511-516A new CMOS based current follower (CF) with externally controllable X terminal intrinsic resistor has been proposed in this manuscript. Also, a new electronically tunable grounded inductor simulator using only a grounded capacitor has been proposed. The inductor simulator does not need any external resistors. It can be tuned electronically by changing a control voltage. However, it has a single active component matching condition. The simulations results are given in order to demonstrate the performance of the circuits

Alpaslan, Halil

Yuce, Erkan

English

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Indian Journal of Pure & Applied Physics Vol. 54, August 2016, pp. 511-516       New CMOS based current follower and its applications to inductor simulator and band-pass filter Halil Alpaslan & Erkan Yuce* Electrical and Electronics Engineering, Pamukkale University, Kinikli, 20070, Denizli, Turkey Received 27 August 2013; revised 7 April 2014; accepted 25 September 2014 A new CMOS based current follower (CF) with externally controllable X terminal intrinsic resistor has been proposed in this manuscript. Also, a new electronically tunable grounded inductor simulator using only a grounded capacitor has been proposed. The inductor simulator does not need any external resistors. It can be tuned electronically by changing a control voltage. However, it has a single active component matching condition. The simulations results are given in order to demonstrate the performance of the circuits. Keywords: Current follower, Voltage follower, Inductor simulator, Band-pass filter 1 Introduction The use of current-mode (CM) active devices such as second-generation current conveyors (CCIIs) has some potential advantages for example greater dynamic range, wider bandwidth, etc. when compared to their voltage-mode (VM) counter parts for instance operational amplifiers (OAs)1-3. Nevertheless, CCIIs have both  non-ideal current gain and voltage gain effects which restrain some circuit performance properties such as slew rate, bandwidth and dynamic ranges4-15. Therefore, the active devices known as voltage followers (VFs) and current followers (CFs) can be preferred to design of analog integrated circuits (ICs) instead of CCIIs in order to avoid both non-ideal gains effects. Besides, design of analog circuits with CFs and VFs can provide more simplicity and more performance such as wider bandwidth, lower power consumption. A VF has only non-ideal voltage gain effects while a CF has only non-ideal current gain effects. A number of analog circuits such as oscillators4,5 a negative impedance converter (NIC)6,analog filters7-21and some simulated inductors22-54 using various active devices have been presented from past to present in open literature. However, the presented simulated inductors suffer from one or more of the following drawbacks:  (i) Complex internal structure22,31,34,37,38,41,43,44,48-54 (ii) External passive resistors22,24-26,29-37,40,43,44,46-54 (iii) Excessive number of active device23-27,29,32,35 (iv) Lack of electronically controllability24-26,29-40,43-51 (v) OAs42 (vi) Floating capacitors27,30,31,33,34,36,37,40,42-44,46,49-51  In this paper, a new CMOS based voltage controlled dual output CF (VCDO-CF) with X terminal intrinsic resistor and a new electronically tunable grounded inductor simulator are proposed. The inductor simulator is composed of a VCDO-CF and a simple voltage controlled VF (VCVF) with externally controllable X terminal intrinsic resistor. Furthermore, it does not require any external passive resistors. In other words, the inductance value of it can be adjusted externally by changing a control voltage. Also, it employs a grounded capacitor; thus, it is suitable for integrated circuit fabrication52-54. Nonetheless, it needs a single active element matching constraint. The simulation results are given to demonstrate the performance of the grounded inductor simulator and its band-pass filter application.  