Single-cycle-PLL detection for real-time FM-AFM applications

Area of Science:

• Atomic Force Microscopy
• Signal Processing
• Electronics Engineering

Background:

• Atomic Force Microscopy (AFM) is a high-resolution surface imaging technique.
• Frequency-Modulated (FM) AFM enhances sensitivity but faces demodulation bandwidth limitations.
• Phase-Locked Loops (PLLs) offer excellent noise performance for demodulation.

Purpose of the Study:

• To develop a novel PLL architecture for high-speed FM-AFM signal demodulation.
• To overcome the bandwidth limitations inherent in traditional PLL-based FM demodulators.
• To improve the noise performance and operational range of FM-AFM systems.

Main Methods:

• Implemented single-sideband (SSB) frequency upconversion to translate AFM signals to a fixed intermediate frequency (IF).
• Developed a model for AM-to-FM noise conversion in PLLs with phase-frequency detectors.
• Validated the architecture through electrical and AFM measurements using a PCB prototype.

Main Results:

• The SSB upconversion successfully translated the AFM signal to a 10 MHz IF, avoiding bandwidth limitations.
• The developed noise model predicts an upper corner frequency for demodulation bandwidth.
• The prototype demonstrated the feasibility and effectiveness of the proposed architecture.

Conclusions:

• The novel PLL architecture enables high-speed FM-AFM demodulation with improved performance.
• The SSB upconversion technique effectively addresses bandwidth limitations and broadens the usable cantilever frequency range.
• The system's noise performance is well-characterized, allowing for optimized operation.