![ACEEE Int. J. on Signal & Image Processing, Vol. 03, No. 01, Jan 2012
Implementation of Fully Differential OTA based on
Commercially Available IC for Biquadratic Filter
Application
C. Chanapromma1 and P. Silapan2
1, 2
Faculty of Industrial Technology, Uttaradit Rajabhat University, Muang, Uttaradit, 53000, THAILAND
Email: chaiyanc@uru.ac.th1 and phamorn@mail.uru.ac.th 2
Abstract—This article presents a realization of a recently basic agreement as theoretically depicted.
building block for analog signal processing, namely fully
differential operation transconductance amplifier (FD-OTA) II. FD-OTA CONFIGULATION
using the commercially available ICs (LT1228). The proposed
element has very simple internal instruction. The An ideal FD-OTA has infinite input and output
performances are examined through PSpice simulations. The impedances. The output current of a device is given by
description include example as biquadratic filter topology.
They show good agreement as theoretically depicted.
I o g m (Vi Vi ) (1)
and
Index Terms—FD-OTA, commercially available IC, biquadratic
I o g m (Vi Vi ) (2)
filter, building block application
where gm is transconductances gain of the FD-OTA. For
I. INTRODUCTION LT1228 commercially available IC of the OTA can be express
by
The operational transconductance amplifier (OTA) is a
basic building block in analog circuit applications [1], such IB
gm . (3)
as wireless communication, computer systems, biomedical 3.87VT
circuits, and instrumentation and control systems [2-3]. The Where VT is the thermal voltage (about 25mV at room
OTA received considerable attention as active components, temperature). The symbol and equivalent circuit of the FD-
because the transconductance can be adjusted electronically. OTA are illustrated in Fig. 1(a) and (b), respectively. The
The key function of the OTA is to convert the input voltage proposed implementation of FD-OTA based on LT1228
into the output current while accuracy and linearity are both commercially available IC is shown in Fig.2. The output current
maintained [4]. The flexibility of the device to operate in both of the FD-OTA for non-ideal case is given by
current and voltage-modes allows for a variety of circuit
designs. The fully differential (FD) structures are often used I o o g m (Vi Vi ) o (4)
in industrial products because of the improved dynamic range and
over their single-ended counterpart [5]. This is due to the I o o gm (Vi Vi ) o
(5)
properties of the FD structures have better common-mode
noise rejection, reduce harmonic distortion, and increased where o and o are current gain error and current offset
output current swing [6]. Recently, FD-OTA has been often error, respectively.
used in many filter applications such as OTA-C filter in [7-
14]. The OTA-C filters are an attractive choice for applications
where a tunable filter is required. Even when the tunability in
frequency is not a requisite, these filters can easily be used
with an automatic frequency tuning system [15]. Structures
are well known for realizations of simple filters as biquads,
that can be cascaded for more complex filters, for simulations
of passive doubly-terminated LC filters [16], preferred for Figure 1. The FD-OTA (a) Symbol (b) Equivalent circuit
their low sensitivity to element variations, and for other kinds
of filters. However, FD-OTA is an important element building
block for filters, but it is not implementation in commercially
available IC. This paper proposes the implementation of FD-
OTA that is implementation by using commercially available
ICs (LT1228). The proposed element has very simple internal
instruction. The performances of the proposed FD-OTA are
proved by PSpice simulations. The application example as a Figure 2. Implementation of the FD-OTA based on commercially
biquadratic low pass filter is included. They show good available ICs
© 2012 ACEEE 59
DOI: 01.IJSIP.03.01. 18](https://image.slidesharecdn.com/18-120926225534-phpapp02/85/Implementation-of-Fully-Differential-OTA-based-on-Commercially-Available-IC-for-Biquadratic-Filter-Application-1-320.jpg)
![ACEEE Int. J. on Signal & Image Processing, Vol. 03, No. 01, Jan 2012
CONCLUSIONS [5] A. N. Mohieldin, E. S. Sinencio and J. S. Martinez, “Nonlinear
effects in pseudo differential OTAs with CMFB,” IEEE Transaction
The building block, called the FD-OTA implemented by on circuits and systems-II, vol. 50, pp. 762-770, 2003.
