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In The Name Of God. Design And Implementation Of Frequency Synthesizer And Interrogating Phase Noise In It's Parts. Advisor Professor : Dr.Sadr & Dr.Tayarani Students: Majid Sodagar Mehran Mohammadi Izad. Brief Review. Introduction Block Diagrams Models Oscillator Divider - PowerPoint PPT Presentation
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Design And Implementation Of Frequency Synthesizer And Interrogating Phase NoiseIn It's Parts
Advisor Professor : Dr.Sadr & Dr.TayaraniStudents:
Majid SodagarMehran Mohammadi Izad
In The Name Of God
Brief Review
• Introduction• Block Diagrams• Models
– Oscillator– Divider– Charge Pump
• Design And Measurements• Conclusions
Signals Suffer From Noise !
Introduction & Motivation
• The GSM system needs very narrow channel spacing
• Thus low phase noise levels are required.
• e.g. , At 1 kHz from the carrier, a single sided spectral noise density of -80 dBc/Hz
Conventional Synthesizer Block Diagram
PLL Block Diagram And Noise Sources
Transfer Functions
1 1( )
( ) !1 1
1 ( )
v
Refv
K K z sPNout R SH s LowPassPN K K z s
S N
1( )
( ) !1 1
1 ( )
v
CPv
K z sPNout SH s LowPassPN K K z s
S N
1( ) !
1 11 ( )vco
v
PNoutH s HighPass
PN K K z sS N
1
1( )
( ) !1 1
1 ( )
v
divider vN
K K z sPNout SH s LowPassPN K K z s
S N
Typical Superposition Of All Sources
Oscillator Noise Modeling
• LTI Model (Leeson-Cutler)- Ignoring Time Variance Nature of
Oscillator
• LTV Model (Hajimiri-Lee)- Take the Time Variance Nature of
Oscillator into account.
Typical LC Oscillator
A = Excess noise FactorN = For Active Inductor
LTI Model
Using Only Z(s) of tank circuit
Typical Phase Noise Slopes Close to Career
LTV Model
• Every oscillator is a quasi periodic system
• the noise analysis should take this into account
• Model Benefits:– Design Aspects– Cyclostationary noise
Impulse Response
The constant qmax = CVpeak issimply a normalization constant, thepeak charge in the oscillator.
Graphical Interpretation
Divider Block Model
Divider Noise Model
2
,
2( ) ( ) ( )
vco
vcof w lf
f MS f S f S f
n
Filter Noise
• Ignoring Thermal noise of Passive elements And Current Noise
Typical OpAmp Input Voltage Noise
• Our OpAmp Performance (OP27): 3nv
RMS Voltage noiseHz
2ncf Hz
Charge Pump PFD Structure
• Lead And Lag Detection• Increasing Lock Range• Reduction of cycle slipping
Effects Of CP PFD On Phase Noise
• Effect of Leakage On reference Spurs– Charge pump is off majority of the
Time– Leakage causes VCO tuning voltage
to change• Effect of Mismatch On reference Spurs
– The width of correction pulses is related to the mismatch
– causes the AC voltages• undesirable AC voltages Causes FM
modulation
Experimental Results for FM modulation (Spurs)
Reference Spur example
CP Phase noise model
• Where
– Fc = Flicker Corner Frequency– Fm = Offset From Carrier– I0 = current noise Floor
0( ) 10log 1 cm
m
fL f I
f
2 /A Hz
2 RefK
Stability problem In CP PLL
• The charge pump nature is discrete so it is prone to instability
• The following condition should be satisfied to use continuous time analysis !!
Our Design
Design Specification
• Design for GSM requirements
– Fref = 10MHz– Fcomp = 200KHz– LoopBandWidth = 15KHz– RFOut = 800 – 1100 MHz– PhaseMargin = 45 deg
Schematic
Active Filter
Simulated Open Loop Response
Passive Phase Noise Result @1KHz
Phase noise = -53.7-10log(200) = -76.7 dBc/Hz
Passive Phase Noise Result @10KHz
Phase noise = -51.9-10log(200) = -74.9 dBc/Hz
Passive Phase Noise Result @100KHz
Phase noise = -70.2-10log(500) = -92.9 dBc/Hz
Step Response And Lock Time
• Settling time = 150 sec
Active Phase Noise Result @1KHz
Phase noise =-55.1-10log(200)= -78.1 dBc/Hz
Active Phase Noise Result @10KHz
Phase noise =-49.7-10log(200)=-72.7 dBc/Hz
Inappropriate Opamp Bias !!!
Causing excess noise near the career
1Hz Normalize Phase Noise
• Good way for characterize the phase noise of PLL
• Assumes charge pump phase noise is dominant
• PN=PN1Hz+20logN+10log(Fcomp)
Experimental Result:
• For our design:
– PN1Hz = -205 dBc/Hz– N = 4500– Fcomp = 200KHz– PN =-205+20log(4500) +10log(200KHz)
= -78.9 dBc/Hz
Conclusions
• By using better synthesizer, its possible to achieve lower Phase noise
• If the CP noise Dominates in the circuit, then we can not detect the effect of Active filter noise
• Any Question?
Thanks