2 Proposed Current Follower and Simple Voltage Follower In non-ideal conditions, the matrix equations for a VCDO-CF and a VCVF are given as, respectively:  0 00 00 0X XXZ ZZ ZV IRI VI Vαγ+ +− −        =        −     … (1a)  0 0Y YX X XI VV R Iβ     =           … (1b)  It is seen from Eq. (1) that α is non-ideal current gain of the Z+ terminal of the VCDO-CF, γ is  ————— *Corresponding author (E-mail:erkanyuce@yahoo.com) INDIAN J PURE & APPL PHYS, VOL 54, AUGUST 2016   512 non-ideal current gain of the Z- terminal of the VCDO-CF, β is non-ideal voltage gain of the VCVF and RX is the X terminal intrinsic resistor of the VCDO-CF and VCVF. In ideal conditions, current gain of the Z+ terminal of the VCDO-CF and voltage gain of the VCVF are equal to unity. Also, current gain of the Z-terminal of the VCDO-CF is equal to two. The symbolic representation of the VCDO-CF and VCVF are shown in Figs 1(a) and 1(b), respectively.  Internal structure of the proposed VCDO-CF is shown in Fig. 2 and internal structure of a simple VCVF55 is depicted in Fig. 3. Dimensions of the proposed VCDO-CF are given in Table 1. Also, aspect ratios of the PMOS transistors of the simple VCVF are chosen as (W/L)1=(W/L)2=24µm/0.75µm.   All the MOS transistors are operated in saturation region. Also, all the bulks are connected to relevant sources. Transconductances of the NMOS and PMOS transistors are gmN and gmP, respectively. Further, output conductances of the NMOS and PMOS transistors are gdsN and gdsP, respectively. It is assumed that transconductances of all the PMOS and NMOS transistors much greater than their corresponding output conductances (gmN,P>>gdsN,P). Some assumptions are performed for the proposed VCDO-CF as follows:  1 2 5 7 869 10 1415.........2.........2mM mM mM mM mM mPmM mPmM mM mM mNmM mNg g g g g gg gg g g gg g= = = = = === = = ==  … (2)   Similarly, some assumptions are performed for the simple VCVF as 1 2mM mM mPg g g= = . Consequently, X terminal intrinsic resistor of both VCDO-CF and VCVF are found as:  1XmPRg≅  … (3)  Transconductance of the PMOS transistor can be calculated as:   2( )mP P ox DD C TPPWg C V V VLµ  = − −   … (4)   Fig. 1 — (a) VCDO-CF representation (b) VCVF representation    Fig. 2 — The proposed CMOS based VCDO-CF  Table 1 —Transistor sizes of the proposed VCDO-CF in Fig. 2 Transistor type Transistors W (µm) L (µm) M1-M5, M7-M8 24 0.75 PMOS M6 48 0.75 M9-M14 50 3 NMOS M15 100 3  ALPASLAN & YUCE: CMOS BASED CURRENT FOLLOWER AND ITS APPLICATION   513 where µP is hole mobility, Cox is oxide capacitance, (W/L)P is transistor aspect ratio of PMOS, VTP is threshold voltage of PMOS, VC is control voltage and VDD is positive power supply voltage56.     3 The Simulated Inductor and VM Band-pass Filter Application Impedance of the proposed inductor given in Fig. 4 can be computed as: 1 2 1 2inin X X X XinVZ sCR R R RI= = + −  … (5)  In Eq. (5), if RX1 = RX2 is selected, the impedance of the proposed inductor simulator turns to: 1 2 2in X XmPsCZ sCR Rg= = … (6)  The impedance of the proposed inductor including non-ideal gain effects is evaluated as:  1 2 1 2 (1 )X X X XinsCR R R RZ γαβ+ + −=  … (7)  In Fig. 5, a VM band-pass (BP) filter with passive circuit elements is shown. The proposed simulated inductor is replaced instead of the passive inductor to examine performance and workability. Transfer function of the BP filter is given as in the following:  211 1f foutinf f fsC RVVs sC R LC=+ + … (8)  Quality factor (Q) and angular resonance frequency (ω0) are respectively found as follows:  ffCQ RL=  … (9a)  01fLCω =  … (9b)  4 Simulation Results 0.25 µm standard CMOS technology parameters57 with ±1.25V symmetrical DC power supply voltages are used in all the simulations. The MOS internal structures of the VCDO-CF and VCVF respectively