International Journal of Advances in Science Engineering and Technology, ISSN: 2321-9009, http://iraj.in
Vol-5, Iss-2, Spl. Issue-1 May.-2017
DOCCCII BASED MINIMUM COMPONENT MIX MODE UNIVERSAL FILTER 1 1,2
JAHARIAH SAMPE, 2MOHAMMAD FASEEHUDDIN, 3SAWAL HAMID MD ALI
Institute of Microengineering and Nanoelectronics (IMEN), 3Faculty of Engineering and Built Environment University Kebangsaan Malaysia (UKM), 43600 Bangi, Selangor E-mail:
[email protected],
[email protected],
[email protected]
Abstract- A biquadratic mixed mode tunable universal filter is presented. The mix mode filter is based on dual output second generation current controlled current conveyor (DOCCCII). The filter is capable of realizing high pass (HP), low pass (LP), band pass (BP), notch pass (NP) and all pass (AP) responses in voltage mode (VM), current mode (CM) and trans-impedance mode (TIM). In trans-admittance mode the filter can realize HP and BP responses. The filter employs only two capacitors and a single resistor and hence enjoys minimum component requirement. The resistor is required only for obtaining TIM filter response. By properly exciting the filter structure with appropriate current or voltage signals the filter response in all four modes can be obtained. The filter enjoys the ability of independent control of quality factor and filter frequency. The filter is simulated in Hspice using 0.18µm CMOS model parameters obtained from TSMC. The active and passive sensitivities for the designed filter are also low. Keywords- current mode; current conveyor; universal filter; mix mode
I. INTRODUCTION Filters are an integral part of almost every electronic system and so their synthesis and development remains an ever evolving field. Among various filter structures universal filters are the most versatile as all the standard filter functions can be derived from them [1]. They serve as standalone solution to many filtering needs. Owning to their inherent advantage of wide bandwidth, high slew rate, low power consumption, simple circuitry and excellent linearity [2-3] current conveyors (CC) are widely used in electronic design. Moreover, the requirement of low voltage low power operation put forward by portable electronic devices and the energy harvesting systems [4-5] etc. further encourages the use of CC. The current controlled current conveyor (CCCII) is the most versatile active element due to its electronically tunable parasitic resistance [6]. Numerous filter implementations utilizing CCCII can be found in the open literature [6]. The universal filter structure can be regarded as the most flexible as it can realize all the standard filter functions without any alteration in its topology. In the present day mixed mode design environment where many systems interact many times the need arises for the current mode and voltage mode circuits to be connected together. This requirement can be met by employing trans-admittance mode (TAM) and trans-impedance mode (TIM) filter structures which can serve as the interface providing distortion free interaction. Although a number of TAM and TIM filter structures can be found in the literature [7] but a single topology providing the CM, VM, TAM and TIM responses will be an added advantage in terms of area and power requirements. In the past two decades, a number of mixed mode filters have been proposed utilizing different current mode active
elements like dual output current controlled current conveyor (DOCCCII), multi output current conveyor (MOCCII) [6], current controlled current conveyor transconductance amplifier (CCCCTA) [6], Current feedback operational amplifiers (CFOA) [6], fully differential current conveyor (FDCCII) [6], differential difference current conveyor and digitally programmable current conveyor (DPCCII)[6]etc. Many reported mix mode universal structures use several active and passive elements like the one reported by Abuelma’atti et al. [9] with six CCII, one DOCCII, eight resistors and two grounded capacitors. The filter is able to realize all filter function in four modes. The same author [10] presented another mixed mode universal filter employing four DOCCCII and two capacitors. Although the active and passive elements are halved compared to the previous design but still the structure was not able to realize all pass response in any mode. Maheshwari et al. [11] proposed single input multi output (SIMO) filter employing three CCCCTAs and two grounded capacitors. The circuit is capable of realizing HP, LP and BP responses in all four modes. Additionally, the filter can realize low pass notch (LPN), high pass notch (HPN) and AP responses in CM and TAM modes of operation. Horng et al. [12] proposed a CM and TIM mode nth order filter using MOCCII realizing all standard filter functions. The filter required (n+1) MOCCII, (n+1) resistors and n grounded capacitors for realization. For the realization of second order response the filter structure would require three MOCCII, three resistors and three capacitors which will result in large area and increased power dissipation. Siripruchyanun et al. [13] proposed a CM and VM mode universal filter realizing all standard functions in both the modes. The multi input single output (MISO) structure employs two DOCCCII and two capacitors. The
Docccii Based Minimum Component Mix Mode Universal Filter 17
International Journal of Advances in Science Engineering and Technology, ISSN: 2321-9009, http://iraj.in
circuit also has the independent tuning capability. Pandey et al. [14] presented a mixed mode universal filter employing one DOCCCII, one MOCCCII, two resistors and two capacitors. The circuit is capable of realizing all the standard filter functions in the four modes with electronic tunability. But the circuit lacked uniformity as all the responses of a particular mode having same polarity cannot be obtained from a single output node. Zhijun et al. [15] proposed a SIMO universal filter capable of realizing LP, HP and BP filter responses in all four modes. The circuit utilized five MOCCCII, two grounded capacitors. Singh et al. [16] proposed a CFOA based mixed mode universal filter capable of realizing all the five generic filter functions employing only 4 CFOAs, 2 grounded capacitors and nine resistances and a switch. By properly selecting the passive elements the proposed structure can work in all four modes. The literature survey shows that the mixed mode filters employing on DOCCCII are very scarce. In this research paper the authors propose a mixed mode universal filter synthesized by two DOCCCII. The filter uses only two capacitors and a single resistor. The resistor is required only for obtaining TIM filter response. By proper excitation with appropriate current or voltage signals the filter structure can perform in all four modes. The filter is capable of realizing high pass (HP), low pass (LP), band pass (BP), notch pass (NP) and all pass (AP) responses in voltage mode (VM), current mode (CM) and trans-impedance mode (TIM). In transadmittance mode the filter can realize HP and BP responses.
