Idea Transcript
International Journal of Scientific Research Engineering & Technology (IJSRET), ISSN 2278 – 0882 Volume 4, Issue 8, August 2015
CMOS Realization Voltage Differencing Transconductance Amplifier and Based Tow—Thomas Filter Dipti Singh1, Praveen Kumar2 Student of IMS Engineering College, Ghaziabad 2 Assistant Professor, ECE Department
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ABSTRACT This paper presents, a new and simple CMOS realization of VDTA is presented. And the proposed block use for the design of an electronically tunable Tow-Thomas biquad filter. The presented filter is constructed using two VDTAs, two capacitors all are grounded. This circuit simultaneously realizes Low Pass and Band Pass filter responses, without changing the circuit topology. Tow-Thomas biquad filters implemented using VDTA are simulated with PSPICE simulation using the 0.18um CMOS technology to confirm the good performance of the proposed design in the paper. Keywords - VDTA, Tow-Thomas filter CMOS Integrated circuit.
element. Our proposed filter employing two VDTAs, two grounded capacitors can simultaneously realize LP and BP biquadratic filtering function from the same circuit configuration. The proposed circuit employing minimum number of passive and active components uses no external resistors. Furthermore, no parameter matching condition is required. The Tow-Thomas [4] biquad filter is a very useful second-order function block and it is also the more popular universal filter structure. Since this structure offers several advantages such as low passive and active sensitivity performance, low component spread and good stability behavior. The Tow-Thomas biquad circuit [5,6].
II. I.
INTRODUCTION
In the decade, progress in the microelectronic area presents new circuit principles of active building blocks for fast analog signal processing and improving the properties of existing ones, such as operational tranconductance amplifier (OTA) or current conveyor (CC) [2]. Some new analog active building blocks providing the potentially in analog circuit design were and are being introduced, such as current differencing transconductance amplifier (CDTA) [3]. The voltage differencing transconductance amplifier (VDTA) is a recently introduced active element [1].The VDTA is composed of the current source controlled by the difference of two input voltages and a multiple-output transconductance gains. Therefore, the VDTA device is very suitable for electronically tunable active circuit synthesis. Another advantageous feature of the use of the VDTA as an active element is that compact structures in some applications can be achieved can be achieved easily [2,1]. Furthermore, VDTA exhibits two different values of transconductance so that there is no need to external resistors for VDTA based applications All these advantages make the VDTA an alternative choice for the implementation of voltage-mode analog signal processing circuits. This paper deals with the design of the voltage-mode biquadratic filter based on the use of the VDTAs active
DESCRIPTION OF VDTA
The VDTA element is a simple active block that consists actually of two interconnected transconductance sections. Each of them provides two independent electronically adjustable transconductances (gm1 and gm2). A number of outputs of the first and the second section varies according to the particular requirements of intended application ([1, 7−10]). The basic structure of a particular variant of VDTA active element is shown in Fig. 1a, the schematic symbol in Fig. 1b. VDTA has two voltage inputs (p and n), a small number of auxiliary high impedance ports (z+ and z−, i.e. positive and negative output of first OTA section) and positive and negative current outputs (x+ and x−). The input of the second section (OTA2) is connected directly to the z+ output of the first section (OTA1).
Fig.1–Voltage differencing transconductance amplifier (VDTA) with two independent electronically adjustable transconductances: schematic symbol.
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International Journal of Scientific Research Engineering & Technology (IJSRET), ISSN 2278 – 0882 Volume 4, Issue 8, August 2015
Outer behaviour of the VDTA element is described by the following matrix: 0
0
0
0
0
0
0
0
0 0
0 0 0 0
= 0 0
0 0
(1)
According to input terminals, an output current at Z terminal is generated. The intermediate voltage of Z terminal is converted to output currents. The new CMOS realization of the VDTA is shown in Fig.2. The introduced circuit employs two Arbel-Goldminz transconductances [11]. Input and output transconductance parameters of VDTA element in the circuit are determined by the transconductance of outputs transistors. It can be approximated as (2) (3) where gi is the transconductance value of ith transistor defined by (4) μi is (i = n, p) the mobility of the carrier for NMOS (n) and PMOS (p) transistors, COX is the gate-oxide capacitance per unit area, W is the effective channel width, L is the effective channel length and IBi is bias current of ith transistor.
and it was supplemented by the well-known structure of multiple-output current conveyor of the second generation (MO-CCII). Particular transistor dimensions are included in the Table.1. The structure has three main parts: two OTA sections and one MO-CCII. MO-CCII serves as a two-output current follower that helps to obtain the required number of outputs of the first OTA section. The transconductance of the first section is controlled electronically by current IB1and IB2 the second transconductance is also controlled electronically by current IB3 and IB4. It is obvious that the number of outputs can easily be changed according to particular requirements (in the case of OTA1 stage). Table 1.Aspects of MOS Transistor (µm/ µm) MOS M1,M2,M5,M6 M3,M4 M7,M8 M9,M11,M13-17 M10,M12,M18-M22
III.
