor may occur the thermal noise difficult to implementation in IC []. The CO FO have been presented in [] which are easily electronically adjusted by tuning the dc bias current of VDTA. Notwithsting it resists of two types of active device which are from differential different current conveyor (or DDCC) VDTA excessive passive elements including three grounded capacitors one grounded resistor. The circuit in [] employed of two grounded capacitors which is ideal for IC implementation. Also it can be electronically/independently adjusted the CO FO. Unfortunately the output currents are unfeasible for adjustment of the amplitude which is not convenient in AM/ASK systems. The circuits presented in [] obtained current-mode QO it can be tuned the FO CO with dc bias current of VDTAs. Nonetheless the circuit from the output currents still cannot electronically be controlled the amplitude uses three grounded capacitors. The current-mode sinusoidal oscillator in [3] introduced the FO CO which can be electronically adjusted by dc bias currents as well as the amplitude can be tuned with biasing of VDTA which is good for AM/ASK communication system. Nevertheless the output current is not quadrature signal the circuit is used of three grounded capacitors. The purpose of this paper is to introduce the synthesis of QO circuits based-on VDTAs. The usefulness of proposed circuits have following as: Using grounded capacitors which are suitable for IC implementation eliminable the parasitic capacitances at ports/nodes.the CO FO can easily be electronically/ orthogonally controlled via dc bias current of VDTAs. The quadrature output signals provide voltage-mode current-mode. The output currents have high output impedances that useful for current-mode circuitry configuration. The amplitude of output current can be electronically adjusted with dc bias current which is suitable for using in AM/ASK systems.. DESCRIPTION OF VDTA Voltage differencing transconductance amplifier (or VDTA) has been introduced by Biolek et al. [4]. The symbol of VDTA is displayed in Fig.. It can be seen that p n are voltage input terminals the output currents terminals are z z x x. Also all terminals of VDTA are high-impedances [5]. The ideal characteristics of voltage current of VDTA are derived in the following equation: I z I z I x I x V p Vn. () Vz V z Rajamangala University of Technology Isan Department of Electronics Telecommunication Engineering Faculty of Engineering Khonkaen Campus Khonkaen Thail 4; mr.adirek@hotmail.com

2 Mixed-mode quadrature oscillator 69 Fig. The electrical symbol of VDTA. Fig. CMOS implementation of VDTA [6]. From Eq. () it can be seen that the first transconductance g mf second transconductance g ms of VDTA can be tuned electronically by the external dc bias currents [5]. Yesil et al. [6] has been presented the new simple CMOS of VDTA which is shown in Fig.. It consists of two Arbel-Goldminz transconductances [7]. The g mf g ms of VDTA can be approximated as follows: ki BF () ki BS (3) where W k μ COX μ is the mobility of the carrier of L CMOS (NMOS PMOS) transistors C OX is the gateoxide capacitance per unit area W L are the channel width length respectively. The I BF I BS control adjust the currents of the transconductance g mf g ms of the VDTA respectively. 3. PROPOSED QO CIRCUITS The realization of QO circuits are displayed in Fig. 3a b. They are comprises with two VDTAs two grounded capacitors. The grounded capacitors are suitable for IC architecture which is reduced the area of IC implementation as well as compensating/eliminating the parasitic capacitances at input/output ports of VDTAs nodes of circuit [ 6]. The circuits in Fig. 3 analyzed by using equation () the characteristic equation can be expressed as: s CC + s( ) C + (4 s CC + s( ) C +. (4 Fig. 3 Proposed quadrature oscillator circuits. From (4 (4 that are characteristic equations of QO circuits for Fig. 3a b respectively. Therefore the two QO circuits will be produced the quadrature signals when the CO is succeed: g (5) mf when the CO is succeed the two QO circuits will be produced the oscillation with frequency of ωosc CC. (6) Note that two circuits of QO have the same features. It is observed that both CO FO can easily be electronically adjusted with dc bias current of VDTAs. Thus the CO can be adjusted by tuning the dc currents bias of I BS I BF. Also the FO of two circuits are the same can be tuned with electronic tuning without influence of CO by I BF. In addition the quadrature output signals constrain of voltage-mode including V O V O current-mode denoted by I O I O. The output currents have highimpedance which can directly drive loads without external