INTERNATIONAL JOURNAL OF ADVANCES IN COMPUTING AND INFORMATION TECHNOLOGY An international, online, open access, peer reviewed journal Volume 2 Issue 2 April 2013 Research Article ISSN 2277–9140 © Copyright by the authors - Licensee IJACIT- Under Creative Commons license 3.0
Voltage feedback v/s Current feedback operational amplifier using BJT and CMOS Arpit Kuthiala, Ankur Agarwal, Abhimanyu Gupta, Shruti Jain Department of Electronics and Communication Engineering Jaypee University of Information Technology, Solan-173215, India
[email protected] doi:10.6088/ijacit.22.10002 ABSTRACT In this process of Complementary metal oxide semiconductor (CMOS) technology development, the supply voltage has been decreasing while the transistor threshold voltages do not effectively scale and the inherent gain available from the transistors has been decreasing with downsizing of the transistor gate length. The paper focuses on the Common-Mode Rejection Ratio (CMRR), Slew Rate, Power dissipation and Power supply on the internal circuitry of the voltage feedback op-amp and current feedback op-amp using BJT and CMOS for the three configurations. For the simulation of circuits we have used PSPICE software. We come to know that the CMRR ratio and the power dissipation for CMOS Op-Amp are much less as compared to BJT Op-Amp. The power supply required for BJT Op-Amp is approximately thrice the supply power required for CMOS Op-Amp. Also for Current feedback Non inverting configuration is best while for voltage feedback, inverting configuration is best because the value of CMRR ratio is the highest. Keywords: Operational Amplifier (op-amp), voltage feedback, current feedback, CMRR 1. Introduction Linear integrated circuits are being used in a number of electronic applications such as in fields like audio and radio communication, medical electronics, instrumentation control etc. As long as the inputs and output stays in the operational range of the amplifier, it will keep the differential input voltage at zero, and the output will be the input voltage multiplied by the gain determined by the feedback network. Operational amplifiers are among the most widely used building blocks in electronic circuits. An ideal operational amplifier would have infinite voltage gain, infinite input resistance, zero output resistance and infinite CMRR. Using feedback, the bandwidth can be increased by trading gain against bandwidth. When a portion of the output is fed back to the inverting terminal of the input to establish a fixed gain, it is termed as negative feedback. Using negative feedback, the gain can be reduced and op-amp can be stabilized. For an open loop op-amp, the gain is infinite and by applying only a small voltage at the input, the output saturates in the direction of supply voltages (Vcc or Vss). The voltage difference at the input of the op-amp is multiplied by the gain open loop gain of the op-amp which is infinite for ideal op-amp. If higher voltage is applied at the inverting terminal (-) than the non-inverting terminal (+) of the op-amp, the output will swing negative. If
Received on March 2013, Published on April 2013
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Voltage feedback v/s Current feedback operational amplifier using BJT and CMOS
higher voltage is applied at the non- inverting terminal (+) than the inverting terminal (-) of the op-amp, the output will swing positive. Thus, the infinite gain of open-loop amplifier will force the differential voltage to be zero.
There are basically four types of feedback :
Voltage series feedback (Voltage feedback) Voltage shunt feedback Current series feedback Current shunt feedback (Current Feedback)
2. Voltage feedback amplifiers A closed loop configuration in which the error signal or differential signal is voltage is called voltage feedback amplifier.
Figure 1 Basic Voltage Feedback Here, Vd = differential voltage aVd = output voltage For the voltage feedback circuit shown above, on applying the negative feedback, the op-amp drives the differential voltage to zero and hence named as voltage feedback. The transfer function of the circuit is given by the ratio of output voltage (Vo) to the input voltage (Vi). The four stages of an op-amp are:
Dual Input Balanced Output. Dual Input Unbalanced Output. Emitter Follower / Level Shifter. Push-Pull Amplifier.