W/L 3.6/0.36 16.64/0.36 17.16/0.36 5/1 20/1
APPLICATION EXAMPLE
The proposed circuit current-mode TT biquad filter is shown in Fig.3. The circuit consists of one Modified VDTA, two grounded capacitors. Since all the capacitors are grounded, thus the circuit is beneficial to an IC implementation. Unfortunately, most of these reported circuits suffer from one or more of following weaknesses: • Excessive use of the active and/or passive elements • Lack of electronic adjustability (tunability) • The pole frequency and quality factor cannot be tuned independently Active filters with current controllable (tunable) frequency have a wide range of applications in the signal processing and instrumentation area. New advantageous filter topologies can be realized by introducing VDTAs in the filter design that leads to current controllability of the filters.
Fig. 2 – Designed CMOS implementation of proposed VDTA active element The basic structure from Fig. 1a was the starting point for the design of the CMOS implementation of VDTA shown in Fig. 2. The transistor solution of both OTA sections was derived from the structure presented in [10] www.ijsret.org
Fig 3. Circuit diagram of TT biquadratic filter
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International Journal of Scientific Research Engineering & Technology (IJSRET), ISSN 2278 – 0882 Volume 4, Issue 8, August 2015
A single-input multiple-output Tow-Thomas filter based on VDTA configuration is shown in Figure 3 .Circuit analysis yields the following transfer functions: Circuit analysis yields the following transfer functions: (5)
(6) The resonance angular frequency and the quality factor Q of proposed Network is given by:
Fig: 5. DC transfer characteristics of Iz+,Izwith respect to voltage Vp.
=
(7.a) (7.b)
But = and as mentioned earlier. By substituting in (7) we obtain: , Where x = 1 or 2. Q = 1.
(8.a)
The PSpice simulation of proposed TT biquadratic filter has been performed with given circuit parameters: C1= C2= 1pf, bias current IB1=IB2=IB3=IB4= 20 µA and IB5=IB6=100uA. The results of low-pass (LP) and band-pass (BP) are shown in Fig.6. Cutoff frequency of BP and LP is 12.274MegaHz and cutoff frequency can changing by IB bias current or gains. Electronic Tunability of proposed filter circuit shown in Fig- 7 (a), (b).
(8.b)
It is obvious from (8.b) that quality factor Q has no sensitivity to passive components, and that gives the designer a margin of freedom in designing progress. It is clear from (7) that and Q can be electronically tuned by adjusting the bias currents of the VDTA (changing gm1 and gm2). In addition, it can be seen that the parameters and Q are orthogonally controllable by adjusting the ratio to , to or to . Sensitivity analysis of the filter parameters shows that
Fig-6. LP and BP frequency response of TT biquad circuit
Which all low.
IV.
SIMULATION RESULT
For the simulation TSMC 0.18μm CMOS Technology is used. The aspect ratios of the transistors have shown in table 1. Supply voltages are taken as VDD = −VSS = 0.9 V and IB1 = IB2 = IB3 = IB4=IB5= IB6= 100 μA biasing currents are used. Simulation results show that this choice yields transconductance values of VDTA as gm1 = gm2 = 520.868 μA/V .The DC transfer characteristic of Iz+ and Iz- against Vp for output stage of proposed VDTA is shown in Fig. 5 .
Fig-7(a). Low-pass filter peaking vs. Q by Bias current varying.
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International Journal of Scientific Research Engineering & Technology (IJSRET), ISSN 2278 – 0882 Volume 4, Issue 8, August 2015
Fig-7(b). Bandpass filter when IB current varying
V.
CONCLUSION
In this work, a new configuration for realizing TowThomas biquad filter has been proposed. By employing the VDTA the filter produces simultaneously low-pass and band-pass responses at high-output impedances, which makes the filter to be suitable for direct cascading with other current -mode circuits without additional buffer circuits. It uses only two grounded capacitors as passive elements. It permits controlling its quality factor without affecting the natural frequency. In addition, the adjustment of the natural frequency and the quality factor can be performed electronically by the biasing current of the VDTA and that adds flexibility to the tuning procedure of the circuit
Telecommunications and Control Systems and Workshops (ICUMT), 4th International Congress, 3–5 Oct. 2012, pp.484–489. [8] J. Satansup, W. Tangsrirat, Single VDTA-based current-mode electronically tunable multifunction filter, 4th International Science, Social Science, Engineering and Energy Conference (I-SEEC 2012), Petchburi, Thailand, Dec. 2012. [9] D. Prasad, D. R. Bhaskar, M. Srivastava, Universal Current-Mode Biquad Filter Using a VDTA, Circuits and Systems, 4, 1, pp. 29–33, 2013. [10] J. Satansup, T. Pukkalanun, W. Tangsrirat, Electronically Tunable Current-Mode Universal Filter Using VDTAs and Grounded Capacitors, International MultiConference of Engineers and Computer Scientists, Vol II, (IMECS 2013), Hong Kong, March 13–15, 2013. [11] ARBEL, A. F., GOLDMINZ, L. Output stage for current-mode feedback amplifiers, theory and applications. Analog Integrated Circuits and Signal Procesing, 1992, vol.2, no. 3, p. 243 – 255.
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