A CMOS Multi-Output Cross-Coupled Gain-Boosting Current- Mode Integrator

Transcription

1 Vol.6, No.6 (203), pp A CMOS Multi-Output Cross-Coupled Gain-Boostin Current- Mode Interator Junho Ban, Inho Ryu, Jeho Son, Hyunjun Chun IT Applied System Enineerin, Chonbuk National University, 567 Baekje-daero, deokjin-u, Jeonju-si, Jeollabuk-do , Korea Telephone: , Fax: , toto00@jbnu.ac.kr Abstract In this paper, a cross-coupled ain-boostin current-mode interator is proposed, which is better than typical current mirror interator when compared in terms of increasin ain and frequency response. The results of small sinal equivalent circuit analysis and HSPICE simulation of the proposed interator show that ain and frequency response is improved at supply voltaes of V band. An example application usin the proposed interator lowvoltae current-mode filter is also presented. The simulated cutoff frequency of the desined filter is 200MHz at a supply voltae of.8v. Keywords: Current-mode, Interator filter. Introduction Current mode circuit is bein widely used in analo sinal processin includin broadband communication systems. When it is compared with voltae mode circuit current mode circuit can reduce the element s overlappin, and since it uses current feedback the impedance output node which is unfavorable in the low-voltae circuit can be removed. Because of this special feature the analo filter desin which needs lowvoltae supply can be benefited [-9]. So far, many realizations of voltae and current mode filters have been reported [0-5]. Accordin to these researches, current mode filter usin interator shows the use of low supply voltae about V power supply voltae which is relatively less than the existin voltae mode usin active RC interator, Gm-C interator which needs voltae supply of 2.5~3.3V. Current mode interator which is the core circuit of current mode filter, and as an important desin parameter which decides performance of the current mode interator are hih current amplifyin ain, wide frequency bandwidth, low input impendence and hih output impendence In Reference [7] current mirror type current mode interator of differential input sinle output type was desined and in reference[8] this structure was desined to fully differential structure from which noise of the current mode interator was reduced and at the same time bandwidth was increased. In addition to that, in reference [9] current mode interator input circuit is composed of cascode circuit and current mode interator s output impedance is increased. In this paper, we analyzed the ISSN: IJCA Copyriht c 203 SERSC

2 Vol.6, No.6 (203) characteristics of these circuits researched and presented until recently, and we propose a new current mode interator. In Chapter 2, we analyzed the characteristics of typical current mode interator and proposed a new current mode interator which is composed of cross-coupled ain-boostin circuits, and we compared the characteristics between the typical interators and the proposed interator. In Chapter 3, a current mode lowpass filter is desined as the application of the proposed current mode interator and the possibility of application is checked and concluded in Chapter4. 2. Desin of a New Cross Coupled Gain-boostin Current Mode Interator By usin advantaes of current mode circuit with hih frequency response as lowvoltae supply and low power consumin response, a current mode interator of current mirror type which is composed of current mirror as input and output topoloy has been used in analo sinal processin circuits widely [7]. And in order to brin safety from noise, fully differential current mode interator of current mirror type was desined in Reference [8]. The fully differential current mode interator of current mirror type is shown in Fiure (a) and small sinal equivalent circuit to analyze the ain and frequency response is shown as Fiure (b). (a) (b) Fiure. (a) Fully-balanced current-mirror current-mode interator, (b) Small sinal equivalent circuit 40 Copyriht c 203 SERSC

3 Vol.6, No.6 (203) Transistors, M, M2 and M3 distinuished as part a and b are shown as fully balanced structure, and the transistor size of M4, M5 and M6 area equal and it is desined to have operatin voltae, so for the analysis of small sinal, only from the half circuit usin KCL () and (2) can be derived. sc ) sc ( ) i () ( m ds// 4 d 2 m3 ds 3// 6 scd( 2 2 ) i (2) The m, ds are transconductance and output conductance, and C d and C are capacitance between ate and drain of M2 and capacitance connected to interator s input terminal, respectively. Combinin () and (2), we find transfer function as (3) and each parameter can be calculated. The pole and output resistance are equal to (5). in out i k( s z ) (3) in i out ( s p)( s p2) p m ds (4) C r o (5) 2 Also current ain is equal to (6), and unit ain frequency is calculated with (7). m3 ds 3 A (6) m ds m3 ds 3 o p A (7) C Input resistance of ideal current mode circuit is zero and output resistance must be infinite. Also current ain and unit ain frequency of ideal current mode circuit should be infinite. But when desinin real interator the ideal characteristics cannot be satisfied. However desinin current mode interator with bi value current ain and unit ain frequency is reducin the errors which can occur as much as possible. To increase current ain in current mode circuit of current mirror type in Fiure, Reference [9] used a cascode circuit as shown in Fiure 2 which is method for increasin output resistance resultin increment in current ain. But, the cascode circuit cannot be used in the desin of low-voltae circuit. In Fiure 2, in the cascode type current mirror, in the condition of securin rane in order to move all circuits to saturation reion required DC supply is 2 +V THn.. At this if we ive value to input-output operatin voltae rane as V, for saturation minimum drain-source voltae is shown as as 0.25V and throuh NMOS threshold voltae V TH as 0.5V, all required voltae supply is 2V. As a result, the cascode type current mirror shown in Fiure 2 is unfavorable to desin low-voltae circuits with V supply voltae. ds3 ds6 ds Copyriht c 203 SERSC 4

