Detecting Signals With Direct Fast Fourier Transform for Microarray Data Collection

Small signals are routinely detected at a frequency away from the 1/f noise. Typically, the signal source is modulated at a suitable frequency, and the harmonics of the modulation frequency in the signal are analyzed with phase sensitive detectors such as Lock-in amplifiers. Yet, the high cost and poor portability of stand-alone Lock-in amplifiers are obstacles to making such an approach of harmonic detection into a widely usable instrumentation. In this letter, we show that for many applications where signals are not too small (e.g., more than tens of micro-volts) the direct fast Fourier transform using a commercially available, general-purpose data acquisition board serves as a cost-effective alternative to Lock-in amplifiers without sacrificing the signal-to-noise ratio.