Fine Frequency Control Using The SKY72300, SKY72301, and SKY72302 Dual Synthesizers/PLLs

Many techniques currently exist for synthesizer frequency output control. These techniques, from simple to complex, manipulate the crystal oscillator to maintain a specific output frequency. All of these techniques have associated cost and parts count considerations.

This Application Note describes the fine frequency control of Skyworks SKY72300, SKY72301, and SKY72302 fractional-N synthesizers using a Voltage Controlled Oscillator (VCO). This method is a simple and low-cost alternative to pulling the crystal reference frequency to manipulate the final output frequency.

The technique has the following applications:

• Radio calibration
• Automatic Frequency Control (AFC)
• Reference crystal accuracy
• Reference crystal temperature compensation
• Reference crystal aging compensation
• Doppler correction