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研究生:Gene Fe Panes Palencia
研究生(外文):Gene Fe Panes Palencia
論文名稱:切換電容式三角調變之展頻時脈產生器
論文名稱(外文):Triangular Modulation using Switched-Capacitor Scheme for Spread Spectrum Clocking
指導教授:黃弘一
指導教授(外文):Huang, Hong-Yi
口試委員:蘇朝琴江正雄
口試委員(外文):Su, Chau-ChinChiang, Jen-Shiun
口試日期:July 21, 2011
學位類別:碩士
校院名稱:國立臺北大學
系所名稱:電機工程研究所
學門:工程學門
學類:電資工程學類
論文種類:學術論文
論文出版年:2011
畢業學年度:99
語文別:英文
論文頁數:111
中文關鍵詞:切換式電容、展頻時脈產生器、三角調變器、諧波、減小EMI
外文關鍵詞:switched-capacitor, SSCG, triangular modulation profile, harmonics, EMI reduction
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本論文之三角調變器使用交換式電容方式來實現展頻時脈產生器,工作原理為輸入訊號調變為三角波訊號,將分散各次諧波的能量呈一定頻率的波段,因而降低峰值電磁干擾(EMI)的諧波頻率。本研究之三角調變器總電容為20pF,在Hspice模擬中使用1um高電壓製程來實現。調變信號頻率為257赫茲和幅度為150 mVpp主要應用於65 kHz振盪器。頻率誤差是大約在±4千赫茲左右。模擬結果顯示EMI減少13.8分貝。此電路是應用於振盪電路中的PWM控制器IC。電力損耗為2.16mW。傳統的理論分析和創新的部份也是使用公式證明。人工計算指數與模擬部分相比最大誤差為3.1%。
A triangular modulation profile using switched-capacitor scheme for spread spectrum clock generator (SSCG) is presented in this paper. The working principle consists of modulating the oscillator’s constant clock frequency with a triangular signal. This will spread the energy of each harmonics into a certain frequency band, thus reducing the peak amplitude of electromagnetic interference (EMI) at harmonic frequencies. This work aims to implement triangular modulation with a constraint of 20pF total capacitor for cost efficiency. The device models of a 1um high-voltage CMOS process is applied for Hspice simulation. The modulating signal which has a frequency of 257 Hz and amplitude of 150 mVpp is used to modulate a 65 kHz oscillator. The frequency deviation is maintained to be within ± 4 kHz. Simulation shows an EMI reduction of 13.8 dB. This work is applied in the oscillator circuit of a PWM controller IC. The power consumption is 2.16mW. Theoretical analysis of traditional modulations and the proposed scheme are also formulized. The hand calculation of the modulation index using the proposed formula has only a maximum error of 3.1 percent compared to simulation.
Acknowledgement ……… I
Abstract ………………………… IV
Table of Contents ………… VI
List of Figures ……………… IX
List of Tables ………… XII


Chapter 1:
Introduction ………………………………1
1.1 Background …………………1
1.2 Motivation ………………… 2
1.3 Thesis Organization ……… 3

Chapter 2: Fundamentals of Frequency Modulation…… 4
2.1 Introduction ……………… 4
2.2 Frequency Modulation …………………………… 6
2.2.1 Modulation Index, mf…………………… 9
2.2.2 Modulation Ratio, δ ……………………… 10
2.2.3 Bandwidth Consideration …………………… 11
2.3 Modulation Profiles ………………………………………… 12
2.4 Spread Spectrum Technique for EMI Reduction ……………17
2.4.1 Jitter Frequency Modulation ………………………. 18
2.4.2 Principle of Jitter Frequency Modulation …………19
2.4.2.1 Current-Controlled Switches ………………... 23
2.4.2.2 4-bit Switched-Capacitor …………………………26

Chapter 3: Spread Spectrum Clock Generator for EMI Reduction ………………………………………………..... 32
3.1 Introduction …………………………………………………32
3.2 Triangular Waveform Generator ………….………………… 34
3.2.1 Switched-Capacitor …………………………………….. 36
3.2.1.1 MOSFET as a Switch …..……………………. 36
3.2.1.2 Charge Injection ………….……………….… 37
3.2.1.3 Clock Feedthrough …………………………...... 39
3.2.1.4 Switched-Capacitor Circuit ……..………………. 40
3.3 Non-overlapping Clock Generator ……………………… 46
3.4 Two-stage Operational Amplifier …………………………... 50
3.4.1 Comparator ………………………………………... 51
3.4.2 Unity-gain Buffer Amplifier ………………………. 52
3.5 Voltage Reference ………………………………………….. 52
3.5.1 Bandgap Reference Circuit ……………………………. 52
3.5.2 LDO-type Voltage Reference …………………………... 54
3.6 Constant-gm Current Reference ……………………………. 55
3.7 Oscillator Circuit …………………………………………… 57

Chapter 4: Simulation Results and Comparison ………..…………. 66
4.1 Simulation of Voltage Reference …………………………… 66
4.2 Function Simulations of the Proposed Triangular Waveform Generator .…………………………………………………… 68
4.2.1 Non-overlapping Clock Circuit ……………………. 68
4.1.2 Modulating Signal Vm and fm and fmb ………………. 70
4.3 Spread Spectrum of the Oscillator with the Proposed
Triangular Modulation ……………………………………...... 72
4.4 Function Simulations of the 4-bit Current-controlled
Switch Technique …………………………………………….. 75
4.4.1 Frequency Divider …………..…………………….. 75
4.4.2 4-bit Current-controlled Switch …..……………….. 77
4.5 Spread Spectrum with 4-bit Current-controlled Switch ……. 80
4.6 Function Simulations with 4-bit Switched-Capacitor Technique ................................................................................ 81
4.7 Spread Spectrum with 4-bit Switched-Capacitor Technique …………………………………………................ 84
4.8 Comparison ………………………………………….……... 85

