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U04504127132
U04504127132
U04504127132
U04504127132
U04504127132
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U04504127132

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International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of …

International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.

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  • 1. Jigyasa Singh et al Int. Journal of Engineering Research and Applications www.ijera.com ISSN : 2248-9622, Vol. 4, Issue 5( Version 4), May 2014, pp.127-132 www.ijera.com 127 | P a g e A High Speed CMOS Current Comparator at Low Input Current Jigyasa Singh, Sampath Kumar V. JSS Academy of Technical Education, Noida – 201301, India Abstract Analysis of high speed CMOS current comparator is presented with low input impedance using a simple biasing method. The simulation results from PSPICE demonstrate the propagation delay at low input currents at supply voltages of 1.8v, 2v, 2. 2v and stability analysis using 0.25um CMOS technology. So it is suitable to high speed applications. Keywords—Current comparators, propagation delay, positive feedback, signal processing. I. INTRODUCTION Current comparators are important building blocks within many analogue circuits designs. In particular, they are used for front-end signal processing applications and increasingly within neuromorphic electronic systems [1,2]. A/D converters may be designed using current-mode technologies. Since many digital and analog circuits have been tried to switch from voltage mode to current, mode operations. Current comparators may be the key elements. It consumes less power dissipation, achieves more dynamic range and high operation speed. Thus the current mode circuit design methodology receives increasingly wide attention in recent years [3,4]. In order to detect low current with high speed, many current comparators have been proposed. The simplest current comparator with positive feedback and low input impedance is shown in fig.1 [5] i.e. Traff current comparator. When the input current (Iin) flows into the circuit through V1, Vout is high. When input current (Iin) flows out of the circuit, Vout is low. CMOS inverters at the output stage to give rail-to-rail voltage swing. If the input current is small enough, there exists a deadband problem where the input impedance is quite high during input transition thus limiting the speed of operation. For reducing the deadband region of current comparator change its biasing scheme from class B to class AB. Another approach using resistor feedback to detect small currents shown in fig.2 [6].A simple current-source inverting amplifier seems attractive for many applications, but its large output resistance prevents its use at high speed, especially for capacitive loads. High speed current comparator requires low input impedance for increased current sourcing and sinking capability. Input and output resistance can be reduced by resistive feedback in first inverting amplifier in the input stage of current comparator. More inverters are required at the output stage to produce rail-to-rail output swing. This comparator is good for high speed at low input current but the power consumption is much higher due to constant current. RESEARCH ARTICLE OPEN ACCESS M1 M2 M3 M4 M5 M6 Vout Iin V1 V2 1 2 Fig.1
  • 2. Jigyasa Singh et al Int. Journal of Engineering Research and Applications www.ijera.com ISSN : 2248-9622, Vol. 4, Issue 5( Version 4), May 2014, pp.127-132 www.ijera.com 128 | P a g e Fig.2 II. 13TCURRENT COMPARATOR Since the response of original current comparators degrades drastically at low input current. One of the most significant problem of deadband has been minimized. Fig.3 shows the 13T current comparator which has one diode-connected enhance the speed. M8-M11 are the pairs of CMOS inverters to amplify the output signal. The two transistors Mp and Mn are used to adjust the inverter threshold voltage of M8 and M9 using different voltages values of Vn and Vp. For typical case Gate of Mp i.e. Vp is connected to ground and Mn i.e. Vn is connected to Vdd. Fig.3 transistor NMOS transistor instead of using two to provide voltage drop between the gates of M1 and M2. M3 and M5 forms the reference current generating stage. Input current (Iin) is connected to the first stage of the circuit. The drain and source of M4 is connected to the gates of M6 and M7. M4 is used to give higher current for charging and discharging the gates of M8 and M9 and thus III. PERFORMANCE ANALYSIS The 13T current comparator is simulated for various input currents and compared with circuits of fig.