International Journal of Electrical and Computer Engineering (IJECE) Vol.
No.
August 2017, pp.
ISSN: 2088-8708.
DOI: 10.
11591/ijece.
New Realization of Quadrature Oscillator using OTRA Gurumurthy Komanaplli.
Neeta Pandey.
Rajeshwari Pandey Departement of Electronics and communication Engineering.
Delhi Technological University.
India
Article Info
ABSTRACT
Article history:
In this paper a new, operational transresistance amplifier (OTRA) based, third order quadrature oscillator (QO) is presented.
The proposed structure forms a closed loop using a high pass filter and differentiator.
All the resistors employed in the circuit can be implemented using matched transistors operating in linear region thereby making the proposed structure fully integrated and electronically tunable.
The effect of non-idealities of OTRA has been analyzed which suggests that for high frequency applications self-compensation can be used.
Workability of the proposed QO is verified through SPICE simulations using 0.
18m AGILENT CMOS process parameters.
Total harmonic distortion (THD) for the proposed QO is found to be less than 2.
The sensitivity, phasenoise analysis is also discussed for the proposed structure.
Received Oct 14, 2016 Revised May 27, 2017 Accepted Jun 14 2017 Keyword:
OTRA
Phasenoise Quadrature oscillator Sensitivity THD Copyright A 2017 Institute of Advanced Engineering and Science.
All rights reserved.
Corresponding Author:
Gurumurthy Komanaplli .
Department of Electronics and communication Engineering.
Delhi Technological University.
Bawana Road.
New Delhi.
India-110085.
Email: murthykgm@gmail.
INTRODUCTION
In last few decades current-mode (CM) processing has evolved as a promising design technique to provide efficient solutions to circuit design problems.
This evolution has resulted in emergence of numerous CM analog building blocks .
The operational trans resistance amplifier (OTRA) is one among these blocks.
It is a high gain current input, voltage output amplifier .
and uses current feedback technique which makes its bandwidth almost independent of the closed loop gain.
Additionally it is free from the effect of parasitic capacitances at the input due to virtually internally grounded input terminals .
and hence non-ideality problem is less in circuits implemented using OTRA.
Quadrature oscillators (QO) are an important class of circuits and find wide application in communication, power electronics and instrumentation.
This has led a consistent research effort towards second order QO design using wide variety of active blocks, as is evident from vast literature available .
It is well known that higher order networks, provide better accuracy, frequency response and distortion performance .
as compared to lower order circuits.
Owing to this in recent past few third order QO designs .
, .
, .
have been reported.
Realizing sinusoidal oscillator using closed loop with positive feedback is a well-established method.
A careful observation suggests that all the reported third order QO designs are based on forming closed loop using combinations of lossy and/or lossless integrators.
In this paper a new OTRA based third order QO is proposed that adapts the scheme of using second order high pass filter and a differentiator in a feedback loop .
A comparative statement of the proposed structure with previously reported QO circuits is recorded in Table 1.
It may be observed from the table that the available topologies-presented in .
are realized using op-amps however, the constant gain-bandwidth product and lower slew rate of the op-amps limit their high frequency operations.
Additionally these circuits use more number of active components as compared to proposed circuit Lack electronic tunability .
, .
, .
, .
Use mix of active blocks such as DDCC and OTA .
,cDTA and OTA .
,cTA and OTA .
Journal homepage: http://iaesjournal.
com/online/index.
php/IJECE A ISSN: 2088-8708 Provide voltage output at high impedance .
, .
, .
, .
, .
, .
, .
, .
, .
making a buffer necessary to drive the voltage input circuits Provide current output .
, .
which need to be converted to voltage for circuits requiring voltage inputs and would considerably increase the component count Table 1.
A comparative statement of the proposed structure with previously reported QO circuits Ref.
Active No of active CCII
OTA
CDTA
Op-amp
CCII
DVCC
CDTA
OTRA
DDCC
and OTA
cDTA
and OTA
and OTA
DVCCTA
OTRA
Proposed OTRA
Close loop
Passive elements formation scheme
C R
Fig.
1, two lossy and one lossless integrators Fig.
2, -do5 3 Fig.
Intuition Fig.
7, two lossy and one lossless integrators Fig.
9, -do3 1
-do3 0
-do3 5
-do5 3
A second order low pass
filter and an integrator -do3 0
one lossy and two
lossless integrators Cascade of three LPFs
with gained feedback
A second order LPF and an integrator -do3 0
-do3 4
-do3 0
Electronic Output Output
Floating Type
Impedance passive Compnents Voltage High
Voltage Voltage Voltage High
High
High
Voltage Current
Voltage Voltage High
High
Low
Low
Both Current
High
High
Both High
Voltage High
Voltage Both Voltage Current
High
High
Low
High
R1 C
-do- Voltage High -do- Both High Current Both Both Voltage Voltage Voltage High High High Low Low Low -doFig.
HPF and differentiator Fig.
6, -doFig.