Chapter 5: Conclusion and Future Work ……..……………………. 90
5.1 Conclusion ………………………………………………….. 90
5.2 Future Work ………………………………………………… 91

References ……………...………………………………………………92






LIST OF FIGURES

Figure 2.1 Block diagram of a modulator ………………………………. 5
Figure 2.2 Sinusoidal frequency modulation’s effect (a) modulating
wave; (b) instantaneous frequency of FM waveform;
(c) instantaneous angle of FM waveform … …………………… 7
Figure 2.3 Frequency Spectrum ………………………………………… 9
Figure 2.4 Spread spectrum showing (a) down-spreading,
(b) symmetrical and (c) up-spreading SSCG techniques ..…... 12
Figure 2.5 Sinusoidal, triangular and exponential modulation
profiles ……………………………………………………...... 14
Figure 2.6 Spectral Analysis (a) increasing mf with fm held fixed (b) effect of increasing mf by decreasing fm with ∆fc held fixed. …16
Figure 2.7 Spread spectrum bands of the harmonics in modulated
square signals ……………………………………………....... 17
Figure 2.8 Oscillator circuit diagram with 4-bit current-
controlled switch ……………………………………………... 23
Figure 2.9 Oscillator’s circuit diagram with 4-bits switch capacitor …..27
Figure 3.1 Block diagram of the proposed triangular waveform
generator with the main oscillator ……………...……………. 35
Figure 3.2 Sample and hold circuit (a) with NMOS device
(b) charge injection …….…………………………………...... 36
Figure 3.3 Clock feedthrough in a sampling circuit ……….………….. 39
Figure 3.4 Switched-capacitor circuit……….………………………... 40
Figure 3.5 The switched-capacitor circuit used to produce Vm ……… 41
Figure 3.6 Circuit operation of the proposed triangular signal generator ……………………………….…….…..…………... 42
Figure 3.7 Key waveforms in generating the triangular signal ……….. 43
Figure 3.8 Complete circuit diagram of the proposed triangular signal generator ………………………………………………........... 45
Figure 3.9 Clock waveforms …………..……………………….……... 47
Figure 3.10 Non-overlapping clock generator ………………..………. 48
Figure 3.11 Non-overlapping clock signals …………..………………. 49
Figure 3.12 Non-overlapping clock generator with symmetrical
output signals ………………………………………………… 50
Figure 3.13 Two-stage operational amplifier circuit diagram ……..….. 51
Figure 3.14 Bandgap reference …………………………………….….. 53
Figure 3.15 LDO-type voltage reference circuit diagram ………….…. 54
Figure 3.16 Constant-gm current reference circuit …………………..... 55
Figure 3.17 Oscillator block diagram …………………………………. 58
Figure 3.18 Oscillator circuit ………………………………………….. 60
Figure 3.19 Ideal transient waveform …………………………………. 62
Figure 4.1 Voltage reference ………………………………………… 67
Figure 4.2 Simulation results of non-overlapping clock generator ........ 69
Figure 4.3 Vm and fm and fmb signals .…………………………………. 71
Figure 4.4 Spread Spectrum with the proposed triangular modulation…72
Figure 4.5 Comparison of the spread spectrum for with and without modulation …………………………………………………… 74
Figure 4.6 Frequency divider using DFF .…………………………...... 75
Figure 4.7 Control bits ………………………………………………… 76
Figure 4.8 DFF using transmission gate ………………………………. 77
Figure 4.9 Oscillator circuit diagram with 4-bit current controlled
switch technique for EMI reduction………………………….. 78
Figure 4.10 Simulation results with 4-bit switched current-controlled technique …..…………………………………………………… 79
Figure 4.11 Spread spectrum of the oscillator with 4-bit
current-control technique……………………………………...... 80
Figure 4.12 Simulation results with 4-bit switched-capacitor ………… 83
Figure 4.13 Spread spectrum with 4-bits switched-capacitor …………..84
Figure 4.14 Comparison of spread spectrum ………………………… 86
















LIST OF TABLES

Table 2.1 Spectrum of the three types of modulation method ………… 15
Table 2.2 System Requirements ………………………………………. 31
Table 4.1 Bandgap reference sensitivity ………………………………. 67
Table 4.2 Voltage reference temperature sensitivity ……………………68
Table 4.3 Characteristic table of modulating signal, fm ….……………. 71
Table 4.4 Performance table summary of the oscillator with triangular modulation ……………………………………………………… 73
Table 4.5 Corner simulation of the proposed circuit….………………...74
Table 4.6 Control bit clock frequencies ……………………………….76
Table 4.7 Oscillator circuit performance table with current-controlled technique ………………………………………………………...81
Table 4.8 Circuits’ performance table with 4-bit switched-capacitor ….85
Table 4.9 Performance comparison of the three techniques……….87
Table 4.10 Theoretical comparison of the three techniques ……………88
Table 4.11 Comparison with previous work ………………………….88

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