A Low Phase Noise VCO Design For PCS Handset Applications

Introduction

The VCO design in a PCS handset must satisfy a number of stringent electrical, cost, and size requirements which include:

• Power supply
  • 3 V DC power supply
  • < 6 mA total current consumption
• Layout
  • Minimum components count
  • Aggressive PCB layout design and component placement rules with spacing less than 5 mils and placement pads no larger than component's land area
  • Total VCO footprint smaller than 7 x 8 mm
• Cost
  • Minimum component cost
  • Maximum production yield
  • Tight component tolerance control to minimize or avoid trimming
  • Total VCO cost well under $0.50

The factors that have significant impact on the primary VCO electrical specifications may be summarized as follows:

• Primary design criteria
  • Frequency tuning range
  • Tuning sensitivity
  • Output power level
• Stability and spectrum purity factors
  • Phase noise at a given frequency offset
  • Frequency pulling when terminated with SWR > 2 at all phases
  • Frequency pushing
  • Temperature stability

Other electrical specifications may include harmonic content or spur levels in the output signal, tuning linearity, etc. However, for the existing handset VCO market these specifications have been standardized based on available technology.

This article describes the design and performance of a VCO centered at 1750 MHz for a PCS handset that uses the SMV1763-079 varactor diode. This low R varactor was designed specifically for low phase noise applications. The VCO was designed to satisfy the listed requirements for a PCS handset.

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•Application Note: A Low Phase Noise VCO Design For PCS Handset Applications