A New Floating Current-Controlled Positive Resistance Using Mixed Translinear Cells

374 IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS—II: EXPRESS BRIEFS, VOL. 51, NO. 7, JULY 2004 A New Floating Current-Controlled Positive Resistance Using Mixed Translinear Cells Raj Senani, Abdhesh K. Singh, and Vinod K. Singh Abstract—A simple floating current-controlled positive resistance (CCPR) circuit based upon two mixed translinear cells realized with bipolar junction transistors has been presented. The workability of the circuit and its application in realizing a variable-bandwidth bandpass filter and a new frequency shift keying generator have been confirmed by experiments and/or PSPICE simulations based upon CA3096 and ALA400 mixed transistor arrays. The proposed floating CCPR circuit appears suitable for implementation of a variety of electronically tunable analog signal processing/generation circuits in bipolar technology. Index Terms—Analog-and-mixed-signal integrated circuits and systems, bipolar transistors, current-mode circuits, floating resistance, translinear circuits. I. INTRODUCTION OLTAGE/CURRENT controlled resistances, in both grounded and floating forms, are required in the design of a number of electronically controllable analog signal-processing/signal-generation circuits such as programmable amplifiers, filters and oscillators and a number of circuits/techniques of designing such elements in CMOS technology are known, for instance, see [1]–[5] and references cited therein. By contrast, very little has been published in the open literature on realizing such elements in bipolar technology. A class-AB grounded current-controlled- positive resistance (CCPR) circuit using a mixed translinear cell (MTC) [11] suitable for integration in bipolar technology has been presented only recently by Saaid and Fabre [6]. However, as far as is known, any floating version of the grounded CCPR (GCCPR) of [6] has not been published in the open literature yet. The purpose of this brief is to describe such a circuit. V Fig. 1. Proposed floating CCPR circuit. and a voltage follower building blocks providing infinite current controllable thereby implying that other implementation(s) of an FCCPR could be obtained by starting from alternative translinear architectures of voltage buffer (e.g., the input-base voltage buffer structure of [12, Fig. 1(b) ]). An analysis of the circuit, using the translinear principle [7] and assuming all other transistors also to be matched, shows that the currents and are given by (1) Therefore, under the assumption be approximated as , the (1) can II. PROPOSED FCCPR (2) The proposed floating CCPR (FCCPR) is shown in Fig. 1 which employs two matched MTCs composed of – – – and – – – , respectively. The remaining transistors configured as current mirrors/repeaters into the are used to inject copies of the dc bias current . The circuit is obdiode-connected transistors tained by a parallel-back-to-back connection of two translinear Manuscript received January 2, 2003; revised June 3, 2003. This paper was recommended by Associate Editor S. Espejo. R. Senani is with the Division of Electronics and Communication Engineering, Netaji Subhas Institute of Technology, New Delhi 110045, India. A. K. Singh is with the Department of Electronics and Communication Engineering, Inderprastha Engineering College, Ghaziabad 201010, India. V. K. Singh is with the Department of Electronics Engineering, Institute of Engineering and Technology, Lucknow 226021, India. Digital Object Identifier 10.1109/TCSII.2004.831381 which represents a floating positive resistance between port 1and 2 having value which is controllable by the external bias current . Note that with terminal 2 (or 1) connected to ground, the MTC – – – (or – - – ) becomes redundant and in that case [with respect to terminal 1 (or 2)], the controlled resistance becomes identical to the one in [6] and realizes a grounded CCPR of given above. value III. EXPERIMENTAL AND PSPICE SIMULATION RESULTS The working of the circuit of Fig. 1 has been verified experimentally using the CA3096 mixed transistor arrays biased 2.5-V dc and varied from 50 A–250 A. with The observed – characteristics (Fig. 2) show a linear range 1057-7130/04$20.00 © 2004 IEEE SENANI et al.: NEW FLOATING CCPR 375 Fig. 2. Experimentally observed V –I characteristics (for different values of controlling current I ) using CA3096. Fig. 4. Fig. 3. Variation of resistance with dc bias current using ALA 400 transistors. PSPICE simulated V –I characteristics using ALA 400 transistor array. of about 50 mV (p-p) with some asymmetry between first and third quadrant which is attributed to the mismatches between the transistors in the two different CA3096 chips employed. The subsequent results of the new circuit, together with those of the Saaid–Fabre circuit of [6], have been obtained from PSPICE simulations using ALA400 transistors (parameters taken from [8]) to obtain a common basis of comparison. PSPICE generated – characteristics of the circuit have been shown in Fig. 3 which reconfirm the linear range of about 50 mV (p-p). Fig. 4 shows that by varying from 0.1 A to 1 mA, the value of the realized floating resistance can be varied from 126 k to 16 , with excellent correspondence between the