4 Vol.6, No.6 (203) Fiure 2. The cascode current-mirror current-mode interator 2.. Proposal for cross coupled ain-boostin current mode interator In this paper, a new improved CMOS confiuration of current mode interator is presented as shown in Fiure 3 providin hih unity ain frequency and current ain compared to current mirror of Fiure and cascode type current circuit of Fiure 2. Amon the small sinal analysis results of current mirror type interator in Fiure unity ain frequency (ωo) is shown in equation (7). When observin equation(7) there is the method of expandin unity ain frequency throuh increasin transconductance, m3 and output conductance, ds3 of M3 or decreasin capacitance, C of interator. In the method, for decreasin capacitance, C of interator can cause to chane interator s time constant, t and distort also cut-off frequency of filter usin the interator. So we use a method increasin transconductance, m3 and output conductance, ds3 of M3 to expand unity ain frequency which can also increase current ain from equation (6). The proposed circuit as shown in Fiure 3 is a cross coupled ain-boostin current mode interator so as to simultaneously increase current mode ain and unit ain frequency by increasin transconductance. Fiure 3(a) is the proposed cross coupled ain-boostin current mode interator and Fiure 3(b) is the small sinal equivalent circuit of Fiure 3(a). As shown in Fiure 3, the output of the proposed interator is desined in different format. Output value of interator feedback throuh two cross-coupled feedback loops which carry the value of A, and the cross-coupled feedback loops are constructed as M4 and M8 in the Fiure 3(b). By usin the cross-coupled feedback loop the transconductance of the interator will increase as A m. We analyze this throuh small sinal circuit in the Fiure 3(b). First, the proposed cross-coupled ain-boostin current-mode interator s feature is analyzed in the same round as the analysis of typical current mirror type interator as in Fiure. 42 Copyriht c 203 SERSC

5 Vol.6, No.6 (203) (a) (b) Fiure 3(a). The proposed cross-coupled ain-boostin current-mode interator (b) Small sinal equivalent circuit The proposed interator was made as fully symmetric in structure and each transistor matched on the same size. If KCL is used only on the half part of the circuit we can et (8) and (9). From (8) and (9), the pole can be obtained as (0). ( m ds // 5 sc ) scd( 2 m3 ds 3// 7 2 A m7 2 scd( 2 ) i (8) ) i (9) p in out m ds (0) C Also current ain can be calculated as in () and unity ain frequency can be calculated as in (2). m3 ds 3 A m7 A () m ds m3 ds 3 A m7 o p A (2) C Copyriht c 203 SERSC 43

6 Vol.6, No.6 (203) The ain and frequency response of the proposed cross-coupled ain-boostin currentmode interator is compared with those of the typical current mirror type current mode interator as shown in Table. Table. The ain and frequency of the proposed cross-coupled ain-boostin interator Type Parameter Pole, p Gain, A Unity ain frequency, O The fully-balanced current-mirror currentmode interator [8] m m3 m C ds ds3 ds The proposed cross-coupled ain-boostin interator m3 m m C ds3 m3 ds3 m3 ds3 C C ds A ds A m7 m7 From Table we can confirm that the current ain and unity ain frequency of the proposed cross-coupled ain-boostin current mode interator can be increased each of them by A m /( m + ds ) and A m /C. These are the results which are obtained as mentioned before from the construction of output side from cross-coupled feedback circuit. Likewise result of small-sinal analysis simulated throuh HSPICE had the result iven in Fiure 4. Fiure 4. The HSPICE simulation results of the proposed cross-coupled ainboostin interator When HSPICE simulation was done of same simulation parameter and transistor size, the current ain and unity ain frequency of the proposed cross-coupled ain-boostin current mode interator was 38.dB and 225MHz respectively while those of the typical current mode type interator had 3.4dB and of 28MHz. Throuh these results it is conformed that 44 Copyriht c 203 SERSC