2,LPF and integrator Fig.
3,HPF and differentiator Fig.
2HPF and differentiator R2,R3,C1,C2 R1,R2,C2,C3 R1 C Above discussion suggests that OTRA based QO is most suitable choice for voltage output Rest of the paper is as organized as follows: in section 2 proposed circuit is described followed by Effect of nonideality of OTRA is dealt in section 3.
Section 4 explains the MOS-C implementation details of proposed structure.
Proposed structured is verified experietally by contructing OTRA using offshelf ICAos AD844 .
, phase noise analysis using the method discussed in .
, .
is presented in section 5.
Sensitivity analysis are discussed in section 6.
The simulation and experimental results are presented in section 7 and paper is concluded in section 8.
PROPOSED CIRCUIT
The circuit symbol of OTRA is shown in Figure 1 and its port characteristics are given by EV p E E0
E E E
EVn E A E0
EV E E R
E 0E E m
A Rm
0E E I p E
E E
0EE E I n E
0 E EE I 0 EE
The output voltage is the difference of two input currents multiplied by trans-resistance gain (R.
Ideally the trans-resistance gain Rm approaches infinity and therefore the OTRA must be used in a negative feedback configuration .
The proposed QO topology is shown in Figure 2.
It uses an OTRA based second order high pass filter .
(C1=C.
and an inverting differentiator in the feedback forming a closed loop, which results in a third order characteristic Equation given by IJECE Vol.
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C E
s 3C1C3 RDCD A s 2C1C2 A sEE 1 A 2 EE A A0
R1 E R1R2
E R2
Figure 1.
OTRA circuit Figure 2.
Proposed circuit
Assuming C2=C1 the condition of oscillation (CO) and frequency of oscillation (FO) O: f A R1 A R2
2A C 3 R1 R2 R D C D
CO: ( R1 A R2 )C2 A RD CD
The FO can be adjusted to desired value through R1.
R2 and proper selection of resistor RD would satisfy the CO.
NONIDEAL ANALYSIS
Ideally the transresistance gain Rm is assumed to approach infinity.
However, practically R m is a frequency dependent finite value.
The output of the QO may deviate due to non-ideality of OTRA in practice.
Considering a single pole model for the trans-resistance gain.
Rm can be expressed as E
Ro E
Rm ( s ) A E
E1A
Ao E Where Ro represents the dc transresistance gain.
For high frequency applications the transresistance gain Rm .
reduces to Rm ( s ) A sC P where C P A RO AO Taking this effect into account the characteristic Equation given by .
modifies to Ws3 A Xs 2 A Ys A Z A 0 Where the coefficients W.
Y, and Z can be expressed as W A CC2CP RD A CP2CRD A C 2CD RD New Realization of Quadrature Oscillator using OTRA (Gurumurthy Komanapll.
A ISSN: 2088-8708
X A CC2 A CC P A CC P
A C P C 2 D A C P2 C D
Y A C A (C 2 A C P ) A RD C P .
Z A
R1 R2
R1R2
Due to parasitic effect the FO and CO also change and are given by .
respectively FO: f A CO:
RD C P
C C2 A C P
R1 A R2 R2
C 2 C D RD A CRD (C 2 A C P )
(C2 A C P ) R2 A CR1 A C P RD A
R1 R2 RD {C (C2 A C P ) A C 2C D }
R2 (C A C P ) AR1 C A RD C P A A R1 RD C P C
As the parasitic capacitance of the OTRA is very small, using approximation (C 2 A C P ) C C the W.
Y and Z coefficients can be simplified as W A CC2 C P RD A C P2 CRD A C 2 C D RD
A CRD AC P (C 2 A C P ) A CCD A
C CRD AC P C A CCD A C C 2 RD AC P A C D A C C 2 RD C D
X A CC2 A CC P A CC P
A C P C 2 D A C P2 C D
A C (C 2 A C P ) A C P (C 2 A C P )
A DC C
R2 P
R E
C C 2 A CC P EE D A D EE
R2 E
E 1
C C 2 as CCP AA C 2
(C A C P ) R D C P
R C
A 2
CY A
A D P
R1 R2
R1 R2
and Z A R1R2 as C P AA C By substituting W.
Z from .
, .
, .
the characteristic Equation and hence the FO and CO can be obtained which are same as given by .
, .
MOS-C IMPLEMENTATION
The differential input of OTRA allows the resistors connected to the input terminals of OTRA to be implemented using MOS transistors with complete non-linearity cancellation .
Each resistor implementation require two matched N MOS transistorsas shown in Figure 3.
Figure 4 shows a typical MOS based implementation of resistance connected at inverting terminal of OTRA where nodes X and Y need to be connected to inverting and non-inverting terminals of the OTRA The value of resistance so obtained is expressed as RA A n C ox (W / L)(Va A Vb ) .
Where .
COX and W/L represent standard transistor parameters and V a and Vb are the gate voltages.