buffer devices [ 3 6]. For the quadrature voltage signals there are required the external voltage buffers to be used for connecting to a low impedance load or cascading to the next stages. Particularly the amplitude of output current I O can be electronically adjusted by I BS. If I BS is an information signal the output current I O will be generated AM/ASK signals. The proposed circuits can be easy used in AM/ASK communication systems [5 6] demonstrated in laboratories for studying the fundamental of electronics telecommunication engineering. In this way the amplitude of I O is given as I. (7) O Vz The phase relation between output signals of the proposed circuit which is shown in Fig. 3a. Those relation can be given as:

3 7 Adirek Jantakun 3 VO VO j9 e VO sc VO C IO IO j9 e IO( sc IO C (8) (8). (9) Then the CO can be obtained as ( CG A BβS+ CG B Aβ S) ( CGβ g + CGβ g ) A B F mf B A F mf (4) the FO can be rewritten as βsβ F ω osc (5) CACBβS CACBβF Fig. 4 The non-ideal VDTA. Similarly the phase relation of output signals in Fig. 3b can be shown follows: VO VO j9 e VO( sc VO C IO IO j9 e IO( sc IO C (). () It can be seen that from (8) () the output signals are 9 phase shifted. 4. NON-IDEAL ANALYSIS The relative of voltage current of VDTA for nonideal characteristic presented by Satansup et al. [5] which can then be obtained as follows equations I z βf I z βf I x I x βf βf βs βs Vp Vn () Vz V z where β F β S are the tracking errors of voltage for the first the second stages of VDTA. The impact of parasitic resistances parasitic capacitances which are appeared parallel at high-impedance ports of VDTA must be considered in the proposed circuits. These parasitic elements are demonstrated in Fig. 4. Considering the tracking errors parasitic elements the characteristic equation of the proposed circuits is shown in Fig. 3a the reanalysis is: s { C C β g C C β g } + + s{( C G g + C G g ) ( C G g + C G g )} + + β A B S ms A B F mf A BβS ms B AβS ms A BβF mf B AβF mf SβF. (3) where C A C p + C p + Cz + Cx C B Cn + Cz G G + G + G + G A Rp Rp Rz Rx G B GRn + GRz G Rp G Rp R p Rp G Rn G Rz G Rz R R R n z z G Rx. Rx Again the proposed circuit in Fig. 3b can be reanalyed the characteristic equation with (6). scc + scg ( + CG + C β g C g + G G + G g G g + g g A B A B B A B F mf BβS ms) A B BβF mf BβS ms βsβf ms mf. The CO FO become CAGB CBGA + CBβF CBβS (6) + (7) ωosc GG A B + GBβF GBβS+ βsβf (8) C C A where C A Cn + Cz + Cx + Cz C B Cx + C p G A GRn + GRz + GRx + GRz G B GRx + GRp. From (3) (8) it can be seen that the tracking error parasitic elements are degrade the performances of QO circuits. 5. COMPUTER SIMULATION To verify the theoretical analysis the QO circuit in Fig. 3 ( is chosen for example. The PSPICE simulation is used for performance tested with.5 μm CMOS technology [9]. The internal construction of VDTA is shows in Fig. [6] where it is used for this simulation. The aspect transistor ratios of p-types metal-oxide semiconductor (PMOS) n-types metal-oxide semiconductor (NMOS) are W/L. μm/.5 μm W/L μm/.5 μm respectively. The capacitors for this simulation are chosen as: C C 5 pf. In the proposed circuit the active elements are biased with ±.5 V the dc bias currents of VDTAs are chosen as I I μa I B BF BF BS 95 μa I BS 5 μa. The first results are the simulated for steady state response of quadrature outputs as shown in Fig. 5 from that the oscillation generates the

4 4 Mixed-mode quadrature oscillator 7 frequency of 5.8 MHz. It can be seen that the output waveforms are about 9º phase difference for both the voltage-mode current-mode. In addition the frequency spectrums of the output signals are displayed in Fig. 6. The percentage of the total harmonics distortion in Fig. 7 where I BS are varied as I BS 5μA μa 4 μa respectively. It is evident that the amplitude of output current I O will be higher when I BS is increased. In addition the AM signal can be generated at I O where I BS is sinusoidal signal when a frequency of 5 khz is applied. The AM signal is depicted in Fig. 8a. Similarly the ASK signal can be generated at I O when apply the square wave into I BS as illustrated in Fig. 8b. Fig. 7 Output current I O for difference I BS. Fig. 5 The steady state responses of output waveforms: voltage-mode; current-mode. Fig. 8 The AM signal at I O ; the ASK signal at I O. Fig. 6 The frequency spectrums of quadarture outputs: voltage-mode; current-mode. (% THD) for the voltage outputs are V O.7 % V O.77 % the currents are I O 4.46 % I O.53 %. To confirm the amplitude of I O can be electronically tuned with BS I as explained in (7). The I is shown output current I O for tuning dc bias current BS Fig. 9 The FO versus I BF.