using commercially available ICs, has been introduced via [6] A. N. Mohieldin, E. S. Sinencio and J. S. Martinez, “A fully
this paper. The internal construction is very simple. The balanced pseudo-differential OTA with common-mode feedforward
usabilities have been verified by the simulation and and inherent common-mode feedback detector,” IEEE journal of
application example. The application circuit is biquadratic solid-state circuits, vol.38, pp.663-668, 2003.
low pass filter. They show good agreement as theoretically [7] M. A. Tan and R. Schaumann, “Simulating general-parameter
depicted. Our future work is to find more applications of the LC-ladder filters for monolithic realizations with only
transconductance elements and grounded capacitors,” IEEE
FD-OTA, emphasizing on the current-mode and voltage-mode
Transactions on circuits and systems, vol. 36, no. 2, pp. 299-307,
applications such as signal generator, rectifier, filter and etc. February, 1989.
[8] A. C. M. de Queiroz and L. P. Caloba, “Reactive loop
ACKNOWLEDGMENT elimination and the use of special approximations in the design of
OTA-C filters,” MWACAS 1955, vol. 2, pp. 1341-1344, 1995.
The authors wish to thank Mr. Amnaj Prajong, Faculty of
[9] F. A. P. Barúqui, A. Petraglia and E. Rapoport, “IC design of
Agricural and Industrial Technology, Nakhon Sawan an analog tunable crossover network,” ISCAS 2005, vol. 2, pp.
Rajabhat University. This work was supported in part by a 1012-1015, 2005.
grant from the Research and Development Institute, Uttaradit [10] C. L. Hsu, M. H. Ho, Y. K. Wu and T. H. Chen, “Design of
Rajabhat University (URU). low-frequency low-pass filters for biomedical applications,”
APCCAS 2006, pp. 690-695, 2006.
REFERENCES [11] J. Mahattanakul and P. Khumsat, “Structure of complex elliptic
Gm-C filters suitable for fully differential implementation,” IET
[1] T. K. Nguyen and S. G. Lee, “Low-voltage, low power CMOS Circuits Devices Systems, vol. 1, no. 4, pp. 275-282, August 2007.
operational transconductance amplifier with rail-to-rail differential [12] P. Mongkolwai, T. Pukkalanun and W. Tangsrirat, “Current-
input range,” ISCAS 2006, pp. 1639-1642, 2006. mode universal biquad with orthogonal ùo-Q tuning using OTAs,”
[2] S. Koziel, R. Schaumann and H. Xiao, “Analysis and ICICS 2007, pp.1-4, 2007.
optimization of noise in continuose-time OTA-C filters,” IEEE [13] X. Zhang and E. E. Masry, “A novel CMOS OTA based on
Transaction on circuits and systems-I: Regular papers, vol. 52: pp. body-driven MOSFETs and it’s applications in OTA-C filters,”
1086-1094, 2005. IEEE IEEE Transaction on circuits and systems-I, vol. 54, no. 6,
[3] C. Chanapromma and K. Daoden, “A CMOS fully differential pp.1204-1212, June 2007.
operational transconductance amplifier operating in Sub-threshold [14] T. Y. Lo and C. C. Hung, “A 1 GHz equiripple low-pass filter
region and its application,” ICSPS 2010, vol. 2, pp. 73–77, July with a high-speed automatic tuning scheme,” IEEE Transaction on
2010. very large scale integration (VLSI) systems, pp.1-7, 2009.
[4] T. Y. Lo and C. C. Hung, “A 1 GHz OTA-based lo-pass filter [15] A. C. M. de Queiroz, “Balanced transconductor-c ladder filters
with a high speed automation tuning scheme,” IEEE Asia solid- with improved linearity,” MWSSCAS 2009, pp. 41-45, 2009.
stage conference, pp. 408-411, 2007. J. Schechtman, A. C. M. de Queiroz, and L. P. Caloba, “A high
performance balanced MOS transconductor,” 36th MWSCAS, pp.
