Low Latency Demodulation for Atomic Force Microscopes, Part II: Efficient Calculation of Magnitude and Phase

Abstract

AbstractThis paper describes methods for doing high-speed, low latency, coherent demodulation of signals for dynamic or AC mode in Atomic Force Microscopes (AFMs), Abramovitch (2010). These demodulation methods allow the system to extract signal information in as little as one cycle of the fundamental oscillation frequency. By having so little latency, the demodulator minimizes the time delay in the servo loop for an AC mode AFM. This in turn minimizes the negative phase effects of the demodulation allowing for higher speed scanning. Part I, Abramovitch (2011), of the paper describes the mixing and integration portion of the demodulator. This part describes efficient methods for extracting magnitude and phase. In particular, the CORDIC method compared to optimized table lookup operations and a phase-locked loop (PLL) based method. The latter two show a significant decrease in latency, with the PLL based method generating the magnitude and phase with virtually no extra latency and a significant savings in resources.