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Versatile Precision Full-Wave Rectifier Using Current and Voltage Conveyor Jaroslav Koton†1, Norbert Herencsár†2, Kamil Vrba†3 and Oguzhan Cicekoglu‡ †
Brno University of Technology, Dept. of Telecommunications, Purkynova 118, 612 00 Brno, Czech Republic
[email protected],
[email protected],
[email protected] ‡ Bogazici University, Dept. of Electrical and Electronic Engineering, 34342-Bebek-Istanbul, Turkey
[email protected]
Abstract – This paper describes a precision fullwave rectifier of minimal configuration that is able to process both low voltage and low current signals. The behavior of the proposed rectifier is compared with the opamp based circuit by evaluating their DC value transfers and RMS errors. Furthermore, experimental measurements were performed that shown the feasibility of the new circuit to process signal up to 100 kHz and beyond with no or small distortion. I. INTRODUCTION It is know that, because of the threshold voltage of the diodes, simple passive rectifiers operate inaccurately with small signal. Hence, precision rectifiers containing active elements have to be used. In instrumentation and measurement precise rectification is important in applications such as ac volt- and ampere-meters, signal-polarity detectors, peak value measurement, or averaging circuits [1]. Conventional rectifiers based on voltage feedback operational amplifiers suffer from the finite slew rate and effects caused by diode commutation. Therefore, these circuits operate well only at low frequencies but cause significant waveform distortions above about 1 kHz [2], [3]. A significant improvement has been achieved by using current-mode active elements, when diodes are connected to the high-impedance current outputs of these active elements. In [4]-[6] a full-wave rectifier using two second-generation current conveyors (CCII) and four diodes is presented that can be used in frequency range up to 100 kHz. Using the voltage or current biasing schemes [4], [6] the frequency range can be further extended. Another solution of the precision full-wave rectifier can be found in [7]. It is based on the circuit shown in Fig. 2c [1], only the voltage feedback amplifier OPA1 is replaced by operational conveyor [7] and later by current conveyor [3]. Here, we present new versatile full-wave rectifier that employs single current and voltage conveyor, and two diodes. The proposed circuit can be used to process both current and voltage signals. For voltage mode operation two additional resistors are to be used. Evaluating DC value transfers and RMS errors, the performance of the full-wave rectifier is compared with the conventional opamp based circuit. Experimental measurements are also presented.
II. CURRENT AND VOLTAGE CONVEYOR Current conveyors were presented in 1968 for the first time [8] (first generation current conveyor). Since then current conveyors received considerable attention and other generations (second and third) [9], [10] and types were proposed. These elements are now used with advantage in applications where the wide bandwidth or output current response is necessary. Even if different generations are described nowadays, the most often used one is the secondgeneration current conveyor CCII or other derived types, e.g. CCCII [11], DVCC [12], or ECCII [13] can be mentioned as examples. The behavior of the CCII in Fig. 1a can be described by following equations:
vX = vY , iY = 0 , iZ = iX .
(1)
The recent research also focuses on voltage conveyors (VCs) that have been defined as dual active elements to the current conveyors [14]. As in the theory of current conveyors, also here first-, secondand third-generation VC can be described [15]. The best known VC is the differential current voltage conveyor (DCVC+) [16] that is more often called the current differencing buffered amplifier (CDBA) [17]. In [18]-[20], the universal voltage conveyor (UVC) is presented that is advantageously used for the design of minimal configuration full-wave rectifier. The UVC is a 6-port active element (Fig. 1b), which has one voltage input X, two current differencing inputs YP and YN, and two mutually inverse voltage outputs ZP and ZN. The auxiliary voltage input W is used to determine the generation of the voltage conveyor [20]. The UVC is described by following set of equations:
iX = iYP − iYN , vYP = vYN = vW , vZP = vX , vZN = −vX .
(2a,b) (2c,d)
Fig. 1 Circuit symbol of a) CCII, b) UVC
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ISBN: 978-960-474-208-0
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III. PROPOSED FULL-WAVE RECTIFIER
IV. DC AND RMS ERROR ANALYSIS
The proposed current- and voltage-mode fullwave rectifiers are shown in Fig. 2a and Fig. 2b. To enable signal processing at higher frequencies than it is currently allowed by standard opamp based solution (Fig. 2c), the diodes are directly connected to the high impedance terminal Z of the current conveyor CCII as in [4]-[6]. Subsequently, the differential current inputs of the universal voltage conveyor are used with advantage and therefore only two diodes need to be used. Routine analysis of the current- and voltage-mode full-wave rectifier leads to following expressions:
To evaluate the accuracy of the proposed fullwave rectifier the DC value transfer pDC and RMS error pRMS have been analyzed [21]:
pDC =
∫y
R
(t )dt
ID
(t )dt
T
∫y
,
(4a)
T
pRMS =
∫[ y
(t ) − iID (t )] dt 2
R
T
∫y
2 ID
,
(4b)
(t )dt
T
iOUT (t ) = − iIN (t ) , vZP (t ) = −
(3a)
R2 R vIN (t ) , vZN (t ) = 2 vIN (t ) . (3b,c) R1 R1
The resistors R1 and R2 generally represent simple voltage-to-current and current-to-voltage convertors. Choosing proper values, the voltage gain of the rectifier can be easily adjusted. The further advantage of the rectifier is that working in the current-mode the input impedance is generally zero at ground potential and the output impedance is infinitely high in theory. Similarly, if the rectifier works in the voltage-mode the input impedance is infinitely high and the output impedance is zero.