1378-1381, August 1993.
© 2012 ACEEE 62
DOI: 01.IJSIP.03.01.18](https://image.slidesharecdn.com/18-120926225534-phpapp02/85/Implementation-of-Fully-Differential-OTA-based-on-Commercially-Available-IC-for-Biquadratic-Filter-Application-4-320.jpg)
Implementation of Fully Differential OTA based on Commercially Available IC for Biquadratic Filter Application
- 1. ACEEE Int. J. on Signal & Image Processing, Vol. 03, No. 01, Jan 2012 Implementation of Fully Differential OTA based on Commercially Available IC for Biquadratic Filter Application C. Chanapromma1 and P. Silapan2 1, 2 Faculty of Industrial Technology, Uttaradit Rajabhat University, Muang, Uttaradit, 53000, THAILAND Email: chaiyanc@uru.ac.th1 and phamorn@mail.uru.ac.th 2 Abstract—This article presents a realization of a recently basic agreement as theoretically depicted. building block for analog signal processing, namely fully differential operation transconductance amplifier (FD-OTA) II. FD-OTA CONFIGULATION using the commercially available ICs (LT1228). The proposed element has very simple internal instruction. The An ideal FD-OTA has infinite input and output performances are examined through PSpice simulations. The impedances. The output current of a device is given by description include example as biquadratic filter topology. They show good agreement as theoretically depicted. I o g m (Vi Vi ) (1) and Index Terms—FD-OTA, commercially available IC, biquadratic I o g m (Vi Vi ) (2) filter, building block application where gm is transconductances gain of the FD-OTA. For I. INTRODUCTION LT1228 commercially available IC of the OTA can be express by The operational transconductance amplifier (OTA) is a basic building block in analog circuit applications [1], such IB gm . (3) as wireless communication, computer systems, biomedical 3.87VT circuits, and instrumentation and control systems [2-3]. The Where VT is the thermal voltage (about 25mV at room OTA received considerable attention as active components, temperature). The symbol and equivalent circuit of the FD- because the transconductance can be adjusted electronically. OTA are illustrated in Fig. 1(a) and (b), respectively. The The key function of the OTA is to convert the input voltage proposed implementation of FD-OTA based on LT1228 into the output current while accuracy and linearity are both commercially available IC is shown in Fig.2. The output current maintained [4]. The flexibility of the device to operate in both of the FD-OTA for non-ideal case is given by current and voltage-modes allows for a variety of circuit designs. The fully differential (FD) structures are often used I o o g m (Vi Vi ) o (4) in industrial products because of the improved dynamic range and over their single-ended counterpart [5]. This is due to the I o o gm (Vi Vi ) o (5) properties of the FD structures have better common-mode noise rejection, reduce harmonic distortion, and increased where o and o are current gain error and current offset output current swing [6]. Recently, FD-OTA has been often error, respectively. used in many filter applications such as OTA-C filter in [7- 14]. The OTA-C filters are an attractive choice for applications where a tunable filter is required. Even when the tunability in frequency is not a requisite, these filters can easily be used with an automatic frequency tuning system [15]. Structures are well known for realizations of simple filters as biquads, that can be cascaded for more complex filters, for simulations of passive doubly-terminated LC filters [16], preferred for Figure 1. The FD-OTA (a) Symbol (b) Equivalent circuit their low sensitivity to element variations, and for other kinds of filters. However, FD-OTA is an important element building block for filters, but it is not implementation in commercially available IC. This paper proposes the implementation of FD- OTA that is implementation by using commercially available ICs (LT1228). The proposed element has very simple internal instruction. The performances of the proposed FD-OTA are proved by PSpice simulations. The application example as a Figure 2. Implementation of the FD-OTA based on commercially biquadratic low pass filter is included. They show good available ICs © 2012 ACEEE 59 DOI: 01.IJSIP.03.01. 18