shown in Figs 2 and 3 are used in all simulations. DC current transfer characteristic of the VCDO-CF in accordance with control voltage is given in Fig. 6. The VCDO-CF   Fig. 3 — Simple VCVF55    Fig. 4 — The proposed grounded inductor simulator employing a grounded capacitor   Fig. 5 — VM band-pass filter realization with R, L and C components    Fig. 6 — DC output current of the VCDO-CF changes with respect to control voltages and input currents INDIAN J PURE & APPL PHYS, VOL 54, AUGUST 2016   514 operates properly between 80 µA and 120 µA. Also, X terminal intrinsic resistor values of each of the VCDO-CF and VCVF can be changed between 1.66 kΩ (VC = 0.34 V) and 2.1 kΩ (VC = 0.44 V) by adjusting control voltages as illustrated in Fig. 7. In Fig. 8, the tunability of the proposed grounded inductor simulator with VC and C is given. C=100 pF, Rf  =20 kΩ and Cf =12.2 pF are chosen in all the simulations below. Not only center frequency (f0) but also Q and bandwidth (BW) change with VC as indicated in Table 2. Total power dissipation changes versus VC are given in Fig. 9. It is observed from Fig. 9 that as the control voltage increases, power dissipation decreases. f0 of the VM BP filter changes with VC as shown in Fig. 10.  VC=0.4 V is used in all the following simulations. In Fig. 11, gains of an ideal BP filter and a non-ideal BP filter are given. The total harmonic distortion (THD) changes for the VM BP filter versus applied peak sinusoidal input signals are given in Fig. 12. It is seen from Fig. 12 that THD values are low enough. The input and output noise changes of the VM BP filter is given in Fig. 13. Monte Carlo (MC) analysis for 100 runs is performed by changing 25% of Cf values of the BP filter. Simulation results for the center frequency of the BP filter related with MC analysis are given Fig. 14. About 700 kHz change in f0 can be observed from Fig. 14.   Fig. 8 — Phase and magnitude of the impedance of the proposed inductor simulator with VC and C against frequency   Table 2 — f0, Q and bandwidth change with control voltages  VC = 0.38 V VC = 0.4 V VC = 0.42 V VC = 0.44 V f0 (MHz) 2.85 2.75 2.66 2.57 Q 3.34 3.55 3.69 3.73 BW (kHz) 851 775 720 688    Fig. 7 — X terminal intrinsic resistors of the VCDO-CF and VCVF with respect to control voltage ALPASLAN & YUCE: CMOS BASED CURRENT FOLLOWER AND ITS APPLICATION   515 It is important to note that ideal and simulation results are close to each other but the difference between them arises from frequency dependent non-ideal gains and parasitic impedances of the VCDO-CF and VCVF.    Fig. 12 — Total harmonic distortion variation against peak values of sinusoidal input signals     Fig. 13 — Input and output noise changes vs frequency    Fig. 14 — MC analysis of the VM BP filter    Fig. 9 — Total power dissipation changes vs control voltage    Fig. 10 — Gain change with control voltage vs frequency    Fig. 11 — Ideal and simulated BP filter gains with respect to frequency  INDIAN J PURE & APPL PHYS, VOL 54, AUGUST 2016   516 5 Conclusions In this work, a new CMOS based VCDO-CF is proposed. Furthermore, a new electronically tunable grounded inductor simulator by using the VCDO-CF and a simple VCVF is proposed. The inductance value of the grounded inductor simulator can be adjusted externally by changing a control voltage. Also, it employs a grounded capacitor; thus, it is suitable for integrated circuit fabrication. Nonetheless, it needs a single active element matching constraint. The simulation results verify the claimed theory well.  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New CMOS based current follower and its applications to inductor simulator and band-pass filter

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New CMOS based current follower and its applications to inductor simulator and band-pass filter

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