5 7 Adirek Jantakun 5 To demonstrate of FO which can be electronically tuned by changing the bias current I BF with various capacitors. The results are exhibited in Fig. 9. It shows that the FO is proportional to the dc bias current I BF. Practically all capacitors have a specified tolerance such that affects the performance of the QO circuits. In this case Monte Carlo analysis can be conveniently used. The statistical results of Monte-Carlo analysis with 5 % tolerance of capacitors is shown in Fig.. The simulation uses times rom with Gaussian distribution. The histogram plots the maximum minimum of the FO are 6.33 MHz 5.45 MHz respectively. The stard deviation of FO is 9.73 khz. Fig. The statistical results of a Monte-Carlo analysis with 5 % tolerance of capacitors. 6. CONCLUSIONS The two QO circuits have been presented. The proposed circuits comprise two VDTAs two grounded capacitors. The CO FO can be adjusted electronically tuning by dc bias currents. The output signals are consisted voltage current-mode which are easy convenient for communication circuit/system. Furthermore the output current signal can be electronically controlled it would be easy to use is AM/ASK communication system. In addition the output currents have high impedance the circuit contains cascaded elements without additional current buffers. The performances of the proposed circuits have been evaluated through PSPICE simulation results. Received on July 4 REFERENCES. A. Iamarejin S. Maneewan P. Suwanjan W. Jaikla Current-mode variable current gain first-order allpass filter employing CFTAs Przegląd Elektrotechniczny 89 a pp W. Tangsrirat S. Unhavanich Signal flow graph realization of singleinput five-output current-mode universal biquad using current follower transconductance amplifiers Rev. Roum. Sci. Techn. Électrotechn. et Énerg. 59 pp J. Jerabek R. Soter K. Vrba Electronically adjustabla triple-input single-output filter with voltage differencing trans-conductance amplifier Rev. Roum. Sci. Techn. Électrotechn. et Énerg. 59 pp J. Jin P. Liang Resistorless current-mode quadrature oscillator with grounded capacitor Rev. Roum. Sci. Techn. Électrotechn. et Énerg pp M. Siripruchayanun W. Jaikla Cascadable current-mode biquad filter quadrature oscillator using DO-CCCIIs OTA Circuits Syst Signal Process 8 pp A. Jantakun W. Sa-ngiamvibool Current-mode sinusoidal oscillator using current controlled current conveyor transconductance amplifier Rev. Roum. Sci. Techn. Électrotechn. et Énerg pp N. Herensar R. Sotner J. Koton J. Misurec K. Vrba New compact VM four-phase oscillator employing only single Z-copy VDTA all grounded passive elements Elektronika ir Elektrotechnika 9 pp T. Pourak P. Suwanjan W. Jaikla S. Maneewan Simple quadrature sinusoidal oscillator with orthogonal control using single active element IEEE Int. Con. Electron. Devices Solid State Circuits (EDSSC) Thail pp K. Phanruttanachai W. Jaikla Third order current-mode quadrature oscillator with high output impedances World Academy of Science Engineering Technology 75 pp D. Prasad D. R. Bhaskar Electronically-controllable explicite current output sinusoidal oscillator employing single VDTA ISRN Electronics doi:.54// D. Prasad M. Srivastava D. R. Bhaskar Electronically controllable fully-uncoupled explicite current-mode quadrature oscillator using VDTAs grouded capacitors Circuits Systems 4 pp P. Phatsornsiri P. Lamun M. Kumngern U. Torteanchai Currentmode third-order quadrature oscillator using VDTAs grounded capacitors The Joint International Conference on Information Communication Technology Electronic Electrical Engineering (JICTEE 4) Thail O. Channumsin A. Jantakun Third-order quadrature oscillator using VDTAs grounded capacitors with amplitude controllability The Joint International Conference on Information Communication Technology Electronic Electrical Engineering (JICTEE 4) Thail D. Biolek R. Senani V. Biolkova Z. Kolka Active elements for analog signal processing: classifica-tion review new proposals Radioengineering 7 4 pp J. Satansup T. Pukkalanun W. Tangsrirat Electronically tunable single-input five-output voltage-mode universal filter using VDTAs grounded passive elements Circuits Syst Signal Process 3 pp A. Yesil F. Kacar H. Kuntman New simple CMOS realization of voltage differencing transconductance amplifier its RF filter application Radioengineering 3 pp A. F. Aebel L. Goldminz Output stage for current-mode feedback amplifiers theory applications Analog Integrated Circuits Signal Procesing pp