- 2. ACEEE Int. J. on Signal & Image Processing, Vol. 03, No. 01, Jan 2012 III. SIMULATION RESULTS To prove the performances of the proposed FD-OTA, the PSpice simulation program was used for the examination. We use the conventional OTA LT1228 models from the PSpice library. The supply voltage VCC = -VEE were set to 15V. A wide range of the transconductance controllability can be achieved as shown in Fig. 3, when I B is varied from 1µA 1mA . DC transfer characteristics between voltage differential input Vid Figure 6. Frequency response of output terminal relative to vi and current output I o are shown in Fig. 4. DC characteristics between voltage differential input Vid and transconductance gm, when I B is varied, 10µA/step of 10 steps, from 10µA to 1mA, are shown in Fig. 5. The bandwidths of the output terminals relative to vi and vi are shown in Fig. 6 and Fig.7, respectively. The 3dB respon ses of I o / Vi , I o / Vi , I o / Vi and I o / Vi is loca ted at 13.283MHz. The power consumption relative to IB is shown Figure 7. Frequency response of output terminal relative to vi in Fig. 8, when IB is varied from 10µA to 1mA. Conclusions of FD-OTA parameters are displays in Table I. Figure 3. Transconductance relative to I B. Figure 8. Power consumptions relative to I B TABLE I. CONCLUSIONS O F FD-OTA PARAMETERS Figure 4. DC transfer characteristics Figure 5. Transconductance relative to v id and I B © 2012 ACEEE 60 DOI: 01.IJSIP.03.01.18
- 3. ACEEE Int. J. on Signal & Image Processing, Vol. 03, No. 01, Jan 2012 From (11) can be re-expressed as p o 1 (13) 2 gm C1C2 The biquadratic filter topology in Fig. 9 was designed to have low pass filter response for C1=C2=14.14nF. The designed filter was simulated with PSpice program. Fig.10 Figure 9. Conventional biquadratic OTA-C filter topology shows simulated the AC frequency response of the designed IV. APPLICATION EXAMPLE AND SIMULATION RESULTS filter with differential bias current. Differential mode and common mode gain are shown in Fig.11. The frequency The application of the proposed FD-OTA based on response of the total noise for the filter topology is shown in commercially available IC is biquadratic filter shown in Fig. 9. Fig.12. Output and input transient waveforms are shown in It consists of 4 FD-OTAs. Considering the circuit in Fig. 9, Fig.13. and using the FD-OTA properties, yields the transfer function voltages as follows 2 4 gm v v C1C2 H s o o 2 . v v i 2i 2gm 4gm (6) s s C2 C1C2 The transfer function of the general low pass biquadratic filter can be express by Figure 10. Frequency response biquadratic filter at different bias cu rrent 2 p H s . Q s2 2 s p (7) p Comparing (6) and (7), the following expression can be derived 1 p 2gm (8) C1C2 and Figure 11. Frequency response of differential and common mode 2 4 gm 1 Q . (9) C2 C1C2 Considering the circuit in non-ideal case, yields the transfer function voltages as follows 2 2 4 o g m C1C2 H s . 2 2 o g m 4 o2 g m 2 (10) s s C2 C1C2 Figure 12. Frequency response of the total output noise for the biquadratic filter It is clearly seen from (10), FD property is that the offset error can be cancelation. Comparing (7) and (10), the following expression can be derived 1 p 2 o g m (11) C1C2 and 4 o2 gm 2 1 Q . (12) C2 C1C2 Figure 13. Transient waveforms of biquadratic filter © 2012 ACEEE 61 DOI: 01.IJSIP.03.01.18