[1] and fig.[2] at Vdd=1.8v,2v,2.2v using 0.25um. Fig.4,5,6 shows the transient analysis of three different current comparators. In this propagation delay of current comparators is presented. The propagation delay is defined as the difference of time
  • 3. Jigyasa Singh et al Int. Journal of Engineering Research and Applications www.ijera.com ISSN : 2248-9622, Vol. 4, Issue 5( Version 4), May 2014, pp.127-132 www.ijera.com 129 | P a g e 300 320 340 360 380 400 420 180 200 220 240 Propagationdelay(ps) Input current(uA) Propagation delay vs Input current TRAFF CURRENT RESISTIVE FEEDBACK 13T CURRENT between the output and input when they reach the 50% of the total variation. The speed of 13T current comparator is much faster than other two comparators at 190uA and low power consumption is achieved at 1.8v. The resistor feedback is also good for high speed at low input current but the delay time is still longer than the 13T current comparator. Transient analysis of Traff current comparator Fig.4 Transient analysis of resistor feedback current comparator Fig.5 Transient analysis of 13T current comparator Fig.6 IV.COMPARISON TABLES TRANSIENT ANALYSIS FOR PROPAGATION DELAY TABLE 1: Comparison of current comparators at Vdd=1.8v Graph(a) of Table1 T i m e 0 s 1 0 n s 2 0 n s 3 0 n s 4 0 n s 5 0 n s 6 0 n s 7 0 n s 8 0 n s 9 0 n s 1 0 0 n s I ( I 1 ) 0 A 5 0 u A 1 0 0 u A 1 5 0 u A 2 0 0 u A Time 0s 10ns 20ns 30ns 40ns 50ns 60ns 70ns 80ns 90ns 100ns V(VOUT) 0V 0.5V 1.0V 1.5V 2.0V T i m e 0 s 1 0 n s 2 0 n s 3 0 n s 4 0 n s 5 0 n s 6 0 n s 7 0 n s 8 0 n s 9 0 n s 1 0 0 n s I ( I 1 ) 0 A 5 0 u A 1 0 0 u A 1 5 0 u A 2 0 0 u A T i m e 0 s 1 0 n s 2 0 n s 3 0 n s 4 0 n s 5 0 n s 6 0 n s 7 0 n s 8 0 n s 9 0 n s 1 0 0 n s V ( V O U T ) - 0 . 4 V 0 V 0 . 4 V 0 . 8 V 1 . 2 V 1 . 6 V 2 . 0 V Time 0s 10ns 20ns 30ns 40ns 50ns 60ns 70ns 80ns 90ns 100ns V(VOUT) -0.4V 0V 0.4V 0.8V 1.2V 1.6V 2.0V VDD= 1.8V TRAFF CURRENT COMPAR ATOR RESISTIVE FEEDBACK COMPARAT OR 13T CURREN T COMPAR ATOR Input current (uA) propagation delay(ps) propagation delay(ps) propagatio n delay(ps) 190 421.466 326.5655 310.1485 195 411.7385 347.636 330.4525 200 406.1915 354.861 340.8425 205 396.9805 356.813 354.816 210 395.381 359.0665 355.914 215 386.907 384.572 385.5225 220 382.747 405.591 401.9985 225 376.164 408.2525 410.286
  • 4. Jigyasa Singh et al Int. Journal of Engineering Research and Applications www.ijera.com ISSN : 2248-9622, Vol. 4, Issue 5( Version 4), May 2014, pp.127-132 www.ijera.com 130 | P a g e TABLE2: Comparison of current comparators at Vdd=2v Graph(b) of Table 2 TABLE 3: Comparison of current comparators at Vdd=2.2v VDD= 2.2V TRAFF CURRENT COMPAR ATOR RESISTIVE FEEDBAC K COMPARA TOR 13T CURREN T COMPAR ATOR Input current (uA) propagation delay(ps) propagation delay(ps) propagatio n delay(ps) 190 334.436 327.1645 322.1485 195 331.4125 331.27 324.4525 200 324.0825 345.232 335.8425 205 313.954 356.4445 336.816 210 306.5965 357.155 342.914 215 299.647 358.0365 348.5225 220 292.1155 359.98 355.9985 225 283.0775 359.28 360.286 Graph(c) of Table 3 V.AC ANALYSIS FOR STABILITY Phase margin and Gain margin of Traff current comparator Table 1a Traff current comparator Phase margin Gain margin(db) With stability 50.45590 12.73633 Without stability 42.68272 6.30394 230 260 290 320 350 380 410 440 470 500 0 5 10 propagationdelay(ps) input current(uA) Propagation delay vs input current TRAFF CURREN T RESISTIV E FEEDBAC K 13T CURREN T 250 270 290 310 330 350 370 390 410 0 5 10 Propagationdelay(ps) input current(uA) Propagation delay vs input current TRAFF CURRENT RESISTIV E FEEDBAC K 13T CURRENT VDD =2V TRAFF CURRENT COMPARA TOR RESISTIVE FEEDBACK COMPARA TOR 13T CURREN T COMPAR ATOR Input curren t (uA) Propagation delay(ps) Propagation delay(ps) propagatio n delay(ps) 190 458.669 257.236 250.1485 195 455.659 298.955 284.4525 200 453.05 318.6625 315.8425 205 450.877 322.6635 315.816 210 448.6555 325.5635 320.914 215 434.4925 326.429 322.5225 220 398.7235 328.499 329.9985 225 396.5835 329.2535 331.286
