PCIRF_6_7_VCO
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Prof. C. Patrick Yue Slide 1 VCO Design Overview q Tunin g Range – need to cover all frequen cy channels q Noi se – negative i mpact on system p erformance — Receiver – lower sensiti vity, poorer blo cking perfor mance — Transmitter – increas ed spectral emissi ons (output spect rum must meet a mask requirement) q Power – want low po wer dissip ation q Isolation – want to minimiz e noise pathways into V CO q Sensitiv ity to PVT variations – need to make it man ufactur able in high volume
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Transcript of PCIRF_6_7_VCO
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Prof. C. Patrick Yue Slide 1
VCO Design Overview
q Tuning Range – need to cover all frequency channels
q Noise – negative impact on system performance
— Receiver – lower sensitivity, poorer blocking performance
— Transmitter – increased spectral emissions (output spectrum must meet a mask requirement)
q Power – want low power dissipation
q Isolation – want to minimize noise pathways into VCO
q Sensitivity to PVT variations – need to make it manufacturable in high volume
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Prof. C. Patrick Yue Slide 2
VCOs in Wireless Systems
q RF integrated systems typically employ a combination of simple mixing
with some image filtering and image reject mixing
q Using one or more IF stages to relax the filter requirements, but need todeal with images
q Using image reject mixers with I&Q LO signals to eliminate the need of
band-pass filters (to enable higher level of integration)
q VCO noise is characterized in frequency domain as phase noise
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Prof. C. Patrick Yue Slide 3
Transceiver Case Studies – Philips GSM Transceiver
q Dual conversion in both receive and transmit paths
q Two LNAs are used to allow the use of two low-cost lossy image-reject filters
q LO1 and LO2 are at 1.3 GHz and 400 MHz, respectively
q 30 dB of image reject for the 1.7 GHz interferer
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Prof. C. Patrick Yue Slide 4
VCOs for High-Speed Wireline Systems
q VCO noise also has a negative impact on wireline data links
— Receiver – increases bit error rate (BER)
— Transmitter –increases jitter on data stream (transmitter must have jitter below a specified level)
q VCO noise is characterized in the time domain as jitter (integral of phasenoise over the channel bandwidth)
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Prof. C. Patrick Yue Slide 5
Types of VCO
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Prof. C. Patrick Yue Slide 6
Barkhausen’s Criteria for Oscillation
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Ring Oscillators
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LC Oscillators
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Ring Oscillators vs. LC Oscillators
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LC Oscillator Properties Near Resonance
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Amplitude Feedback Loop
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Leveraging Amplifier Compression Properties as Feedback
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One-Port Model of LC Oscillators
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LC-Tank Model
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Prof. C. Patrick Yue Slide 15
Feedback-Based LC Oscillators
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Prof. C. Patrick Yue Slide 16
Capacitor or Inductor Transformer in Feedback Oscillators
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Prof. C. Patrick Yue Slide 17
Colpitts Oscillator
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Prof. C. Patrick Yue Slide 18
Analysis of Colpitts Oscillator
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Prof. C. Patrick Yue Slide 19
Simplified Circuit Model for Colpitts Oscillator
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Prof. C. Patrick Yue Slide 20
Design of Colpitts Oscillator
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Prof. C. Patrick Yue Slide 21
Colpitts Oscillator Output Swing Estimation
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Prof. C. Patrick Yue Slide 22
Hartley Oscillator
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Prof. C. Patrick Yue Slide 23
Simplified Circuit Model for Hartley Oscillator
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Prof. C. Patrick Yue Slide 24
Cross-Coupled Pair for Negative Resistance
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Prof. C. Patrick Yue Slide 25
Negative Resistance LC Oscillator
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Prof. C. Patrick Yue Slide 26
Equivalent Circuit for LC Oscillator
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Prof. C. Patrick Yue Slide 27
Equivalent Half Circuit for LC Oscillator
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Prof. C. Patrick Yue Slide 28
Design of Negative Resistance LC Oscillator
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Prof. C. Patrick Yue Slide 29
Calculation of LO Output Swing
q LO signal power at the fundamental frequency depends on the current
switching waveform
— Higher order harmonics take away some of the power available
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Prof. C. Patrick Yue Slide 30
LO Swing Calculation Using Idealized Model
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Prof. C. Patrick Yue Slide 31
Odd Harmonics of LO Output
q The odd harmonics (3rd order in particular) of the VCO are not of much concernbecause such harmonics are not detrimental to multiplication action of the mixer.
q In fact, presence of odd harmonics often helps to shape the output wave to have
sharper transitions when crossing zero, which is desirable in wireline systems.