- 4. ACEEE Int. J. on Signal & Image Processing, Vol. 03, No. 01, Jan 2012 CONCLUSIONS [5] A. N. Mohieldin, E. S. Sinencio and J. S. Martinez, “Nonlinear effects in pseudo differential OTAs with CMFB,” IEEE Transaction The building block, called the FD-OTA implemented by on circuits and systems-II, vol. 50, pp. 762-770, 2003. using commercially available ICs, has been introduced via [6] A. N. Mohieldin, E. S. Sinencio and J. S. Martinez, “A fully this paper. The internal construction is very simple. The balanced pseudo-differential OTA with common-mode feedforward usabilities have been verified by the simulation and and inherent common-mode feedback detector,” IEEE journal of application example. The application circuit is biquadratic solid-state circuits, vol.38, pp.663-668, 2003. low pass filter. They show good agreement as theoretically [7] M. A. Tan and R. Schaumann, “Simulating general-parameter depicted. Our future work is to find more applications of the LC-ladder filters for monolithic realizations with only transconductance elements and grounded capacitors,” IEEE FD-OTA, emphasizing on the current-mode and voltage-mode Transactions on circuits and systems, vol. 36, no. 2, pp. 299-307, applications such as signal generator, rectifier, filter and etc. February, 1989. [8] A. C. M. de Queiroz and L. P. Caloba, “Reactive loop ACKNOWLEDGMENT elimination and the use of special approximations in the design of OTA-C filters,” MWACAS 1955, vol. 2, pp. 1341-1344, 1995. The authors wish to thank Mr. Amnaj Prajong, Faculty of [9] F. A. P. Barúqui, A. Petraglia and E. Rapoport, “IC design of Agricural and Industrial Technology, Nakhon Sawan an analog tunable crossover network,” ISCAS 2005, vol. 2, pp. Rajabhat University. This work was supported in part by a 1012-1015, 2005. grant from the Research and Development Institute, Uttaradit [10] C. L. Hsu, M. H. Ho, Y. K. Wu and T. H. Chen, “Design of Rajabhat University (URU). low-frequency low-pass filters for biomedical applications,” APCCAS 2006, pp. 690-695, 2006. REFERENCES [11] J. Mahattanakul and P. Khumsat, “Structure of complex elliptic Gm-C filters suitable for fully differential implementation,” IET [1] T. K. Nguyen and S. G. Lee, “Low-voltage, low power CMOS Circuits Devices Systems, vol. 1, no. 4, pp. 275-282, August 2007. operational transconductance amplifier with rail-to-rail differential [12] P. Mongkolwai, T. Pukkalanun and W. Tangsrirat, “Current- input range,” ISCAS 2006, pp. 1639-1642, 2006. mode universal biquad with orthogonal ùo-Q tuning using OTAs,” [2] S. Koziel, R. Schaumann and H. Xiao, “Analysis and ICICS 2007, pp.1-4, 2007. optimization of noise in continuose-time OTA-C filters,” IEEE [13] X. Zhang and E. E. Masry, “A novel CMOS OTA based on Transaction on circuits and systems-I: Regular papers, vol. 52: pp. body-driven MOSFETs and it’s applications in OTA-C filters,” 1086-1094, 2005. IEEE IEEE Transaction on circuits and systems-I, vol. 54, no. 6, [3] C. Chanapromma and K. Daoden, “A CMOS fully differential pp.1204-1212, June 2007. operational transconductance amplifier operating in Sub-threshold [14] T. Y. Lo and C. C. Hung, “A 1 GHz equiripple low-pass filter region and its application,” ICSPS 2010, vol. 2, pp. 73–77, July with a high-speed automatic tuning scheme,” IEEE Transaction on 2010. very large scale integration (VLSI) systems, pp.1-7, 2009. [4] T. Y. Lo and C. C. Hung, “A 1 GHz OTA-based lo-pass filter [15] A. C. M. de Queiroz, “Balanced transconductor-c ladder filters with a high speed automation tuning scheme,” IEEE Asia solid- with improved linearity,” MWSSCAS 2009, pp. 41-45, 2009. stage conference, pp. 408-411, 2007. J. Schechtman, A. C. M. de Queiroz, and L. P. Caloba, “A high performance balanced MOS transconductor,” 36th MWSCAS, pp. 1378-1381, August 1993. © 2012 ACEEE 62 DOI: 01.IJSIP.03.01.18