7 Vol.6, No.6 (203) the proposed cross-coupled ain-boostin interator can improve ain and frequency response of the typical interator. Another special feature of the proposed cross-coupled ain-boostin current mode interator is to be run in low-voltae. In case of the proposed current mode interator 2 supply voltae is required in order to move every circuit to saturation reion in the state of securin operatin rane of input-output sinal. With input-output operatin rane of V and overdrive voltae ( ) of 0.25V and threshold voltae (V THn ) of 0.5V, the overall supply voltae is required as.5v. The result of this special feature is only use of V THn while cascode type circuit uses 2 +V THn. Of course the value may be adjusted accordin to process parameters and desin specifications but with the same conditions minimum voltae supply of V THn can be lowered and it is favorable even in low-voltae circuit as supply voltae can be applied on V band. 3. A Current-mode Low-voltae LPF Filter In this chapter the proposed cross-coupled ain-boostin current mode interator is used to desin an active filter havin supply voltae of.8v and cutoff frequency of 200MHz. Accordin to the desin specifications (3 rd, fc=200mhz, ripple db), passive filter circuit is desined at first and then in order to convert to active filter sinal flow raph was drawn. And throuh sinal flow raph the block diaram of the 3rd-order low-pass active filter was drawn, and finally the active filter was confiured by the block diaram. Fiure 5. The current-mode 3rd passive filter First, accordin to the desin specifications the desined current mode 3 rd passive low-pass filter is shown in Fiure 5. Each of the current mode passive filter s element value is R in =R out =Ω, C=2.260F, L2=.0883H, C3=2.260F, respectively. In order to convert current mode passive filter in Fiure 5 to current mode active circuit the sinal flow raph is drawn as shown in Fiure 6. Current and voltae equation in the element of current mode passive filter made of L and C can be shown in (3), (4) and (5), respectively. V ( I s I I 2 ) (3) SC Copyriht c 203 SERSC 45

8 Vol.6, No.6 (203) I ( V 3) (4) SL V 2 V ( I 2 0 ) (5) SC I 3 3 Fiure 6. Sinal flow raph (SFG) of the passive filter Throuh the sinal flow raph in Fiure 6, the block diaram of 3 rd order current mode lowpass filter is completed as shown in Fiure 7. Fiure 7. Block diaram of the 3rd-order low-pass active filter In Fiure 7, three block of low-pass filters are substituted by 3 interator, at this time output of first stae and second stae is two-port and output of the third stae is three-port. In other words, the output of the current mode interator should be made of two-port and threeport, respectively. The proposed cross-coupled ain-boostin interator is possible to increase the number of outputs as needed which can be applied easily to multi-output construction circuit. Finally the multi-output architecture of the proposed cross-coupled ain-boostin interator is shown in Fiure Copyriht c 203 SERSC

9 Vol.6, No.6 (203) Fiure 8. Multi-output architecture of the proposed cross-coupled ainboostin interator The proposed multi-output cross-coupled ain-boostin interator was simulated usin HSPICE Usin CMOS 0.8 μm desin parameter. The chanin cutoff frequency of the filter is invested by adjustin terminal voltae inside of the interator and the results were shown in the Fiure 9 and Table 3. Fiure 9. The frequency response of the desined 3rd-order low-pass active filter Table 2. The result of the desined low-pass active filter Parameter Simulation results Copyriht c 203 SERSC 47

10 Vol.6, No.6 (203) Function of filter Type of filter Pass band ripple Low-pass 3rd Chebyshev Ladder double-terminated RC passive db Control voltae 0.66V ~.25V Gain of filter Cutoff frequency(fc) Power supply voltae -7.dB ~ -7.68dB 4MHz ~ 23MHz.8 V 4. Conclusion A cross-coupled ain-boostin current mode interated is proposed in this paper The proposed method does not use cascode method which is unfavorable in low-voltae circuit but uses cross-couplin ain-boostin formation to increase interator s transconductance by providin neative feedback on output side. After analyzin small sinal equivalent circuit and comparin the analyzed results, transconductance of the proposed interator ot increased and finally ain and frequency response ot improved. Also simulation result throuh HSPICE show that ain and unity frequency of typical current mirror type interator was 3.4dB and 28MHz, but those of the proposed cross-coupled ain-boostin current mode interator was 38.dB and 225MHz, respectively. These results confirmed that the proposed cross-coupled ain-boostin current mode interator is to be beneficial circuit which can improve ain and frequency response more than typical current mirror type interator and even in the use of low-voltae circuit of v band. In addition to that, to confirm the applicability of the proposed interator low-voltae current mode filter of.8v 200MHz bandwidth was desined. When voltae was adjusted from 0.66V to.25v, the cut-off frequency of the filter was 4MHz to 23MHz. Throuh these results, the proposed crosscoupled ain-boostin current mode interator in this paper could be used in filter desin carryin low-voltae supply. References [] C. Toumazou, F. J. Lidey and D. G. Haih, "Analoue IC desin : the current-mode approach", IEEE Circuits and systems series 2, Peter Pererinus Ltd., on behalf of the Institution of Electrical Enineerin, London, United Kindom, (993). [2] R. H. Zele and D. J. Allstot "Low-Power CMOS Continuous-Time Filter", IEEE J. Solid-State Circuits, vol. 3, no. 2, (996), pp [3] G. Ferri and N. C. Guerrini, Low-Voltae Low-Power CMOS Current Conveyors, London Kluwer Academic Publishers, (2003). [4] Y. S. Hwan, J. J. Chen, J. H. Lai and P. -W. Sheu, Fully differential current-mode third-order Butterworth VHF Gm-C filter in 0.8 lm CMOS, IEE Proc.-Circuits Devices Syst., vol. 53, no. 6, (2006). [5] N. Herencsar and K. Vrba, "Tunable Current-Mode Multifunction Filter Usin Universal Current Conveyors", icons, Third International Conference on Systems (icons 2008), (2008), pp. -6. [6] C. C. Hsu and W. S. Fen, Structural eneration of current-mode filters usin tunable multiple-output OTAs and rounded capacitors, IEICE Transactions on Fundamentals, vol. E83-A, (2000), pp [7] S. S. Lee, R. H. Zele, D. J. Allstot and G. Lian, "A continuous-time current-mode interator", IEEE Trans. Circuits and Systems, vol. 38, (99), pp Copyriht c 203 SERSC