where the yR(t) and yID(t) represent the actual and ideally rectified signal and T is the period of the rectified signal. The ideal behavior of the rectifier is characterized by the values pDC = 1 and pRMS = 0. Using (4) the proposed voltage-mode rectifier has been simulated using the models of CCII and UVC [22] and the behavior has been compared with the standard opamp based full-wave rectifier (Fig. 2c). The current and voltage transfer bandwidth of the CCII and UVC is about 35 MHz [22], hence for the simulations the opamp AD825 [23] has been used. The diodes are general-purpose 1N4148. The simulation results of the frequency dependent DC value transfer and RMS error for different values of amplitudes are shown in Fig. 3, where the solid and dashed lines stand for the conveyor and opamp based rectifier, respectively. If the frequency increases and/or amplitude decreases distortions occur and the pDC decreased below one and pRMS increases. 1
0.8
pDC [-]
0.6
0.4
0.2
VIN = 10 mV VIN = 100 mV VIN = 300 mV
0 4 10
5
10 Frequency [Hz]
10
6
a) 1 VIN = 10 mV
pRMS [-]
0.8
VIN = 100 mV VIN = 300 mV
0.6
0.4
0.2
Fig. 2 Proposed minimal configuration conveyor based full-wave rectifier working in the a) current-, b) voltage-mode, c) standard voltage feedback amplifier based full-wave rectifier [1]
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0 4 10
5
10 Frequency [Hz]
10
6
b) Fig. 3 a) DC value transfer, b) RMS error of the proposed rectifier in Fig. 2b (solid), and standard rectifier in Fig. 2c (dashed)
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V. EXPERIMENTAL MEASUREMENTS
feedback amplifier based rectifier. Here, it can be observed that the behavior of the designed conveyor based rectifier is very satisfactory. As shown in Fig. 4a,e,i at a 10 kHz input frequency significant distortions of the standard rectifier occur. At higher frequencies the full-wave rectification is already absent of the circuit in Fig. 2c. The proposed conveyor based circuit in Fig. 2b can be used to process signals at frequencies 100 kHz without causing any major distortions and even at higher frequencies the full-wave rectification can be still observed.
The behavior of the proposed voltage-mode fullwave rectifier has also been verified by experimental measurements. As active elements the universal current UCC-N1B and universal voltage conveyors UVC-N1C have been used, both produced as laboratory samples by AMI Semiconductor LtD. (now ON Semiconductor LtD.) [20], [22]. The transient measurement results of the proposed voltage-mode rectifier for different frequencies and amplitudes of the input voltage are shown in Fig. 4 and compared with the measurements of the voltage
a)
e)
i)
b)
f)
j)
c)
g)
k)
d) h) l) Fig. 4 Transient responses of the minimal configuration full-wave rectifier in Fig. 2b (black line) and of the standard rectifier in Fig. 2c (gray line) for signal frequencies and amplitudes: a) f = 10 kHz, Vin = 100 mVpp, b) f = 50 kHz, Vin = 100 mVpp, c) f = 100 kHz, Vin = 100 mVpp, d) f = 500 kHz, Vin = 100 mVpp, e) f = 10 kHz, Vin = 300 mVpp, f) f = 50 kHz, Vin = 300 mVpp, g) f = 100 kHz, Vin = 300 mVpp, h) f = 500 kHz, Vin = 300 mVpp, i) f = 10 kHz, Vin = 500 mVpp, j) f = 50 kHz, Vin = 500 mVpp, k) f = 100 kHz, Vin = 500 mVpp, l) f = 500 kHz, Vin = 500 mVpp.
