Monolithic PhaseLocked Loops for Wideband CDMA Applications

1
Monolithic Phase-LockedLoops for Wideband CDMA
Applications

• Chinh Doan
• Robert W. Brodersen
• University of California, Berkeley
• BWRC Retreat
• June 1999

2
Frequency Synthesizer Requirements
cos 2pfRFt
PN Code
RF input (fRF)
A/D
I (800 kS/s)
A/D
Q (800 kS/s)
BB Filter
Correlator
sin 2pfRFt

• Fixed frequency for direct downconversion
• Processing gain reduces effect of reciprocal
  mixing
• Correlation decreases RMS phase noise

Relaxed requirements Low power, fully
integrated, CMOS implementation
3
Modeling PLL Phase Noise (Simulink)
4
Effect of Correlation on RMS Phase Noise

• Correlating filters out high frequency (fm gt
  fsymbol) phase noise
• Use wide bandwidth PLL to take advantage of
  correlation

5
Phase-Locked Loop Fundamentals
Phase Detector
Loop Filter
VCO
fref
fout
fdiv
N

• Phase Detector DC value of output µ fref - fdiv
• Loop Filter sets noise and transient performance
  of PLL
• VCO output frequency controlled by input voltage
• Frequency Divider fdiv fout/N

6
Phase Detector and Loop Filter
Up
ZF(s)
Ref
Vctrl
Reset
D
Dn
Q
Div
CK
Phase/Frequency Detector
Charge Pump
Active Loop Filter

• Phase detector implemented using DCVSL to reduce
  static power and leakage current in charge pump
• Current mismatch in charge pump is major cause of
  spurious tones
• Fully differential, active loop filterrequired
  to minimize spurs

7
Voltage-Controlled Oscillator
Ring Oscillator

• Large tuning range to compensate for process
  variations
• Poor phase noise shaped by wide bandwidth PLL
• I/Q outputs
• Source-coupled logic levels compatible with
  Gilbert mixer

8
Frequency Dividers (HSPICE Simulations)
D
Q
D
Q
CK
CK

• Fabricated in 0.25 mm CMOS process
• Operates up to 3.7 GHz
• Consumes 1.1 mW

9
Current Status and Future Work

• Current Status
• Fabricated low-power, high-speed frequency
  dividers
• Simulink models of PLL to determine system level
  impairments and specifications
• Designed and simulated VCO and PFD
• Future Work
• Measure performance of frequency dividers
• Circuit design of charge pump and loop filter
• Fabrication of complete frequency synthesizer
• Tape out in Summer 1999