11 Vol.6, No.6 (203) [8] R. H. Zele, D. J. Allstot and T. S. Fiez, "Fully-differential CMOS current-mode circuits", in Proc. IEEE ISCAS, (992), pp [9] P. Mandal and V. Visvanathan, "A self-biased hih performance folded cascode Op-Amp", IEEE 0th International Conference on VLSI Desin, (997), pp [0] H. Kouara, H. Laib and A. Chahi, A New Method to Extract Reference Currents for Shunt Active Power Filter in Three Phase Four Wire Systems, IJAST, vol. 46, (202) September, pp [] Y. C. Yoo and K. H. Eom, A Study on the Desin of Coaxial Isolator with Filter Circuit, IJFGCN, vol. 4 no. 3, (20), pp [2] J. L. Narayana, K. S. R. Krishna, L. P. Reddy, G. V. Subrahmanyam and M. Sindhu, Hih Dimensional Modelin of Microstrip Hairpin Bandpass Filter Usin Artificial Neural Networks, IJFGCN, vol. 5, no., (202), pp. -4. [3] M. Chakraverty, S. Mandava and G. Mishra, Performance Analysis of CMOS Sinle Ended Low Power Low Noise Amplifier, IJCA, vol. 3, no. 2, (200), pp [4] H. S. Yazdi and F. Homayouni, Impulsive Noise Suppression of Imaes Usin Adaptive Median Filter, IJSIP, vol. 3, no. 3, (2009), pp. -2. [5] P. Maffezzoni, Stochastic Analysis of Switched-Capacitor Circuits for Sampled Data Converters, IEEE Trans.on Computer-Aided Desin of Interated Circuits and Syatems, vol. 3, no. 3, (202), pp Authors Jun-Ho Ban He received the B.S., M.S. and ph. D Derees in Department of Electric Enineerin from ChonBuk National University in 985 to 996. He was senior researcher in the LG Semiconductor Institute of Technoloy from 997 to 998. He is currently a professor at Department of IT Applied System Enineerin, ChonBuk National University since 999. His research interests include interated circuit desin of the analo and diital mixed mode sinal processin. Jun-Ho Ban He received the B.S. deree in Department of Electric Enineerin from Wonkwan University in 984. And M.S Deree in Department of Electric Enineerin from Konkuk University in 986, ph. D Deree from Wonkwan University in 993. He is currently a professor at Department of IT Applied System Enineerin, ChonBuk National University since 999. His research interests include FA system, Smart Grid and electric circuit system. Je-Ho Son He received the B.S. deree in Department of Electronic Enineerin from Wonkwan University in 99. And M.S. deree in Department of Electronic Enineerin from Wonkwan University in 995, Ph. D. deree from Wonkwan University in He is currently a professor at Department of IT Applied System Enineerin, ChonBuk National University since 996. His research interests include VLSI, Information Communication, Communication Network System, and DSP desin. Copyriht c 203 SERSC 49

12 Vol.6, No.6 (203) Hyun-Jun Chun He received B.S. deree in Department of Electronic Enineerin from Wonkwan University in 203. And He is currently a M.S. deree course of IT Applied System Enineerin from ChonBuk National University since 203. His research interests include Interated circuit desin of system semiconductor. 50 Copyriht c 203 SERSC