q Note that odd harmonics do not affect the duty cycle of the resultant
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Prof. C. Patrick Yue Slide 32
Even Harmonics of LO Output
q Even harmonics of the fundamental LO frequency causes non-50% duty
cycle waveform which in turn leads to dc offset
q This is one of the reasons that differential VCOs are used
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Prof. C. Patrick Yue Slide 33
Typical Configurations of LC Oscillator
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Prof. C. Patrick Yue Slide 34
Integrated LC Components
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Prof. C. Patrick Yue Slide 35
Differential Inductor (1-to-1 Transformer) for VCO
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Prof. C. Patrick Yue Slide 36
Tuning in Oscillator
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Prof. C. Patrick Yue Slide 37
PN Junction in Reversed Bias as Varactor
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Prof. C. Patrick Yue Slide 38
MOS Varactor
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Prof. C. Patrick Yue Slide 39
Varactor Characteristics
q Q of MOS vs. PN-junction varactor is highly process and layout
dependentq Accumulation-mode MOS varactor requires additional modeling since it
is not standard IC component
q In general, MOS varactors tend to have better temperature coefficient
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Prof. C. Patrick Yue Slide 40
Practical VCO Tuning Schemes
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Prof. C. Patrick Yue Slide 41
Combining Switching Fixed Capacitors and Varactors
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Prof. C. Patrick Yue Slide 42
VCO Behavior Model
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Prof. C. Patrick Yue Slide 43
VCO Behavior Model
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Prof. C. Patrick Yue Slide 44
VCO Behavior Model
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Prof. C. Patrick Yue Slide 45
Focus on the Phase Deviation at Oscillator Output
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Prof. C. Patrick Yue Slide 46
Simplified Relationship between Output Voltage and Phase
O O S
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Prof. C. Patrick Yue Slide 47
Oscillator Output Power Spectral Density
D fi iti f Ph N i (dB /H )
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Prof. C. Patrick Yue Slide 48
Definition of Phase Noise (dBc/Hz)
O t t P S t ith S i N i
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Prof. C. Patrick Yue Slide 49
Output Power Spectrum with Spurious Noise
M t f S i N i i dB
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Prof. C. Patrick Yue Slide 50
Measurement of Spurious Noise in dBc
I t i i Ph N i i O ill t
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Prof. C. Patrick Yue Slide 51
Intrinsic Phase Noise in Oscillators
E i l t M d l f N i A l i
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Prof. C. Patrick Yue Slide 52
Equivalent Model for Noise Analysis
I d f th LC T k N R
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Prof. C. Patrick Yue Slide 53
Impedance of the LC-Tank Near Resonance
LC T k I d i T f Q
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Prof. C. Patrick Yue Slide 54
LC-Tank Impedance in Terms of Q
O erall Noise O tp t Spectral Densit
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Prof. C. Patrick Yue Slide 55
Overall Noise Output Spectral Density
Total Noise vs Intrinsic Noise
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Prof. C. Patrick Yue Slide 56
Total Noise vs. Intrinsic Noise
Output Noise Spectral Density Function
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Prof. C. Patrick Yue Slide 57
Output Noise Spectral Density Function
Separation in Amplitude and Phase Noise
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Prof. C. Patrick Yue Slide 58
Separation in Amplitude and Phase Noise
Leeson’s General Formula for Phase Noise
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Prof. C. Patrick Yue Slide 59
Leeson’s General Formula for Phase Noise
Example: Active Component Noise Same as Tank Noise
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Prof. C. Patrick Yue Slide 60
Example: Active Component Noise Same as Tank Noise
Noise Sources in Practical Oscillators
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Prof. C. Patrick Yue Slide 61
Noise Sources in Practical Oscillators
Practical Phase Noise Profile
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Prof. C. Patrick Yue Slide 62
Practical Phase Noise Profile
Leeson’s Phase Noise Model Constant F(∆f)
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Prof. C. Patrick Yue Slide 63
Leeson s Phase Noise Model – Constant F(∆f)
Phase Noise of Negative Resistance LC Oscillators
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Prof. C. Patrick Yue Slide 64
Phase Noise of Negative Resistance LC Oscillators
More Realistic F(∆f) for Negative Resistance LC Oscillators
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Prof. C. Patrick Yue Slide 65
More Realistic F(∆f) for Negative Resistance LC Oscillators
Minimizing Phase Noise
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Prof. C. Patrick Yue Slide 66
Minimizing Phase Noise
Suppressing Noise Contribution Due to Current Source
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Prof. C. Patrick Yue Slide 67
Suppressing Noise Contribution Due to Current Source
Effect of Bypass Capacitor at Tail Node
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Prof. C. Patrick Yue Slide 68
Effect of Bypass Capacitor at Tail Node
(A. Hajimir i et al. JSSC, May 1999.)
Suppressing Noise Contribution Due to Current Source
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Prof. C. Patrick Yue Slide 69
Suppressing Noise Contribution Due to Current Source
Minimize Noise Contribution Due to Cross-Coupled Devices
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Prof. C. Patrick Yue Slide 70
Minimize Noise Contribution Due to Cross Coupled Devices
Minimize Noise Contribution Due to Cross-Coupled Devices
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Prof. C. Patrick Yue Slide 71
Minimize Noise Contribution Due to Cross Coupled Devices
Current-Limited vs. Voltage-Limited Regimes
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Prof. C. Patrick Yue Slide 72
Current Limited vs. Voltage Limited Regimes
Current vs. Voltage Limited Operation in LC VCO
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Prof. C. Patrick Yue Slide 73
Current vs. Voltage Limited Operation in LC VCO
(A. Hajimir i et al. JSSC, May 1999.)
Signal Waveform in Current and Voltage Limited Regimes
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Prof. C. Patrick Yue Slide 74
Signal Waveform in Current and Voltage Limited Regimes
(A. Hajimir i et al. JSSC, May 1999.)
Supply Noise Rejection for VCO
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Prof. C. Patrick Yue Slide 75
Supply Noise Rejection for VCO
References
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References
1. Prof. M. Perrott, MIT
http://ocw.mit.edu/OcwWeb/Electrical-Engineering-and-Computer-
Science/6-776Spring-2005/CourseHome/index.htm