The MOS based implementation of the proposed circuit of Figure 2 is shown in Figure 4.
The resistance value may be adjusted by appropriate choice of gate voltages thereby making oscillator parameters electronically tunable.
IJECE Vol.
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Figure 3.
The MOS based resistor .
A Figure 4.
The MOS based implementation of QO Circuit
PHASE NOISE ANALYSIS
The random frequency fluctuations in a phase of a signal can be treated as a phase noise.
calculates the phase noise a procedure discussed in .
, .
is adopted.
The open loop transfer function H.
of the oscillator circuit of Figure 2 is given by H ( .
A A s 3C1C3C D R D R1 R2 .
A sCR1 ).
A sCR2 ) .
The H.
given by .
can also be expressed in terms of magnitude and phase as H ( jA) A A(A).
e jAA From .
dA E e jAA
E dA
A E
dA E E dA Substituting the CO and FO of the proposed oscillator in .
the magnitude A(O) can be written as E A E
EE A
E Ao E
A(A ) A
1 E A E
E AA2
E A
E C R EA E
C ( R1 A R2 ) E
D D E o E Determining from .
results in dA
E AC D RD
EA E
CA EE EE ( R1 A R2 ) E
EaH (A ) A A A ATanA1 E
E oE
EA E
EE EE
E Ao E Determining dA results in dA dA A o2 C D RD From Equation .
it is clear that Frequency stability of proposed quadrature oscillator decreases with increase of Ao .
New Realization of Quadrature Oscillator using OTRA (Gurumurthy Komanapll.
A ISSN: 2088-8708
SENSITIVITY ANALYSIS
The sensitivity is an important performance criterion of any network.
The sensitivity of FO ( Ao ) with respect to a circuit parameters, say Y is given as SYAo A CAo Y CY Ao Using this definition, the sensitivity of FO ( Ao ) for the circuit w.
t R1.
R2.
C are given as SCAo A SCAo A S RAo A S RAo = 2( R1 A R2 ) 2( R1 A R2 ) From the above Equations it is observed that all passive sensitivities for both the circuits are lower than unity in magnitude.
It ensures that the sensitivity performance is good.
SIMULATION AND EXPERIMENTAL RESULT
The proposed QO is verified through simulations using the CMOS implementation of the OTRA .
The SPICE simulations are performed using 0.
18AAm CMOS process parameters provided by MOSIS (AGILENT).
Supply voltages taken are A1.
Component values are chosen as C1=C2=C3=CD=100pF and R1=R2=5K.
RD=10KThe simulated FO was observed to be 320 KHz as against the calculated value of 47 KHz.
The simulated transient output and corresponding frequency spectrum are shown in Figure 5.
Figure 5.
Transient Output .
Frequency spectrum of proposed QO circuit.
Figure.
Frequency Tuning with .
Resistance .
with Capacitance for circuit IJECE Vol.
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The FO of the proposed QO can be tuned through R or C variations, as suggested by .
The FO tuning with R .
aried from 3k to 6.
while keeping C fixed .
pF) is shown in Figure 6.
whereas tuning with C .
aried from 60pF to 140pF) with R fixed at 5k is depicted in Figure 6.
It may be observed that the simulated and theoretical values of FO are in close agreement.
The %THD variation with R and C is also studied and is depicted in Figure 7.
The %THD variation with R (C = 100pF) for both Quadrature outputs, is recorded in Figure 7.
and the largest value observed is Similarly Figure 7.
shows %THD variation with C (R= 5.
where in the maximum observed value is well within 2.
The phase error plots between V out1 and Vout2 are drawn in Figure 8.
Variation of phase error with resistance and capacitance are depicted in Fig.
Figure 7.
The % THD variation with .
Resistance .
Capacitance for circuit .
Figure 8.
Phase error between Vout1 and Vout2 with .
Capacitance .
Resistance for circuit Figure.
Plot of Vout1 vs Vout2 Figure.
Transient Response of Proposed circuit on CRO New Realization of Quadrature Oscillator using OTRA (Gurumurthy Komanapll.
A ISSN: 2088-8708 The plot of Vout1 vs Vout2 is shown in Figure 9.
The proposed quadrature oscillator is also tested experimentally by bread boarding the circuit of Figure 2 and the corresponding transient response shown in Figure 10.
The OTRA is realized using Current feedback operational amplifier (CFOA) IC AD844AN .
with power supply of A 8V.
CONCLUSION
New realization of OTRA based third order quadrature oscillator is presented in this paper using a high pass filter and a differentiator.
The functionality of proposed structure is verified through SPICE simulations using 0.
18 AAm technology parameter.
This topology is further tested experimentally where in the OTRA is realized using off the shelf CFOA IC AD844.
The simulation and experimental results are found to be in close agreement with theoretical propositions.
The simulated value of % THD is quite low.
The phase noise analysis is also discussed for the proposed Q.
The sensitivity of O w.
t passive components is also calculated and observed to be low.
REFERENCES