3. Current-feedback amplifiers These circuits work only for high-frequency applications. In this case, the error signal is the current and is much faster than voltage feedback.
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Voltage feedback v/s Current feedback operational amplifier using BJT and CMOS
Figure 2: Basic Current Feedback Here the unity gain is connected to the non-inverting input and acts as an emitter follower circuit. The noninverting input act as an input of the buffer and thus has a very high impedance G B. Since the output of buffer is connected to the inverting terminal, the input impedance for the inverting terminal is low in case of CFA, ZB. The voltage generated by the inverting terminal is given as Vin = Z x I The output voltage source Z(I) becomes the output voltage after modeling through GOUT and ZOUT . The output of a current-feedback op amp is a voltage and is related to the current that flows out of or into the inverting input of the op amp by a complex function called trans-impedance, Z(s). The value of Z(s) is very high for DC. The main advantage of current feedback op-amp is adjustable bandwidth and stability. The ideal CFA can be configured in two basic ways :
Non-inverting Inverting
3.1 The Non-inverting Current Feedback Amp (CFA) : The output is in phase with the input. The gain for the non-inverting configuration is given as
G 1
ZF ZG
Here, ZF = Feedback Resistance ZG = Input Resistance
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Voltage feedback v/s Current feedback operational amplifier using BJT and CMOS
Figure 3 Non-Inverting current feedback Op-Amp Vout = I.Z 3.2 The Inverting Current Feedback Amp (CFA) The output is out of phase with the input. The gain for the inverting configuration is given as
G ZF
ZG
Figure 4 Inverting current feedback Op-Amp Here, ZF = Feedback Resistance ZG = Input Resistance 4. Results and Discussions The differential amplifier input structure is not available in current feedback amplifiers and hence the parameter matching is not possible to this structure.
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Voltage feedback v/s Current feedback operational amplifier using BJT and CMOS
However, the CFA has higher bandwidth and Slew Rate in comparison to VFA. Since the higher bandwidth is not dependent on closed-loop gain, thus the constrain of having a constant gain-bandwidth product in VFA is removed for CFA. The slew rate for CFA is better as compared to VFA because the output is enabled to supply slewing current until the output attains its final value. However VFA are applicable for general and precision purposes whereas CFA’s work only for frequency greater than 100MHz. CFA find use in video application because of their ability to be DC-coupled in video applications as dynamic range is not very important there. CFA’s are mostly Dc-coupled while they operate in the GHz range. The slew rate for CFA is faster as compared to VFA and hence faster rise and fall times. 4.1 Voltage feedback operational amplifier Figure5 shows the circuit diagram for voltage feedback operational amplifier using BJT and Figure6 shows diagram using CMOS
Figure 5: Voltage feedback operational amplifier using BJT
Arpit Kuthiala et al International Journal of Advances in Computing and Information Technology
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Voltage feedback v/s Current feedback operational amplifier using BJT and CMOS 0
V1 5V
Q1 ZVN4206/TO Q2 ZVN4206/TO Q4 ZVN4206/TO
Q6 ZVN4206/TO V4
Q5 ZVN4206/TO
Q7 ZVN4206/TO V3 R1 2K
I1 DC = 100UA Q3 ZVN4206/TO
C1
0
1PF Q8 ZVP2110/TO
Q10 ZVP2110/TO
Q9 ZVP2110/TO
V2 5V
0