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ISBN: 978-960-474-208-0
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VI. CONCLUSION In this paper new minimal configuration full-wave rectifier using current and voltage conveyors has been presented. Since the diodes are directly connected to the high-impedance current-output terminal the rectifier can be used to process signals at frequencies at 100 kHz without causing significant distortions. Even at higher frequencies the full-wave rectification is still preserved. Further advantage is in the use of only two diodes and the possibility of working in the voltage-, currentand mixed-mode. Experimental measurements were also performed that proved the feasibility of the circuit. ACKNOWLEDGEMENT The research of non-linear circuits is supported by the Czech Science Foundation project no. P102/10/P561, by BUT project no. FEKT-S-10-16, and by research project no. MSM0021630513 REFERENCES [1] U. Tietze, Ch. Schenk, and E. Gramm: “Electronic Circuits-Handbook for Design and Application,” Springer, 2008. [2] C. Toumazou and F. J. Lidgey, “Fast currentmode precision rectifier,” Electron. Wireless Wolrd, vol. 93, no. 1621, pp. 1115-1118, 1987. [3] S. J. G. Gift and B. Maundy, “Versatile Precision Full-Wave Rectifiers for Intrumentation and Measurements,” IEEE Trans Instrum. Meas., vol. 56, no. 5, pp. 1703-1710, 2007. [4] C. Toumazou, F. J. Lidgey, and S. Chattong, “High frequency current conveyor precision fullwave rectifier,” Electronics Letters, vol. 30, no. 10, pp. 745-746, 1994. [5] A. A. Khan, M. A. El-Ela, and M. A. Al-Turaigi, “Current-mode precision rectification,” Int. J. Electron., vol. 79, no. 6, pp. 853-859, 1995. [6] B. Wilson and V. Mannama, “Current-mode rectifier with improved precision,” Electronics Letters, vol. 31, no. 4, pp. 247-248, 1995. [7] S. J. G. Gift, “A High-performance full-wave rectifier circuit,” Int. J. Electron., vol. 87, no. 8, pp. 925-930, 2000. [8] K. C. Smith and A. Sedra, “The current conveyor: a new circuit building block,” IEEE Proc., vol. 56, pp. 1368-1369, 1968. [9] A. Sedra and K. C. Smith, “A second-generation current conveyor and its application,” IEEE Trans. Circuit Theory, vol. 17, pp. 132-134, 1970.
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[10] A. Fabre, “Third-generation current conveyor: a new helpful active element,” Electronics Letters, vol. 31, no. 5, pp. 338-339, 1995. [11] A. Fanre, O. Saaid, F. Wiest, and C. Boucheron, “High frequency applications based on a new current controlled conveyor,” IEEE Trans. Circuits Syst.-I, vol. 43, no. 2, pp. 82-90, 1996. [12] H. O. Elwan and A. M. Soliman, “Novel CMOS differential voltage current conveyor and its applications,” IEE Proc. Circuits, Devices, Systems, vol. 144, no. 3, pp. 195-200, 1997. [13] W. Surakampontorn and K. Kumwachara, “CMOS-based electronically tunable current conveyor,” Electronics Letters, vol. 28, no. 14, pp. 1316-1317, 1992. [14] I. M. Filanovsky and K. A. Stromsmoe, “Current-voltage conveyor,” Electronics Letters, vol. 17, no. 3, pp. 129-130, 1981. [15] T. Dostal and J. Pospisil, “Hybrid models of 3port immittance convertors and current and voltage conveyors,” Electronics Letters, vol. 18, no. 20, pp. 887-888, 1982. [16] K. Salama and A. Soliman, “Novel MOS-C quadrature oscillator using the differential current voltage conveyor,” in Proc. 42nd Midwest Symposium on Circuits and Systems – MWSCAS 99, Las Cruces, USA, pp. 279-282, 1999. [17] C. Acar and S. Ozoguz, “A new versatile building block: current differencing buffered amplifier suitable for analog signal processing filters,” Microelectronics Journal, vol. 30, no. 2, pp. 157-160, 1999. [18] J. Koton, K. Vrba, and N. Herencsár, “Tuneable filter using voltage conveyors and current active elements,” Int. J. Electron., vol. 96, no. 8, pp. 787-794, 2009. [19] N. Herencsár, J. Koton, and K. Vrba, “A new electronically tunable voltage-mode active-C phase shifter using UVC and OTA,” IEICE Electronics Express, vol. 6, no. 17, pp. 12121218, 2009. [20] J. Koton, N. Herencsár, and K. Vrba, “KHNequivalent voltage-mode filters using universal voltage conveyors,” AEU – Int. J. Electronics Communications, available online, doi:10.1016/j.aeue.2010.02.005, 2010. [21] D. Biolek, V. Biolkova, and Z. Kolka, “AC Analysis of Operational Rectifiers via Conventional Circuit Simulators,“ WSEAS Transactions on Circuits and Systems, vol. 3, no. 10, pp. 2291– 2295, 2004. [22] R. Sponar and K. Vrba, “Measurements and Behavioral Modeling of Modern Conveyors,” Int. J. Comp. Science Net. Secur. IJCSNS, vol. 6, mo. 3A, pp. 57-65, 2006. [23] Datasheet AD825, Rev. F, 11/2004.
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