CMOS Optical Preamplifier Design Using Graphical Circuit Analysis

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2.1 Photodetectors 12 There is a linear relationship between the photocurrent, is , and the irradiance, Ee , which is a measure of the intensity of the incident light and is given in W m . 2 ⁄ The photocurrent is calculated by where η is the quantum efficiency of device (typically in the range of 0.6 to 0.9), q is a unit electron charge ( 1.69 10 C), is Planck’s constant ( J/s), 19 – × h 6.626 10 34 – × υ is the frequency of the light, and Aeff is the effective area of the photodiode and accounts for the effect of the lens. The collective term, R = ηq ⁄ hυ, is commonly known as the responsivity of the device, and is in units of A/W. The product, ∅e = Aeff Ee , is the received optical power in Watts. For example, the Temic BPV22NF is rated to provide 85nA of photocurrent per 1 µW cm irradiance at 2 ⁄ 870 nm. The current source, , models the shot noise generated by the dc current which includes the photodiode’s intrinsic dark-current as well as photocurrent due to background light. The noise has a white spectrum with a normalized noise power density given by where is the dc component of . I s i s 2 I n ηq = ------ Aeff Ee = hυ R∅ e 2 I n( f ) = 2qIs A 2 ⁄ Hz i s (2.1) The remaining two elements of the model, and , represent the series resistance of the diode and the diode capacitance. Since the photodiode is operating under reverse-bias conditions, the capacitance is dominated by the depletion capacitance across the p-n junction. As a result, is greatly dependent on the applied bias voltage, as illustrated in Figure 2.3 for the BPV22NF photodiode. This characteristic is particularly significant when designing low-voltage receivers where the maximum reverse bias that can be applied to the photodiode is severely limited. R s Cd Cd C d
Diode Capacitance (pF) Diode capacitance (pF) 2.2 OPTICAL PREAMPLIFIER STRUCTURES 2.2 Optical Preamplifier Structures 13 0 0 2 4 6 8 10 12 14 16 18 20 0 2 4 6 8 10 12 14 16 18 20 Applied reverse bias voltage (Volts) Figure 2.3 Photodiode capacitance vs. bias voltage for the Temic BPV22NF. The optical preamplifier performs the critical function of interfacing the photodiode to the rest of the receiver. Typically, the preamplifier converts the received photocurrent into a voltage signal. The preamplifier plays a crucial role in determining many aspects of the overall performance of the receiver including speed, sensitivity, and dynamic range. Optical preamplifiers are typically based on a either a termination resistor or a transimpedance amplifier. In the first approach, the photodiode is attached to a load resistor, , as shown in Figure 2.4. The current signal, , is converted into a volt- R L 80 70 60 50 40 30 20 10 age by the load resistor, and the resulting voltage signal is buffered by the voltage amplifier. The capacitance represents the total capacitance associated with the C T photodiode and the amplifier. Reverse bias voltage (V) The choice of the load resistance affects both the frequency response and the noise performance of the preamplifier. The intrinsic bandwidth of the preamplifier is equal to 1⁄ ( 2πRLCT) because of the RCnetwork. The noise can be analyzed using i s
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: E e + - V bias 2.1 Photodetectors 1
Page 21 and 22: 2.2 Optical Preamplifier Structures
Page 23 and 24: 2.3 Transimpedance Amplifier Design
Page 27 and 28: I dc 2.3 Transimpedance Amplifier D
Page 31 and 32: Source Figure 2.11 General structur
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
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3.3 A Low-Voltage Transimpedance Am
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C 3 Φ1VB M 3 V B- =0.7V M 7 Figure
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3.4 SUMMARY 3.4 Summary 71 In this
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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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CMOS Optical Preamplifier Design Using Graphical Circuit Analysis

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