High-resolution multiple channel frequency counter using spartan-3E FPGA

Abstract

Frequency counter resolution, accuracy and precision are importance parameters of the quartz crystal microbalance signal acquisition. The sensitivity of the quartz crystal microbalance is not only depended on the resonance frequency of the sensor but also the resolution of the counter. Higher counter resolution results in higher sensitivity measurement of the sensor output. In this work, a three-channel reciprocal frequency counter was developed using FPGA and implemented using VHDL code. The precision and resolution of the system depend on the system clock source. In this development, a high-precision TCXO oscillator with a resonance frequency of 100MHz is used as a reference oscillator. From this oscillator, one-second time gate and period measurement is constructed in the FPGA. In each measurement channel, dual digital counters were implemented. One counter counts the incoming signal in between one-second gate, and the other counter is counting the 100MHz signal from the beginning to the end of the counted signal within the one-second gate. The accuracy of the frequency measurement of the counter was calibrated using 10MHz standard rubidium oscillator. The developed system shows a good performance and able to count incoming signal with an accuracy of 0.1 Hz for one second acquisition time.