Fig. 1: Block diagram of DOCCCII
The CMOS implementation of a class AB DOCCCII is presented in Fig. 2. The circuit consists of a translinear loop (transistors M1 – M4). Two current mirrors (transistors M5 – M6 and M7 – M8) are used to bias the translinear loop with bias current I , the input cell presents a high impedance at voltage input node Y and a low input impedance at current input node X. This cell acts as voltage follower. The current at node X is copied to output nodes Z+ and Z–. The cross coupled current mirrors are used to generate negative current at Z- node.
II. CMOS IMPLEMENTATION OF DUAL OUTPUT CURRENT CONTROLLED CURRENT CONVEYOR The concept of the CCCII is similar to that of CCII with an exception that it has a tunable parasitic resistance at the X terminal which is tunable via bias current. This makes CCCII superior in design than CCII since it requires no external resistance for activation [8]. The V-I relationship of the CCCII is presented in the matrix (1) and the block diagram is shown in Fig. 1. V I I
R 1 0 I 0 0 0 V (1) ±1 0 0 V 1 R = (2) g +g
Where β = µ C MOS transistor.
Vol-5, Iss-2, Spl. Issue-1 May.-2017
Fig. 2: CMOS implementation of DOCCCII [8]
III. THE PROPOSED MIXED MODE FILTER The proposed mixed mode MISO type universal filter consists of only two DOCCCII, two capacitors and a single resistor as presented in Fig. 3. The resistor is needed only for obtaining TIM response for VM, TAM and CM responses it is not required so this make it a minimal component realization. The filter is capable of realizing all five generic filter functions in VM, CM and TIM mode and HP, BP in TAM mode.
is the physical parameter of the
Fig. 3: Proposed Mixed Mode Universal Filter
Docccii Based Minimum Component Mix Mode Universal Filter 18
International Journal of Advances in Science Engineering and Technology, ISSN: 2321-9009, http://iraj.in
Vol-5, Iss-2, Spl. Issue-1 May.-2017
In voltage mode operation all the currents I , I , I and I are set to zero. The output is obtained from V node. The analysis of the filter leads to the following transfer function. V = (3) From (3) it can be deduced that by properly selecting input voltages V , V and V all the responses can be obtained. The input sequence to be applied is given in Table I. For realizing AP function V must be twice of the other two input currents. To accomplish this voltage amplifier with gain equal to two is needed.
TABLE III: INPUT SEQUENCE FOR TRANS-IMPEDANCE MODE OPERATION
I
= (
)
(6)
The complete input application sequence is presented in Table IV.
TABLE IV: INPUT SEQUENCE FOR TRANS-ADMITTANCE MODE OPERATION
TABLE I: INPUT SEQUENCE FOR VOLTAGE MODE OPERATION
In current mode operation the voltages V , V and V are reduced to zero and the input currents I , I and I are applied as per Table II to obtain the five standard responses. In CM only three current inputs are required the current I is not needed. The analysis of the filter under the above mention conditions yields the following transfer function. The output is obtained from I node. I
Q =
(7)
ω =
=
The quality factor Q, natural frequency ω and bandwidth of the filter are given in (7-9). It can be inferred from the expressions that by changing the bias currents while keeping their ratio constant. The Q and ω of the filter can be tuned independently.
