Multiplexed multiple-{τ} auto- and cross- correlators on a single FPGA

Fluorescence correlation and cross-correlation spectroscopy (FCS, FCCS) are widely used techniques to study the diffusion properties and interactions of fluorescent molecules. Autocorrelation (ACFs) and cross-correlation functions (CCFs) are typically acquired with fast hardware correlators. Here we introduce a new multiple-{\tau} hardware correlator design for computing ACFs and CCFs in real time. A scheduling algorithm minimizes the use of hardware resources by calculating the different segments of the correlation function on a single correlator block. The program was written in LabVIEW, enabling computation of two multiple-{\tau} ACFs and two CCFs on a National Instruments FPGA card (NI 7833R) in real time with a minimal sampling time of 400 ns. Raw data are also stored with a time resolution of 50 ns for later analysis. The design can be adapted to other FPGA cards with only minor changes and extended to evaluate more inputs and correlation functions.