Figure 6: Voltage feedback operational amplifier using CMOS As we know that there are three different configurations for each operational amplifier i.e. inverting configuration, Non-inverting configuration and Differential configuration. We have performed the three operations on Fig 5 and Fig 6 using PSPICE software and get different parameters shown in table 1 Table 1: Comparison table for Voltage feedback operational amplifier using BJT and CMOS
4.2 Current feedback operational amplifier Figure7 shows the circuit diagram for current feedback operational amplifier using BJT and Figure8 shows diagram using CMOS
Arpit Kuthiala et al International Journal of Advances in Computing and Information Technology
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Voltage feedback v/s Current feedback operational amplifier using BJT and CMOS
V1 15V
Q16 Q2N4403
Q14 Q2N4403
Q19
Q21
Q23 Q2N4403
Q2N4403
Q2N4403 Q13 Q7
Q18 Q2N2222
R1 1k
Q15
Q2N2222 V1 = 0V V2 = 5V
Q1
Q2N4403
Q2N2222
R3 100 V1 = 0V V2 = 5V
Q2N4403 V4
R4 100
Q17
1n
Q2N4403
V3
Q12
C1
Q20
Q2N2222
Q11
Q2N4403 Q22
Q2N2222
Q3 Q2N2222
Q2N4403
Q6
Q2N2222 Q8 Q2N2222
Q9
Q10
Q2N2222
Q2N2222
V2 15V
Figure 7: Current feedback operational amplifier using BJT
V1 5VDC
Q1 ZVN4310A/TO
Q2 ZVN4310A/TO
Q3 ZVN4310A/TO
Q7 ZVP0545/TO I1
I3
100UA
Q5 ZVP0545/TO I2
Q4 ZVP0545/TO Q6 ZVP0545/TO
V2 5VDC
Figure 8: Current feedback operational amplifier using CMOS We have performed the three operations on figure 7 and Figure8 using PSPICE software and get different parameters shown in Table 2: Arpit Kuthiala et al International Journal of Advances in Computing and Information Technology
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Voltage feedback v/s Current feedback operational amplifier using BJT and CMOS
Table 2: Comparison table for Current feedback operational amplifier using BJT and CMOS
5. Conclusion The circuits for Op-Amp using BJT and CMOS for voltage feedback and current feedback in the three configurations, the performance of the two have been compared for various parameters. The CMRR ratio and the power dissipation for CMOS Op-Amp is much less as compared to BJT Op-Amp. In case of Voltage feedback Op-Amp using BJT, The inverting Configuration is the most efficient because the value of CMRR ratio is the highest and highest value tend to ideal behavior of the Op-Amp. In case of Voltage feedback Op-Amp using CMOS, The inverting Configuration is the most efficient because the value of CMRR ratio is the highest. In case of Current feedback Op-Amp using BJT and CMOS, The non-inverting Configuration is the most efficient because the value of CMRR ratio is the highest. The supply power required for BJT Op-Amp is thrice the supply power required for CMOS Op-Amp. 6. References 1. D. Roy Choudhury and Shail B. Jain, (2003), Linear Integrated Circuits 2nd Ed. New Age International. 2. Gayakwad R, (2000),OP-Amplifier and Linear Integrated Circuits. 4th edition, Prentice Hall. 3. E. Bruun, (1992), A dual current feedback CMOS op amp. PTOC. Tenth NORCHIP Seminar, pp. A9A11, Helsinki 4. E. Bruun. (1993),CMOS Technology and Current Feedback Op-Amp. IEEE, pp 1062-1065 5. Madian, A. H., Mahmoud, S. A., Soliman, A.H. (2007), Low voltage CMOS fully differential current feedback amplifier with controllable 3-dB bandwidth IEEE International Conference on Signal Processing and communications. 6. Raikos, G. and Psychalinos, C. (2009), Low Voltage current feedback operational amplifier. Circuits Syst Signal Process, pp 377-388. 7. Pennisi, (2005), High-performance CMOS current feedback operational amplifier, in Proc. IEEE Int. Symp. on Circ. and Syst. (ISCAS), II, Kobe, Japan, pp. 1573–1576 8. Heydari, P., Mohavavelu, R., (May 2003), Design of Ultra High-Speed CMOS CML buffers and Latches. Proceedings of the 200th InternationalSymposium on Circuits and Systems, Volume 2. 9. Current-Feedback Op Amp Analysis. Literature Number SLOA080, Chapter 8, Texas instruments.
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