CMOS Optical Preamplifier Design Using Graphical Circuit Analysis

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2.4 Circuit Analysis Techniques 24 the device and circuit level will be required to ensure the long-term feasibility of low-voltage optical receivers. In this thesis, we present a 1V optical receiver front- end implemented in a standard CMOS process without low-threshold devices. The design incorporates both a novel transimpedance amplifier and a novel voltage doubler capable of accepting input levels below 1V. The feedback resistor is implemented using a MOSFET operating in the linear region, and the gate of the MOSFET is biased by the voltage doubler. While the interest in low-voltage optical receivers has emerged quite recently, much work has already been done to develop low-voltage analog circuits. Innova- tions such as the switched-opamp [Steyaert,1993] and the nested-Miller compensa- tion technique [You,1997] are good examples. One observation that applies to many low-voltage circuits is that they differ significantly from their traditional counter- parts, and as such must be reanalyzed. Such was our experience with the low-voltage transimpedance amplifier, and it called upon us to further investigate alternative methods of circuit analysis which is the subject of the next section. 2.4 CIRCUIT ANALYSIS TECHNIQUES Nodal and mesh analysis are the two traditional forms of linear circuit analysis. Each involves deriving a set of linear equations using Kirchhoff’s Current (KCL) and Voltage (KVL) Laws [Bobrow,1987]. Other circuit analysis techniques specifi- cally suited for analyzing feedback structures include topology-based feedback analysis and feedback analysis based upon return ratios. Topology-based feedback analysis, as exemplified by [Sedra,1998], is per- formed by partitioning a feedback circuit into a forward amplifier and a feedback network as shown in Figure 2.11. This method requires us to identify the method used to sample the output and the method used to mix the feedback signal back to the input.
Source Figure 2.11 General structure of the feedback amplifier. 2.4 Circuit Analysis Techniques 25 The alternative method of analyzing feedback circuits requires determining the return ratio of a dependent source in an active device found in the feedback circuit. The return ratio is then used to calculate quantities such as gain, and input and output impedance [Rosenstark,1986]. Originally outlined by Bode [Bode,1945], its main advantage over topology-based analysis is that it neither requires the partitioning of the amplifier into two distinct components nor requires the identification of the sampling and mixing mechanisms. If we consider the model of the feedback amplifier shown in Figure 2.12 in which the controlled source represents, for instance, the transconductance of a transistor that is part of the internal feedback, the return ratio, T, can be defined by the following passage: “The return ratio,T,with reference to controlled source x b is defined as the negative of the variable x a which is produced when the dependent source x b is replaced by an independent source of the same nature and polarity but of strength k,all independent sources are set to zero and all other conditions in the system are left unchanged from their normal operating conditions.” 2 x 1 2. [Rosenstark,1986], p. 12. Σ Rest of feedback amplifier Controlled source + xa - Forward Amplifier A Feedback Network β xb= kxa Figure 2.12 Feedback amplifier model [Rosenstark,1986]. + x2 - x b Load
Page 1 and 2: CMOS Optical Preamplifier Design Us
Page 3 and 4: To achieve low-voltage operation, w
Page 5 and 6: Table of Contents CHAPTER 1 INTRODU
Page 7 and 8: CHAPTER 1 1.1 OVERVIEW Introduction
Page 9 and 10: Information Source Modulator Drive
Page 11 and 12: 1.2 Thesis Outline 5 [Ohhata,1999].
Page 13 and 14: 1.2 Thesis Outline 7 technique call
Page 15 and 16: 1.2 Thesis Outline 9 Detector in St
Page 17 and 18: E e + - V bias 2.1 Photodetectors 1
Page 19 and 20: Diode Capacitance (pF) Diode capaci
Page 21 and 22: 2.2 Optical Preamplifier Structures
Page 23 and 24: 2.3 Transimpedance Amplifier Design
Page 25 and 26: 2.3 Transimpedance Amplifier Design
Page 27 and 28: I dc 2.3 Transimpedance Amplifier D
Page 29: 2.3 Transimpedance Amplifier Design
Page 33 and 34: A = = For = 1V , the solution is v
Page 35 and 36: The gain of the forward amplifier c
Page 37 and 38: Feedback Analysis Using Return Rati
Page 39 and 40: 2.4 Circuit Analysis Techniques 33
Page 41 and 42: 2.5 An Overview of Signal-Flow Grap
Page 43 and 44: 1 x1 x2 2.5 An Overview of Signal-F
Page 45 and 46: 2.6 SUMMARY REFERENCES • ∆ k =
Page 47 and 48: Symp. Circuits Systems, vol. 3, pp.
Page 49 and 50: CHAPTER 3 New Transimpedance Amplif
Page 51 and 52: 3.1 A Differential Transimpedance A
Page 57 and 58: 3.2 A Feedback Topology for Ambient
Page 59 and 60: 3.2 A Feedback Topology for Ambient
Page 61 and 62: Transimpedance (dBΩ) 90 80 60 40
Page 63 and 64: 3.3 A Low-Voltage Transimpedance Am
Page 73 and 74: C 3 Φ1VB M 3 V B- =0.7V M 7 Figure
Page 77 and 78: 3.4 SUMMARY 3.4 Summary 71 In this
Page 79 and 80: 3.4 Summary 73 Y. Nakagome et al.,
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4.1 Introduction 75 back topology o
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4.2 Circuit Analysis Using Driving-
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4.3 DPI/SFG: Combining DPI Analysis
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4.4 Determining Port Impedances 87
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v i R in v o R out 4.4 Determining
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id » ro and 1 ⁄ rid « Av ⁄ ro
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Z b r e g m 4.5 Analyzing Transisto
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4.5 Analyzing Transistor Circuits 9
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Figure 4.25 SFG for the source foll
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5.1 Analysis of the Low-Voltage Tra
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5.1 Analysis of the Low-Voltage Tra
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5.2 DEVELOPING AN ANALYTIC CIRCUIT
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Z in 5.2 Developing an Analytic Cir
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5.2 Developing an Analytic Circuit
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I n1 : i in I n2 -I n1 i scin ( sCi
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I nRf : 5.2 Developing an Analytic
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DC transimpedance gain: Pole locati
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Frequency (MHz) 500 450 400 350 300
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Pole frequencies(MHz) 500 450 400 3
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Optimizing Sensitivity 5.2 Developi
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Transimpedance Volts dB (lin) Gain
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CHAPTER 6 Implementation and Experi
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6.1 A 1V Optical Receiver Front-End
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6.1.2 Experimental Results 6.1 A 1V
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Gain(dB) 0 −1 −2 −3 −4 −5
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Clock signal of voltage doubler Eye
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6.2 Variable-Gain Transimpedance Am
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6.2.2 Experimental Results 6.2 Vari
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6.3 Summary and State-of-the-Art Co
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Reference Outputs Technology Supply
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CHAPTER 7 Conclusions 7.1 SUMMARY A
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7.2 Future Work 165 The significanc
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7.2 Future Work 167 supply and subs
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v s i ti that part of the SFG for Q
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Thus, P1 ′ = b = 500Ω ∆1 ′
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itive representation of circuit dyn
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Bipolar Transistor i scb Z b v b b
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