(
)
(8)
(4) BW =
=
(9)
IV. SIMULATION RESULTS
TABLE II: INPUT SEQUENCE FOR CURRENT MODE OPERATION
In trans-impedance mode the input will be current and the output will be voltage. In TIM three input currents are required namely I , I and I while the currentI is not required. Proper application of currents as stated in Table III will lead to the realization of the standard filter functions. The complete transfer function of the TIM mode filter is presented in (5). The output in this case is obtained across the resistor R (V ). V
To establish the workability of the proposed filter structure it was examined using H-Spice. The DOCCCII was designed and simulated using 0.18µm TSMC CMOS technology parameters. The supply voltage used is ±1.5V and the bias current was set at 20µA.The aspect ratios of the transistors are given in Table V.
= (
)
(5)
In trans-admittance mode only two functions are realizable namely HP and BP. The transfer function for TAM mode is given in (6).
TABLE V: ASPECT RATIOS OF THE TRANSISTORS
The proposed mixed mode filter is tested at a bias current of 20µA. The values of the capacitors are set at C1=C2=250pF leading to quality factor of one. The
Docccii Based Minimum Component Mix Mode Universal Filter 19
International Journal of Advances in Science Engineering and Technology, ISSN: 2321-9009, http://iraj.in
Vol-5, Iss-2, Spl. Issue-1 May.-2017
parasitic resistances R and R of the two DOCCCII are 796.063Ω for the specified bias current. At first the universal filter structure is simulated to validate the VM operation followed by CM and TIM operation. The Fig. 4 presents the responses for the VM filter. The Fig. 5 gives the phase response of the VM AP filter. The CM mode responses of the filter are given in Fig. 6. The CM AP filter phase is presented in Fig 7. The TIM filter responses are given in Fig. 8 and the phase response of the filter is shown in Fig.9. Fig. 7: Phase of the all pass current mode filter
Fig.8: Trans-impedance mode response of the mixed mode universal filter
Fig. 4: Voltage mode response of the mixed mode universal filter
Fig. 5: Phase of the all pass voltage mode filter Fig. 9: Phase of the all pass trans-impedance mode filter
To further validate the signal processing capability of the filter a time domain analysis was performed for the CM, VM and TIM modes. A sinusoidal signal of 800mV p-p is applied at a frequency of 10MHz and the HP response of the VM filter is noted as given in Fig. 10. For CM and TIM filters a sinusoidal signal of 80µA p-p is applied at a frequency of 10MHz and 1 kHz.
Fig.6: Current mode response of the mixed mode universal filter
The current mode HP and trans-impedance mode LP responses are monitored Fig. 11-12. The analysis reveals that the filter operates with minimum distortion and hence suitable for mixed mode signal processing.
Docccii Based Minimum Component Mix Mode Universal Filter 20
International Journal of Advances in Science Engineering and Technology, ISSN: 2321-9009, http://iraj.in
Vol-5, Iss-2, Spl. Issue-1 May.-2017
The tunability of the proposed filter is examined by observing the voltage mode LP response for three different bias currents of 20µA, 100µA and 150µA. It can be seen from Fig. 13 that the frequency of the filter increases with increment in the bias current. This proves the tunability of the filter structure. V. SENSITIVITY ANALYSIS
Fig.10: Time domain analysis of the HP output of the voltage mode filter
As a result of component tolerance and non-idealities in CCII the response of the practical filter deviates from the ideal one. To get a measure of the deviation, the concept of sensitivity is employed [17]. The passive sensitivities of ω and Q of the proposed dual mode multifunction filter are: 1 S =S =S =S =− 2 S
=S S
=− = S
=
The inspection shows that all the passive sensitivities of the filter are low. CONCLUSION Fig.11: Time domain analysis of the HP output of the current mode filter
Fig.12: Time domain analysis of the LP output of the transimpedance mode filter
In this paper a second order biquadratic mixed mode universal filter is proposed. The filter can perform in four modes namely VM, CM, TIM and TAM. The filter enjoys requirement of minimum components only two DOCCCII, two capacitors and a grounded resistor. The resistor is required to obtain the TIM output and so it can be omitted if TIM response is not required. The utilization of DOCCCII removed the requirement of external resistors. By proper excitation the filter is capable of realizing HP, LP, BP, NP and AP response in VM, CM and TIM mode. The HP and BP responses can be obtained in TAM mode of operation. The filter frequency and quality factor can be independently tuned via bias current. The filter enjoys low active and passive sensitivities. ACKNOWLEDGMENT The authors gratefully acknowledge the support provided by UKM internal grant (GUP-2015-021) and grant from ministry of education (FRGS/2/2014/TK03/UKM/02/1) for this study. REFERENCES [1]
[2] Fig.13: The change in filter frequency with variations in biasing current
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