theoretical and simulation results. Fig. 5 shows that the % total harmonic distortion (THD) in the voltage across when the peak-to-peak magniwas changed from 100 to 500 A, is tude of input current found to vary from 0.3% to 3.6%. For the simulated value of 134 , the % THD remains less than 1% for input current as high as . From the magnitude variation of the input impedance of the circuit (Fig. 6) for A, it is found that the error in the magnitude remains less than 4% upto around Fig. 5. Percent THD as a function of peak to peak magnitude of input current for R = 130 and frequency = 100 kHz. 25 MHz. PSPICE simulations have, thus, confirmed that the performance of the proposed FCCPR is almost identical to that of the GCCPR of [6] (with both realized with ALA400). IV. COMPARISON WITH RECENTLY PROPOSED FCCPR Recently, Barthelemy and Fabre [9] have also presented a FCCPR circuit employing a new eight-transistor translinear loop formulation. The Barthelemy and Fabre circuit, is however, completely unrelated to the GCCPR of [6]. We also note that the FCCPR of [9] employs 27 bipolar junction transistors (BJTs), whereas the proposed circuit of Fig. 1 employs only 15 BJTs. We have also taken the results of Barthelemy and Fabre circuit with ALA400 transistors for the sake of comparison. It is found that the performance of our circuit is at par with that of [9] with our circuit having a slight edge in terms of better bilaterality and somewhat larger bandwidth (BW) 376 IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS—II: EXPRESS BRIEFS, VOL. 51, NO. 7, JULY 2004 Fig. 7. p Active BP filter with current-controllable BW 1=C R ; ! = 1= C C R R ). Fig. 6. Frequency response of input impedance (R realized with ALA 400 transistors. (H = 1; BW = = 130 ) with FCCR (around 45 MHz as compared to 35 MHz for the Barthelemy and Fabre circuit of [9]) due to the perfect symmetry (looking into terminal 1 and 2) and relative simplicity of our structure. Thus, the new circuit achieves a considerably reduced amount % of hardware as compared to [9] while providing a competitive level of performance. V. APPLICATIONS OF THE NEW FCCPR To demonstrate the applicability of the new FCCPR, it was to realize current-controlled BW used in place of the resistor in the CFOA-based bandpass (BP) filter (using Fabre’s gyrator [10]) shown in Fig. 7. The BW was found to be variable from 3.182 to 12 kHz by varying from 7.85–25 A. PSPICE simucould lation results shown in Fig. 8 confirm this application. also be electronically controlled by similar replacements of and/or . As another application, we present a new frequency shift keying (FSK) generator based upon the new FCCPR in Fig. 9 along with resistors and capacitors where is a new single-resistance-controlled oscillator (CFOA) whose frequency of oscillation (FO) is given by Fig. 8. Variation of the BW as a function of dc bias current I . (3) with the condition of oscillation (CO) given by (4) where is an FCCPR realizing a resistance value (5) and is composed of a fixed dc component and a slowly varying square wave current (obtained from a voltage sources through a V-to-I converter made from and . With varying from 0 to 100 A, A, was made to alternate between 10 A (low) to 110 A (high), with a frequency of 167 Hz. Thus, with k 2.103 k (to Fig. 9. New FSK generator using the proposed FCCPR. be realized by a pot, in practise), 0.01 F, 0.01 F, the circuit generates an FSK signal with frequency shifting from 46.2 kHz to 14 kHz when input alternates between low and high, and thus, an FSK signal is SENANI et al.: NEW FLOATING CCPR obtained at the output. The workability of this FSK generator and has been confirmed in PSPICE and the frequencies were found to be close to their theoretical values. Last, like [9], the new FCCPR can also be applied to realize current-controlled oscillators and a CCIII (by adding a few more BJTs). VI. CONCLUDING REMARKS A new FCCPR circuit has been presented which can be considered to be a floating version of the GCCPR of [6]. The performance of the new circuit is almost identical to that of the Saaid and Fabre circuit of [6] and compares favorably with that of the Barthelemy and Fabre circuit of [9], while using a considerably reduced % hardware than the FCCPR of [9]. Because of using only BJTs, like the circuits of [6], [9], the new circuit also is eminently suitable for integrated circuit implementation in bipolar technology (within the known limitations of p-n-p transistors in integrated circuits environment). Furthermore, like Barthelemy and Fabre FCCPR of [9], the proposed FCCPR also, when augmented with a few additional transistors, can be converted into a CCCIII. The proposed circuit is thus, expected to be useful in the design of various electronically tunable analog signal processing/signal generation circuits, some of which have been pointed out here. ACKNOWLEDGMENT This work was performed at the Analog Signal Processing Research Lab, Netaji Subhas Institute of Technology (formerly, 377 Delhi Institute of Technology) and is a modified version of an unpublished report.1 REFERENCES [1] Y. Tsividis and M. Banu, “Floating voltage-controlled resistors in CMOS technology,” Electron Lett., vol. 18, no. 15, pp. 1678–679, 1982. [2] Z. 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