  • 5. Jigyasa Singh et al Int. Journal of Engineering Research and Applications www.ijera.com ISSN : 2248-9622, Vol. 4, Issue 5( Version 4), May 2014, pp.127-132 www.ijera.com 131 | P a g e Phase margin and gain margin of resistor feedback current comparator Table 1b With stability Iin-Iref (mA) Phase margin Gain margin(db) 2mA(50-48) 49.99984 10.34619 4mA(50-46) 52.54245 11.33189 6mA(50-44) 53.95440 11.32349 10mA(50-40) 55.48013 11.31445 Without stability Iin-Iref (mA) Phase margin Gain margin(db) 2mA(50-48) 49.99984 10.34619 4mA(50-46) 52.54245 11.33189 6mA(50-44) 53.95440 11.32349 10mA(50-40) 55.48013 11.31445 Phase margin and gain margin of 13T current comparator (Without stability) (With stability) Table 1c 13T current comparator Phase margin Gain margin(db) Without stability 30.14507 7.72318 With stability 48.55657 12.76250  POWER DISSIPATION Graph (d) Table 1,2,3 shows the propagation delay and its graph a,b,c. Table 1a, 1b, 1c shows the stability analysis of three different current comparators. Graph (d) represents the power dissipation with respect to Vdd. VI. CONCLUSION In this paper a high speed CMOS current comparator is presented using simple biasing method. In addition to less number of transistors the performance is better than both the comparators. From simulated results we concluded that 13T current comparator at 2v is much stable, delay time reduces with optimum power dissipation is achieved. REFERENCES [1] D.J. Banks, P.degenaar, and C.Toumazou, ―A colour and intensity contrast segmentation algorithm for current mode pixel distributed edge Detection,‖Eurosensors XIX, Barcelona,2005. [2] D.J. Banks, P.Degenaar, and C.Toumazou, ―Distributed Current-mode Image processing Filters,‖ Electronics letters, 41, pp.1201-1202, 2005. F r e q u e n c y 1 0 0 H z 1 . 0 K H z 1 0 K H z 1 0 0 K H z 1 . 0 M H z 1 0 M H z 1 0 0 M H z 1 . 0 G H z 1 0 G H z 1 0 0 G H z D B ( V ( O U T ) ) - 1 5 0 - 1 0 0 - 5 0 - 0 5 0 Frequency 100Hz 1.0KHz 10KHz 100KHz 1.0MHz 10MHz 100MHz 1.0GHz 10GHz 100GHz P(V(OUT)) -600d -500d -400d -300d -200d -100d -0d Frequency 100Hz 1.0KHz 10KHz 100KHz 1.0MHz 10MHz 100MHz 1.0GHz 10GHz 100GHz DB(V(OUT)) -150 -100 -50 -0 50 Frequency 100Hz 1.0KHz 10KHz 100KHz 1.0MHz 10MHz 100MHz 1.0GHz 10GHz 100GHz P(V(OUT)) -600d -500d -400d -300d -200d -100d -0d 0 0.5 1 1.5 2 2.5 3 1.8 2 2.2 Powerdissipation(mW) Vdd(v) Power dissipation with respect to Vdd Traff current Resistive feedback 13T current
  • 6. Jigyasa Singh et al Int. Journal of Engineering Research and Applications www.ijera.com ISSN : 2248-9622, Vol. 4, Issue 5( Version 4), May 2014, pp.127-132 www.ijera.com 132 | P a g e [3] H.Hassan, M. Anis, and M. Elmasry, ―MOS current mode circuits: Analysis, Design, and variability,‖ IEEE Transactions on VLSI, Vol. 13, no.8, pp. 885-898, Aug.2005. [4] G.K. Balachandran and P.E. Allen, ―Switched current circuits in digital CMOS technology with low charge-Injection Errors,‖IEEE journal of solid-state circuits,Vol. 37, no. 10 pp. 1271-1281, oct.2002. [5] H.Traff, ―Novel approach to high speed CMOS current comparators,‖ Electron. Lett. Vol.28, no. 3, pp. 310-312, 1992. [6] B.-M. Min and S.-W. Kim, ―High performance CMOS current comparator using resistive feedback network,‖ Electron lett. vol. 34, no.22, pp.2074-2076, 1998. [7] A.Tang and C.Toumazou, ―High performance CMOS current comparators,‖ Electronicslett.,vol.33,no.22,pp.1829-1830, 1997. [8] L.Ravezzi, D.Stoppa and G.-F Dalla Betta, ―Simple high speed CMOS current comparators,‖Electronicslett.vol.33,no.22,pp .1829-1830, 1997.

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